HK1172315B - Suspended media membrane biological reactor system and process including multiple biological reactor zones - Google Patents

Description

Suspended media membrane bioreactor system and method comprising a plurality of bioreactor sections

RELATED APPLICATIONS

The present application claims the benefit of U.S. provisional patent application No. 61/224,000, filed on 7/8/2009 and U.S. provisional patent application No. 61/186,983, filed on 6/15/2009, the entire contents of which are incorporated herein by reference.

Technical Field

The present application relates to wastewater treatment systems and methods.

Background

The effective treatment of domestic and industrial wastewater is an extremely important aspect of improving quality of life and maintaining clean water. Up to about half a century ago, the problems of simply discharging wastewater to water sources such as rivers, lakes, and oceans were evident, and biological and chemical wastes endangered all life forms, including the spread of infectious diseases and exposure to carcinogenic chemicals. Thus, wastewater treatment programs have emerged from ubiquitous municipal wastewater treatment facilities to clean sanitary wastewater from populations, through specialized industrial wastewater treatment processes to treat specific pollutants from a variety of industrial applications.

Biologically refractory and biologically inhibitory organic and inorganic compounds are present in certain industrial and sanitary wastewater streams to be treated. Various attempts have been made to address the treatment of these biologically intractable and biologically inhibitory compounds. Certain types of known treatments include the use of powdered activated carbon to adsorb and subsequently remove biologically refractory and biologically inhibitory organic compounds.

Nevertheless, there remains a need to treat wastewater containing biologically intractable and biostatic organic and inorganic compounds without the use of powdered activated carbon and other drawbacks associated with the prior art.

Summary of The Invention

In accordance with one or more embodiments, the present invention is directed to a system and method for treating wastewater.

In accordance with one or more embodiments, the present invention is directed to a wastewater treatment system for treating wastewater. The system comprises a first biological reaction section, a second biological reaction section and a membrane operation system. The first biological reaction zone is constructed and arranged to receive and treat the wastewater. The second biological reaction zone includes a separation subsystem and is constructed and arranged to receive effluent from the first biological reaction zone. A suspension system for adsorbent material is disposed in the second biological reaction zone. The membrane operating system is located downstream of the second biological reaction zone and is constructed and arranged to receive treated wastewater from the second biological reaction zone and to discharge membrane permeate.

According to one or more embodiments, the first and second biological reaction zones are separate portions of the same vessel.

According to one or more embodiments, the first biological segment and the second biological segment are located in separate vessels.

According to one or more embodiments, the suspension system comprises an air-lift suspension system. The gas lift suspension system may include at least one draft tube positioned within the second biological reaction zone and a gas conduit having one or more apertures positioned and dimensioned to direct gas to an inlet end of the draft tube. Alternatively, the gas lift suspension system may comprise at least one draft tube located within the second biological reaction zone and a gas conduit having one or more apertures positioned and dimensioned to direct gas to the bottom of the draft tube.

According to one or more embodiments, the suspension system comprises a jet suspension system.

According to one or more embodiments, the separation subsystem comprises a mesh screen located at the outlet of said second biological reaction zone.

According to one or more embodiments, the separation subsystem includes a deposition section located proximal to the outlet of the bioreactor. The deposition section may include first and second baffles positioned and sized to define a stationary section, wherein the adsorbent material is separated from the mixed liquor and deposited within the mixed liquor at the bottom of the bioreactor. Additionally, the deposition section may comprise a mesh screen or weir located proximal to the outlet of the second biological reaction section.

In accordance with one or more embodiments, the present invention relates to a wastewater treatment system wherein an adsorbent material source introduction device is in communication with the second biological reaction zone. Further, the sensor is constructed and arranged to determine a system parameter. Additionally, a controller is in electronic communication with the sensor and is programmed to direct performance of an action based on the measured system parameter. The measured parameter may be the concentration of one or more predetermined compounds. The action can include removing at least a portion of the adsorbent material from the second biological reaction zone, and/or adding adsorbent material to the second biological reaction zone.

In accordance with one or more embodiments, the present invention is directed to a wastewater treatment system for treating wastewater. The system includes a first biological reaction zone having a wastewater inlet and a first zone mixed liquor outlet. The system also includes a second biological reaction zone having: a mixed liquor inlet in fluid communication with the first zone mixed liquor outlet, a suspension system for adsorbent material, a second zone mixed liquor outlet, and a separation subsystem associated with the second zone mixed liquor outlet. The system further includes a membrane operating system downstream of said second biological reaction zone having: an inlet in fluid communication with said second zone mixed liquor outlet, and a treated effluent outlet.

In accordance with one or more embodiments, the present invention is directed to a wastewater treatment process. The method comprises the following steps: introducing the mixed liquor into a first biological reaction zone to form a treated mixed liquor; sending said treated mixed liquor to a second biological reaction zone; suspending adsorbent material in said treated mixed liquor of said second biological reaction zone, the suspending action being operated under conditions promoting adsorption of contaminants in the treated mixed liquor onto said adsorbent material; and passing an effluent substantially free of adsorbent material from the second biological reaction zone to a membrane operating system while maintaining adsorbent material in the second biological reaction zone.

Details of even other aspects, implementations, and advantages of these exemplary aspects and implementations are discussed below. Moreover, it is to be understood that both the foregoing general description and the following detailed description are merely exemplary of various aspects and embodiments, and are intended to provide an overview or framework for understanding the nature and character of the aspects and embodiments as they are claimed. The accompanying drawings are included to provide an illustration and a further understanding of the various aspects and embodiments, and are incorporated in and constitute a part of this specification. The drawings, together with the remainder of the specification, serve to explain the principles and operations of the aspects and implementations described and claimed herein.

Brief Description of Drawings

The present invention will be described with additional specificity and detail through the use of accompanying drawings in which apparatus, systems and methods are described and/or illustrated. In the drawings, which are not necessarily to scale, like elements are illustrated by like reference numerals throughout the several views. In the drawings:

FIG. 1 is a schematic view of a membrane bioreactor system using bioreactors containing one or more sections with suspended adsorbent material;

FIG. 2 is a schematic of an embodiment of a system for treating wastewater using a bioreactor of adsorbent material upstream of a membrane operating system;

FIG. 3 is a schematic view of a second embodiment of a system similar to that shown in FIG. 2 but including a denitrification section;

FIG. 4 is a schematic view of another embodiment in which the adsorbent material is maintained in suspension only in a portion of the bioreactor tank;

FIG. 5 is a schematic diagram of yet another embodiment of a bioreactor divided into a plurality of sections, including anoxic sections;

FIG. 6 is a schematic diagram of another embodiment using an array of bioreactors (in which the adsorbent material is maintained in suspension in only one of the bioreactors);

FIGS. 7 and 8 are embodiments of a bioreactor system showing a jet suspension system for suspending adsorbent material in a mixed liquor;

FIGS. 9 and 10 are alternative embodiments of a bioreactor system showing a jet suspension system for suspending adsorbent material in a mixed liquor from a source from which the adsorbent material has been removed;

FIG. 11 is an alternative embodiment showing a spray suspension system for suspending adsorbent material in a mixed liquor wherein the adsorbent material is not circulated through the spray nozzle;

FIG. 12 is a further embodiment of a bioreactor showing a gas lift suspension system to provide circulation to maintain adsorbent material in suspension;

FIGS. 13A and 13B are further embodiments showing a deposition zone;

FIG. 14 is a graph showing feed COD concentration (in mg/L), and remaining effluent COD concentration (in percent of initial value) at various stages of biological acclimation in a membrane bioreactor system;

FIG. 15 is a schematic explanatory view of an embodiment of a spray nozzle of the type used in an example of use of the spray levitation system;

FIG. 16 is a schematic illustration of a system configuration used in another example herein;

FIG. 17 is a graph showing the adsorbent material suspension velocity and liquid flow rate under certain nozzle throats measured under various test conditions using the system configuration of FIG. 16;

FIGS. 18 and 19 show top and cross-sectional views of an embodiment of a bioreactor employed in the system configuration of FIG. 16;

FIG. 20 is a graph showing abrasion loss as a function of run time for various types of adsorbent materials in another example of an airlift suspension system used herein;

FIG. 21 shows a top view and a cross-sectional view of an embodiment of a bioreactor using an air-lift suspension system;

FIG. 22 is a schematic illustration of the flow pattern using the air-lift levitation system of FIG. 21;

FIG. 23 shows a top view and a cross-sectional view of a bioreactor embodiment using another configuration of an air-lift suspension system; and

FIGS. 24 and 25 show top, side, and end sectional views of bioreactor embodiments using various configurations of air lift suspension systems.

Detailed Description

As used herein, "biologically refractory compounds" refer to the classes of chemical oxygen demand ("COD") compounds (organic and/or inorganic) in wastewater that are difficult to biodegrade when contacted by microorganisms. "biologically intractable compounds" can have a variety of intractable levels ranging from mild to highly intractable.

"biostatic compounds" refer to those compounds (organic and/or inorganic) in wastewater that inhibit the biological decomposition process.

"Biolability" refers to simple organic matter such as human and animal excreta, food waste, and inorganic matter such as ammonia and phosphorus-based compounds that are readily digestible.

"COD" or "chemical oxygen demand" refers to a measure of the ability of water to consume oxygen during chemical reactions leading to the oxidation (decomposition) of organic matter and the oxidation of inorganic chemicals such as ammonia and nitrite. COD measurements include biologically unstable, biologically inhibitory and biologically refractory compounds.

"mixed liquor suspended solids" or "MLSS" refers to dissolved and suspended microorganisms and other substances present in the wastewater being treated; "mixed liquor volatile suspended solids" or "MLVSS" refers to the active microorganisms in MLSS; and "mixed liquor" means a combined mixture of wastewater and MLSS.

As used herein, "adsorbent" or "adsorbent material" means that the granular activated carbon includes materials that have been treated to provide an affinity for a predetermined chemical species, metal, or other compound present in the wastewater to be treated; a compound based on granular iron such as an iron oxide complex; a synthetic resin; and a particulate aluminum silicate compound.

In the context of the presence of adsorbent material described in the effluent from one section of the system to another, e.g., from a bioreactor containing suspended adsorbent material to a membrane operating system, the term "substantially free of or" substantially free of "refers to an amount that limits the amount of adsorbent material sent to the membrane operating system from an amount that does not adversely affect the efficiency required by the membrane filtration procedure therein. For example, in certain embodiments, "substantially free of" or "substantially free of" refers to a predetermined amount of adsorbent material used within a given system within a bioreactor or one or more biological reaction zones, up to at least about 80 volume percent; in additional embodiments at least about 90 vol%, and in still other embodiments at least about 95 vol%, and in still other embodiments at least about 99 vol%. It will be appreciated by those skilled in the art based on the teachings herein that these percentages are for illustration purposes only and may vary depending on factors including, but not limited to, the type of membrane used and its corrosion resistance, the desired effluent quality, the predetermined amount of adsorbent material used in a given system, and other factors.

The invention relates to a wastewater treatment system and a method. As used herein, "wastewater" defines any water to be treated that flows into a wastewater treatment system, such as surface water, ground water, and wastewater streams from industrial, agricultural, and municipal sources, having biodegradable material contaminants, inorganic substances that can be decomposed by bacteria, labile organic compounds, biologically intractable compounds, and/or biostatic compounds.

Wastewater from industrial and municipal sources typically contains biosolids, as well as inerts and organics, including biostatic and biologically refractory organics. Examples of biostatic and biocompatable organic compounds include synthetic organic chemicals, such as polyelectrolyte treatment chemicals. Other biologically inhibitory and intractable organic materials include polychlorinated biphenyls, polycyclic aromatic hydrocarbons, polychlorinated dibenzo-p-dioxins, and polychlorinated dibenzofurans. Endocrine disrupting compounds also belong to a class of biostatic and biologically intractable organisms that may affect the hormonal system of the organism and are present in the environment. Endocrine disrupting compounds include: alkylphenol compounds, such as nonylphenol for removing fats and oils, and natural hormones and synthetic steroids found in contraceptives, such as 17-b-estradiol, estrone, testosterone, ethinyl estradiol.

Other examples of wastewater to be treated include: high-strength wastewater; low-strength wastewater; and leachate from the landfill. The water may also be treated to remove viruses. Other examples of contaminants in wastewater include: flame retardants, solvents, stabilizers, polychlorinated biphenyls (PCBs); dioxins; furans; polynuclear aromatic compounds (PNA); drugs, petroleum; a petrochemical product; petrochemical by-products; cellulose; phosphorus; phosphorus compounds and derivatives; and agricultural chemicals such as those derived from or used in the manufacture of fertilizers, pesticides, and herbicides.

Wastewater from industrial and municipal sources also contains trace amounts of constituent compounds that originate from the water treatment process and are subsequently difficult to remove. Examples of minor ingredients introduced during water treatment include nitrosamines, such as N-Nitrosodimethylamine (NDMA), which may be released from proprietary cationic and anionic resins.

Generally, wastewater treatment facilities use multiple treatment stages to clean water so that it can be safely released into bodies of water such as lakes, rivers, and streams. Currently, many sanitary sewage treatment plants include a preliminary treatment stage in which mechanical devices are used to remove large objects (e.g., bar screens) and sand or gravel channels are used to deposit sand, gravel and stones. Some treatment systems also include a first stage where some fats, greases and oils float to the surface for skimming and heavier solids settle to the bottom and are then treated in either an aerobic or anaerobic digestion tank to digest biomass and reduce the biosolids content.

After the primary treatment and/or primary treatment, the wastewater is sent to a secondary biological activated sludge treatment stage. Biological treatment of wastewater is widely practiced. Wastewater is often treated with waste activated sludge, in which biosolids are acted upon by bacteria in a treatment tank. The activated sludge procedure involves aerobic biological treatment in an aeration tank, typically followed by a clarifier/settling tank. The settled sludge is recycled back to the aeration tank to obtain a sufficient mixed liquor suspended solids concentration to digest the contaminants. Some alternative routes that may be used to dispose of excess biosolids, such as sludge, include, but are not limited to, incineration, disposal in landfills, or as fertilizer if free of toxic components.

In the aeration tank, oxygen-containing gas such as air or pure oxygen is added to the mixed liquor. Oxygen from the air is typically used by bacteria to biologically oxidize suspensions dissolved or carried in the wastewater feed. Biological oxidation is typically the lowest cost oxidation process that can be used to remove organic pollutants and other inorganic compounds such as ammonia and phosphorus compounds from wastewater; and is the most widely used wastewater treatment system for treating wastewater contaminated with biologically treatable organic compounds. Wastewater containing chemicals that resist biological decomposition, bio-inhibitory compounds, and/or biologically refractory compounds may not be adequately treated by conventional simple biological wastewater treatment systems. These compounds can only be acted upon by bacteria for the residence time that water remains in the treatment tank. Since water retention times are often insufficient for biological oxidation of sufficient quantities of biostatic and/or biologically refractory compounds, it is possible that some of these recalcitrant compounds are not treated or destroyed and pass through the treatment process unaltered or are only partially treated before being discharged into the effluent or excess residual sludge.

The mixed liquor effluent from the aeration tank typically enters a clarifier/settling tank where sludge, including concentrated mixed liquor suspended solids, is deposited by gravity. The excess biomass is discarded, i.e., discharged to the outside of the plant for disposal. However, some biological oxidation systems use different treatment methods to remove solids from the wastewater effluent based on wastewater and economic needs. The clarifier/settling tank may be replaced with a membrane operating system or other unit operation, such as the use of a dissolved air/induced flotation device. The liquid effluent from the clarifier/settling tank, operating system or dissolved air flotation unit is either discharged or subjected to further treatment prior to discharge. The solids removed from the mixed liquor are returned to the aeration tank as return activated sludge for further treatment and to maintain the proper bacterial concentration in the system. Some portion of this returned activated sludge is periodically removed from the recycle line to control the concentration of bacteria in the mixed liquor.

A recent development in conventional industrial biological wastewater treatment plant technology involves the addition of powdered activated carbon particles to the mixed liquor. In biological processes using powdered activated carbon, organic matter may be adsorbed onto the activated carbon and retained in the treatment tank for a water retention time, which is similar to the sludge retention time, thus performing adsorption processes and biological processes, resulting in increased removal of certain biologically inhibitory or biologically refractory compounds. In these procedures, certain organic and inorganic compounds are physically adsorbed onto the surface of the powdered activated carbon particles.

Powdered activated carbon has been used in conventional biological treatment plants because it can adsorb bio-inhibitory or bio-refractory compounds, thereby providing effluent containing lower concentrations of these contaminants. The mixed liquid contains powdered activated carbon to provide multiple operation effects. Carbon provides the advantages of suspension media biological treatment systems, including increased contaminant removal and increased resistance to turbulent conditions. In addition, carbon allows for the adsorption of bio-inhibitory or bio-refractory compounds onto the carbon surface and exposure toBiological treatment takes a significantly longer time than conventional biological treatment systems, thereby providing an effect similar to that of a fixed film system. Carbon also allows the evolution of certain bacterial products to be more digestible over biologically inhibitory organic matter. The continuous circulation of the carbon back to the aeration tank containing the returned activated sludge, i.e. the sludge retention time, means that the bacteria can act on the digestion of the biostatic organic compounds adsorbed on the carbon surface for a longer time than the water retention time of the biological treatment system. This approach also results in the biological regeneration of carbon and allows carbon to remove significantly larger amounts of bio-inhibitory or bio-intractable compounds than simple packed bed carbon filtration systems, which also require frequent carbon replacement or expensive physical regeneration of carbon once the carbon's adsorption capacity is exhausted. The carbon in the mixed liquor also adsorbs certain compounds, thereby providing a bleed stream that is free of or substantially contains a lower concentration of compounds that are not completely resistant to conventional biological oxidation treatment or to biological decomposition. One example of a known powdered activated carbon system is sold under the trademark "PACT" by Siemens Water Technologies, Inc. (Siemens Water Technologies)"supply.

However, excess solids are wasted because both biological growth and adsorption of organic and inorganic compounds occurs on the powdered form of activated carbon. In addition, the discharge of powdered activated carbon from the treatment process is accompanied by the removal of biosolids and therefore must be continuously replenished.

Increasingly, sanitary wastewater is treated using membrane bioreactor technology, which provides improved effluent quality, a smaller physical footprint (more wastewater can be treated per unit area), increased tolerance to turbulence, improved ability to treat difficult-to-treat wastewater, and a number of other operational advantages. For example, wastewater containing high total dissolved solids can encounter sedimentation problems in conventional clarifiers/settling tanks, requiring solids separation devices such as dissolved air flotation devices or other solids removal systems that are significantly more difficult to operate. Although membrane bioreactors can remove the sedimentation problems encountered with clarifier/settling tank systems, there are often membrane fouling and foaming problems that do not occur with conventional clarifier system. The fouling may be a result of extracellular polymeric compounds resulting from the breakdown of biological life forms in the mixed liquor suspended solids, the accumulation of organic matter such as oils, or the flaking through inorganic matter.

Furthermore, membrane bioreactors have not been commercially used to date for the addition of powdered activated carbon. Powdered activated carbon has been used in surface water treatment systems that utilize membranes for filtration. However, these surface water treatment systems utilizing membrane and powdered activated carbon have been reported to suffer from carbon erosion films and carbon persistent plugging and/or fouling films.

Industrial waste water that is treated prior to discharge or reuse often includes oily waste water, which may contain emulsified hydrocarbons. Oily wastewater may come from a variety of industries including the steel and aluminum industries, chemical processing industries, automotive industries, laundry industries, and crude oil manufacturing and petroleum refining industries. As discussed above, some amount of un-emulsified oil and other hydrocarbons may be removed in a single treatment procedure where floating oil is skimmed off the top. Biological secondary wastewater programs are generally employed to remove residual oil, typically dissolved and emulsified oil, from the wastewater, but some free oil may be present. Typical hydrocarbons remaining after a single treatment include lubricants, cutting fluids, tars, crude oil, diesel, gasoline, kerosene, jet fuel, and the like. These hydrocarbons are typically removed before the water is discharged to the environment or the water is reused in an industrial process. In addition to governmental regulations and ecological considerations, effective removal of residual hydrocarbons is also advantageous because properly treated wastewater can be used in a variety of industrial processes, and eliminates raw water treatment costs and reduces regulatory discharge problems.

Other types of wastewater to be treated include contaminated process water from other industrial processes such as the manufacture of pharmaceuticals, various goods, agricultural products (e.g., fertilizers, pesticides, herbicides) and paper and medical wastewater.

The commercial deployment of membrane bioreactors for the treatment of oily/industrial wastewater is slow, mainly due to maintenance issues associated with oil and chemical fouling membranes. The industrial/oily wastewater treated in the membrane bioreactor (where powdered activated carbon is added to the mixed liquor) tested indicates the same treatment advantages observed in conventional biological wastewater treatment systems including powdered activated carbon. It has also been found that the advantages of using a membrane bioreactor can also be achieved. However, the membrane bioreactors with and without the powdered activated carbon are verified in parallel, and the membrane bioreactor with the powdered activated carbon provides treatment advantages compared with the membrane bioreactor without the powdered activated carbon. Furthermore, membrane bioreactors without added powdered activated carbon are extremely difficult to operate due to dissolved organic matter and additional extracellular polymeric compounds fouling the membrane. The test further verifies that: while the addition of powdered activated carbon provides a very useful biological wastewater treatment system, carbon has the adverse effect of producing a significant amount of abrasion and irreversible fouling of the membrane. Such abrasion and irreversible fouling are significant enough to render the operation of such systems extremely expensive due to the significantly shortened life expectancy of the membranes and the frequent cleaning of the membranes.

The system and method of the present invention overcomes the adverse effects of using powdered activated carbon while providing the same and additional advantages.

Referring to fig. 1, a wastewater treatment system 100 is schematically shown to include a bioreactor system 102 upstream of a membrane operating system 104. In certain embodiments, bioreactor system 102 comprises a single bioreactor vessel. In additional embodiments, bioreactor system 102 comprises a plurality of bioreactor vessels, a bioreactor vessel divided into separate sections, or a plurality of bioreactor vessels wherein some or all are divided into separate sections. The individual reactor vessels or divided sections are generally referred to herein as bioreaction sections. During wastewater treatment operations according to the present invention, the adsorbent material along with the microorganisms are maintained in suspension throughout the biological reaction zone or a subset of the total number of biological reaction zones. The membrane operating system 104 is maintained substantially free of adsorbent material using one or more of the separation subsystems described herein. The influent wastewater stream 106 may be introduced from a primary treatment system, a primary screening system, or in direct series flow as previously untreated wastewater. In additional embodiments, the influent wastewater stream 106 may be previously treated wastewater, such as effluent from one or more upstream bioreactors, including but not limited to aerobic bioreactors, anoxic bioreactors, continuous flow reactors, sequencing batch reactors, or other types of biological treatment systems that may biologically decompose organic matter and, in certain embodiments, certain inorganic compounds.

The bioreactor and/or certain bioreactor sections may be various types of bioreactors including, but not limited to, aerobic bioreactors, anoxic bioreactors, continuous flow reactors, sequencing batch reactors, trickling filters, or other types of biological treatment systems that can biodegrade organics and, in certain embodiments, certain inorganic compounds.

Further, the bioreactor and/or certain bioreactor sections used herein may be of any size or shape suitable for suspending adsorbent materials in conjunction with a suspension system. For example, the container may have a cross-sectional area of any shape, such as circular, oval, square, rectangular, or any other irregular shape. In certain embodiments, the container may be constructed or modified to facilitate proper suspension of the adsorbent material.

FIG. 2 schematically shows a process flow diagram of a wastewater treatment system 200 for producing treated effluent having reduced concentrations of biologically unstable, biologically intractable, biologically inhibitory and/or organic and inorganic compounds that are all resistant to biological decomposition. System 200 generally includes a bioreactor 202 and a membrane operating system 204. Bioreactor 202 includes an inlet 206 for receiving wastewater and an outlet 208 for discharging biologically treated effluent, including mixed liquor volatile suspended solids and/or mixed liquor, to membrane operating system 204.

Bioreactor 202 includes a dispersed mass of porous 236 adsorbent material 234 and an effective amount of one or more microorganisms 238, both attached to the adsorbent material and free floating for acting on biologically unstable and certain biologically refractory, bio-inhibitory compounds in the mixed liquor separately from the adsorbent material in the mixed liquor. The adsorbent material adsorption sites, including the outer surfaces of the adsorbent particles or granules and the walls of the pores 236, initially serve as adsorption sites for biologically labile, biologically refractory, biologically inhibitory and/or organic and inorganic compounds that are entirely resistant to biological decomposition. In addition, microorganisms 238 may be adsorbed to the adsorption sites of the adsorbent material. This allows for a preferred degree of digestion of certain biologically refractory and/or biostatic compounds without proportionately longer water residence times and sludge residence times, since in practice some biologically refractory and/or biostatic compounds remain on the adsorbent material that is sequestered or retained in the bioreactor for a long time.

Often the biological instability and certain inorganic substances will be digested relatively rapidly, mainly by microorganisms that are not adsorbed to the adsorbent material, i.e., free-floating microorganisms in the mixed liquor. Some components, including organic and inorganic substances that are entirely resistant to biological decomposition and biologically refractory and biologically inhibitory compounds that are extremely recalcitrant, will remain adsorbed on the adsorbent material or may be adsorbed and/or absorbed by the free-floating biological material in the reactor. Finally, these indigestible compounds will concentrate on the adsorbent until the adsorbent needs to be replaced to maintain the effluent at an acceptable level of adsorption capacity. When the adsorbent material is left in the system according to the invention, microorganisms grow and are retained on the adsorbent material, typically for a time sufficient to break down at least some of the biologically refractory and/or biostatic compounds in the particular influent wastewater that has concentrated on the adsorbent material. Furthermore, while not wishing to be bound by theory, it is believed that the microorganisms eventually evolve into mature products with the special acclimation required to break down the intractable compounds in the particular influent wastewater. Over additional time, such as days to weeks, as the system becomes acclimated, wherein the adsorbent material containing certain biologically refractory and/or biostatic compounds remains in the system, the highly specific microorganisms become second, third and higher generations, thereby increasing their effectiveness in biodegrading the particular biologically refractory and/or biostatic compounds present in the particular influent wastewater. This is illustrated by the stepwise change in residual COD shown in figure 14, which shows a plot of feed concentration (expressed as milligrams per liter) and residual effluent concentration (expressed as initial percentages) for each acclimation stage of the membrane bioreactor system to which the adsorbent material is added, i.e., stage a before the addition of adsorbent material, stage B during the acclimation period, and stage C after acclimation.

Each influent wastewater may be deficient in certain nutrients that are biologically beneficial to be present in bioreactor 202. In addition, some influent wastewater may have a pH of peracid or overbase. As such, phosphorus, nitrogen, and pH adjusting materials or chemicals may be added to maintain optimal nutrient ratios and pH values within bioreactor 202 for biological life and related activities, including biological oxidation, as will be apparent to those skilled in the art.

Effluent from bioreactor 202 is directed through separation subsystem 222 to membrane operating system 204 inlet 210. Such transferred mixed liquor that has been treated in bioreactor 202 is substantially free of adsorbent material. In the membrane operating system 204, the wastewater is passed through one or more microfiltration or ultrafiltration membranes, thereby removing or reducing the need for clarification and/or third filtration. The membrane permeate, i.e., the liquid that passes through membrane 240, is discharged from membrane operating system 204 via outlet 212. The membrane retentate, i.e., the solids from the bioreactor 202 effluent, including activated sludge, is returned to the bioreactor 202 via return activated sludge line 214.

Spent adsorbent material, such as granular activated carbon, from the bioreactor 202, which is no longer effective at adsorbing contaminants, such as certain compounds that are all resistant to biological decomposition, biologically refractory compounds, and biologically inhibitory compounds, can be removed through the mixed liquor waste discharge port 216 of the bioreactor 202. A waste outlet 218 may also be connected to return pipe 214 to dispose of some or all of the returned activated sludge, for example to control the mixed liquor and/or culture concentration. Sludge is discharged from the waste activated sludge-bearing plant when it increases to a point where the mixed liquor solids concentration is too high and thus disrupts the operation of a particular membrane bioreactor system. In addition, the mixed liquor waste discharge port 216 can be used to remove portions of the adsorbent material, thereby removing certain portions of the biologically refractory compounds, bio-inhibitory compounds, and/or organic and inorganic compounds that are all resistant to biological decomposition, rather than from a return activated sludge line with waste activated sludge, resulting in lower concentrations of these biologically refractory compounds, bio-inhibitory compounds, and/or organic and inorganic compounds that are all resistant to biological decomposition in the effluent, and more stable biomass within the membrane bioreactor. An equal amount of fresh or regenerated adsorbent material may be added.

The preliminary screening and/or separation system 220 may be disposed upstream of the inlet 206 of the bioreactor 202. The primary screening and/or separation system may include a dissolved oxygen flotation system, a coarse screen, or these and/or other primary treatment devices of the type known in the art for separating suspended matter. Optionally, the primary screening and/or separation system 220 may be eliminated, or other types of primary treatment devices may be included, depending on the particular wastewater being treated.

To prevent at least a majority of the adsorbent material 234 from entering the membrane operating system 204 and causing undesirable abrasion and/or fouling of the membrane 240, a separation subsystem 222 is provided. As shown, in FIG. 2, separation subsystem 222 is located proximal to the outlet of bioreactor 202. In certain embodiments, however, separation subsystem 222 may be located in a separate vessel downstream of bioreactor 202. In either case, the separation subsystem 222 includes devices and/or structures to prevent contact between at least a majority of the adsorbent 234 and the membrane operating system 204. Separation subsystem 222 may include one or more of a screening device, a deposition section, and/or other suitable separation device.

Suitable types of screens or screening devices for use in certain embodiments of the invention include wedge wire screens, metal or plastic apertured plates, or woven fabrics, in cylindrical or flat configurations and arranged at various angles, including vertically oriented, horizontally oriented, or any angle therebetween. In additional embodiments, an active screening device, such as a rotary drum screen, a shaker screen, or other mobile screening device may be employed. In general, the system used for the other separation subsystems 222 is a screening device system having a mesh size less than the lower limit of the effective particle size of the adsorbent material used.

Other types of separation subsystems may be used in place of or in combination with the screening apparatus. For example, as described in more detail below, a deposition zone may be provided in which the adsorbent material is deposited by gravity.

In other embodiments, or in combination with the preceding embodiments, the separation subsystem may include a centrifugal system (e.g., hydrocyclone, centrifuge, etc.), an aerated grit chamber, a flotation system (such as induced gas flotation or dissolved air), or other known devices.

Optionally, or in combination with a separation subsystem 222 at the proximal end of the outlet of bioreactor 202, the separation subsystem may be located between bioreactor 202 and membrane operating system 204 (not shown). Such alternative or additional separation subsystems may be the same as or different from separation subsystem 222 in terms of type and/or size. For example, in certain embodiments, a settling section, a clarifier, a hydrocyclone separator, a centrifuge, or a combination thereof may be provided to operate as a separate unit between the bioreactor 202 and the membrane operating system 204.

Note that the separation subsystem 222 is highly effective for preventing passage of its original size adsorbent material to the membrane operating system. In certain preferred embodiments, the separation subsystem 222 prevents substantially all of the adsorbent material 234 from passing to the membrane operating system 204. However, during operation of the system 200, various causes of attrition of the adsorbent material, including inter-particle collisions, shearing, circulation, or particle impingement within stationary or moving equipment, may result in particle formation that is too small to be effectively retained in the separation subsystem 222. To reduce damage to the membrane and waste from adsorbent material consumption, certain embodiments include a separation subsystem 222, which separation subsystem 222 prevents passage of substantially all of the adsorbent material 234 in the range of about 70% to about 80% of its original size. The percentage reduction of the initial size that is acceptable can be determined by one skilled in the art, for example, based on economic evaluation. If the reduction in size results in an increase in particle flux screening systems, the film will exhibit increased erosion. As such, a cost-benefit analysis can be used to determine which is an acceptable percentage reduction of adsorbent material based on the cost of abrasion versus the final replacement of the membrane, the cost associated with reducing damaged adsorbent material, and the processing and operating costs associated with the separation subsystem that can prevent particles that are much smaller than the original adsorbent material particles or particles from passing through. Furthermore, in certain embodiments, it is desirable that some degree of inter-particle collisions, or particle impact inside the stationary or moving equipment, strip off excess biomass from the outer surface of the adsorbent material.

The mixed liquor effluent from bioreactor 202 that has been screened or separated may be pumped or otherwise moved by motive flow (depending on the design of the particular system) into membrane operating system 204. In systems using an external separation subsystem (not shown), the apparatus is preferably configured to allow the adsorbent material from the mixed liquor separation to fall back into bioreactor 202 by gravity through an external fine mesh screen or separation subsystem.

Adsorbent material, such as granular activated carbon, for example, suitably pre-wetted to form an adsorbent material slurry, may be added to the wastewater at various points of the system 200, for example, from an adsorbent material source 229. As shown in fig. 2, the adsorbent material may be introduced into one or more locations 230a, 230b, 230c and 230 d. For example, the adsorbent material may be added to the feed stream downstream of the preliminary screening system 220 (e.g., location 230 a). Optionally, or in combination, the adsorbent material may be added directly to bioreactor 202 (i.e., location 230 b). In certain embodiments, the adsorbent material may be introduced through return activated sludge line 214 (e.g., location 230 c). In additional embodiments, it may be desirable to add adsorbent material upstream of the preliminary screening system 220 (e.g., location 230d), where the preliminary screening system 220 is specifically designed for this application, by including screening to allow passage of adsorbent material through and into the bioreactor 202. The mixed liquor passes through the separation subsystem 222 and the adsorbent material is substantially prevented from entering the membrane operating system 204 with mixed liquor suspended solids.

When the adsorbent material is left in the system and exposed to wastewater constituents, including biologically refractory compounds, biologically inhibitory compounds, and/or organic and inorganic compounds that are all resistant to biological decomposition, some or all of the adsorbent material becomes ineffective for treating the wastewater constituents, i.e., the adsorption capacity decreases. This results in a higher concentration of these components entering membrane operating system 204 where they pass through the membrane and are discharged with membrane effluent 212. In addition, the adsorbent material is rendered ineffective by coating with bacteria, polysaccharides and/or extracellular polymeric substances. This coating may be to the extent of blocking the location of the orifice, thereby preventing access to biologically intractable compounds, biologically inhibitory compounds, and/or organic and inorganic compounds that are all resistant to biological decomposition, and as a result, interfering with adsorption and inhibiting biological decomposition. In certain embodiments of the invention, this coating may be removed by shear generated by one or more mechanisms in the system, such as collisions between particles of adsorbent material suspended in the mixed liquor or shear forces associated with the suspension and/or movement of the adsorbent material.

When the adsorbent material has lost all or part of its effectiveness in reducing biologically refractory compounds, biologically inhibitory compounds, and/or organic and inorganic compounds that are all resistant to biological decomposition, a portion of the adsorbent material can be discarded through the waste port 216, such as by discharging a portion of the mixed liquor containing the adsorbent material dispersed therein.

As previously described, additional fresh or regenerated adsorbent material may be introduced into the system through adsorbent material introduction device 229 and/or at one or more suitable addition locations. The influent and effluent wastewater COD compound concentrations and/or inorganic compound concentrations can be monitored to determine when the adsorbent material and its attendant biomass within the system has suffered a decrease in effectiveness. A plot of the difference between influent COD and effluent COD divided by influent COD concentration will show the diminishing loss of effectiveness of the adsorbent material in the mixed liquor. The same type of mapping can be used to monitor the inorganic removal capability of the system. The COD removal amount from the feed stream may provide the relative amount of biologically refractory compounds and/or biostatic compounds removed from the wastewater feed. When the system operator has experience with treating a particular wastewater, it will be possible to determine when this ratio indicates a point in time at which it is desired to remove a portion of the adsorbent material within the bioreactor and replace it with fresh adsorbent material. The desired efficacy of the system for biologically refractory compounds, biologically inhibitory compounds, and/or organic and inorganic compounds that are completely resistant to biological decomposition will be regained, for example, by producing effluent streams that meet regulatory requirements. Sampling and analyzing the effluent for specific organic and inorganic compound concentrations can also be used to determine when the adsorbent material and its attendant biomass within the mixed liquor has suffered a decrease in effectiveness and must begin partial replacement.

An operator of a membrane bioreactor system 200 according to the present invention may begin to replace a portion of the adsorbent material as certain organic or inorganic compounds of the effluent water begin to approach the emission concentration of these compounds allowed by the facility. The allowable emission concentrations are typically limited by the facility's license, such as determined by the national pollutant emission removal system (NPDES) license program as set forth by the united states environmental protection agency, or by similar governing bodies in a particular state or country. As the operator gains experience in operating such a system with their particular wastewater, it will be expected when replacement of the adsorbent material should begin. When the operator determines that the efficacy of the adsorbent material and its accompanying biomass approaches the contaminant concentration of the effluent that is not satisfactory, normal disposal of excess biomass performed by disposing of the returned activated sludge from the line 218 may be stopped, with the excess biomass and accompanying adsorbent material being disposed of from the bioreactor 202 through the waste port 216. The amount of waste material is determined by the requirement to maintain mixed liquor suspended solids within the optimum operating range for the particular membrane bioreactor system. After replacement of a portion of the adsorbent material, the effluent is monitored by an operator to determine whether the desired contaminant removal efficiency has been restored. Additional changes may be made as needed based on operational experience.

In certain implementations, the system and/or individual devices of the system can include a controller to monitor and adjust the system, if desired. The controller may direct any parameters within the system in accordance with desired operating conditions, such as based on government regulations regarding effluent flow. The controller may associate each potential flow adjustment or regulation valve, feeder, or pump based on one or more signals generated by sensors or timers located within the system or individual devices. The controller may also associate each potential flow adjustment or regulation valve, feeder, or pump based on one or more signals generated by sensors or timers located within the system or individual devices that indicate a particular trend, such as an upward or downward trend in the characteristics or properties of the system over a predetermined period of time. For example, a sensor in the effluent stream may generate a signal indicating that a concentration of a contaminant, such as a biologically refractory compound, a biologically inhibitory compound, and/or an organic and inorganic compound that is totally resistant to biological decomposition, has reached a predetermined value or trend, or is indicative of a COD level, thereby triggering the controller to perform certain actions from or at the sensor, either upstream or downstream of the sensor. This action may include any one or more of removing adsorbent material from the bioreactor, adding new or regenerated adsorbent material to the bioreactor, adding different types of adsorbent material, adjusting the flow of wastewater at the feed inlet or the inlet of any device within the system, diverting the flow of liquid to the feed inlet or the inlet of any device within the system to a storage tank, adjusting the flow of gas within the bioreactor, adjusting the residence time within the bioreactor or other device, and adjusting the temperature and/or pH within the bioreactor or other device. One or more sensors may be used with one or more devices or flows of the system to provide an indication or characteristic of the status or condition of any one or more processes performed at the system.

The system and controller of one or more embodiments of the present invention provide a diversified unit with multiple modes of operation that can increase the efficiency of the wastewater treatment system of the present invention in response to multiple input signals. The controller may be implemented using one or more computer systems, which may be, for example, a general purpose computer. In addition, the computer system may include specially-programmed special-purpose hardware, such as an application-specific integrated circuit (ASIC) or a controller intended for use in a water treatment system.

The computer system may include one or more processors, typically coupled to one or more storage elements, which may include, for example, any one or more of a hard disk memory, flash memory elements, RAM memory elements, or other components to store data. Memory is typically used for storing programs and data during system operation. For example, the memory may be used to store historical data relating to the parameters over a period of time and operational data. Software, including program code that implements embodiments of the invention, can be stored on a computer-readable and/or writable non-volatile recording medium and then typically copied into memory where it can then be executed by one or more processors. Such program code may be written in any one or combination of a variety of program languages.

The components of the computer system may be coupled to one or more interconnection mechanisms, which may include one or more buses between the components, e.g., integrated within the same device, and/or a network of components, e.g., residing in separate discrete devices. The interconnection mechanism typically allows communication, for example, data and commands to be exchanged between components of the system.

The computer system also includes one or more input devices, such as a keyboard, mouse, trackball, microphone, touch panel, and other human interface devices, and an output device, such as a printing device, display screen, or speaker. In addition, a computer system may contain one or more interfaces that may connect the computer system to a communications network, either in addition to or in place of a network that may be formed by one or more components of the system.

According to one or more embodiments of the present invention, one or more input devices may include sensors to measure any one or more parameters of the system and/or its components. Additionally, one or more of the sensors, pumps, or other components of the system, including metering valves or dosers, may be connected to a communication network operatively coupled to the computer system. Any one or more of the foregoing may be coupled to another computer system or component to communicate with the computer system via one or more communication networks. This configuration allows any sensor or signal generating device to be located at a significant distance from the computer system and/or any sensor to be located at a significant distance from any subsystem and/or controller while still providing data therebetween. Such communication mechanism may be performed by utilizing any suitable technique including, but not limited to, utilizing a wireless communication protocol.

While the computer system is illustrated as one type of computer system that can implement aspects of the present invention, it should be understood that the present invention is not limited to implementation in software or to the computer system illustrated. Indeed, rather than being implemented on a general purpose computer system, for example, the controller or components thereof or subsections thereof may alternatively be implemented as a dedicated system or dedicated Programmable Logic Controller (PLC) or implemented in a distributed control system. Still further, it should be understood that one or more features or aspects of the present invention may be implemented in software, hardware, or firmware, or any combination thereof. For example, one or more segments of the algorithm executable by the controller may be executed on separate computers, which in turn may communicate over one or more networks.

In certain embodiments, one or more sensors may be included at locations throughout the system 200 that communicate with a human operator or an automated control system to implement appropriate process modifications in the programmable edit control membrane bioreactor system. In one embodiment, the system 200 includes a controller 205, which may be any suitably programmed or dedicated computer system, PLC, or distributed control system. The concentration of certain organic and/or inorganic compounds may be determined in membrane operating system effluent 212 or in the effluent from outlet 208 of bioreactor 202, as indicated by the dashed connection between controller 205 and both effluent line 212 and the intermediate effluent line between outlet 208 and inlet 210. In another embodiment, the concentration of volatile organic compounds or other properties or characteristics of the system may be determined at one or more of the inlets 201, 206, or 210. Sensors known to those skilled in the art of process control equipment include laser-induced fluorescence based sensors or any other sensor suitable for in situ real-time monitoring of the concentration of organic or inorganic compounds or system characteristics in the effluent. Sensors that can be used include immersion sensors for oil-in-water measurements that use UV fluorescence for detection, such as the environment-friendly fluorescence (enviroFlu) -HC sensor from sister-in-law oes optical sensors (TriOS optical sensors), orleburg, germany. The sensor may include a lens that is coated or otherwise treated to prevent or limit the amount of fouling or filming that occurs on the lens. When one or more sensors in the system generate a signal that the concentration of one or more organic and/or inorganic compounds exceeds a predetermined concentration, the control system can perform a responsive action, such as an appropriate feedback action or forwarding action, including but not limited to removal of the adsorbent material through the waste discharge port 216 (as indicated by the dashed link between the controller 205 and the waste discharge port 216); adding new or regenerated adsorbent material through the adsorbent material introduction device 229 or at one of the other locations (as indicated by the dashed connection between the controller 205 and the adsorbent material introduction device 229); adding different types of adsorptive materials; modifying the water retention time; modifying biological characteristics such as simple carbon foods for microorganisms or adding phosphorus, nitrogen, and/or pH adjusting chemicals; and/or other modifications as previously described or apparent to those skilled in the art.

Note that although the controller 205 and the adsorbent material introduction device 229 are shown only with respect to fig. 2, it is contemplated that these features and multiple feedback and forwarding capabilities may be incorporated into any of the systems described herein. In addition, the controller 205 may be electrically coupled to other components, such as a wastewater feed pump and suspension system 232.

After the mixed liquor is aerated and treated by the adsorbent material in bioreactor 202, the treated mixed liquor is transported to membrane operating system 204 through separation subsystem 222, and substantially free of adsorbent material. The separation subsystem 222 prevents adsorbent material from entering the membrane operating system 204. By maintaining the adsorbent material in bioreactor 202, or upstream of membrane operating system 204, the methods and systems of the present invention reduce or eliminate the chance of fouling and/or abrasion of the membrane operating system tank by the adsorbent material.

Membrane operating system 204 contains filtration membrane 240 from biomass and any other solids in the mixed liquor in effluent filtration membrane operating system tank 204 from bioreactor 212. As known to those skilled in the art, these membranes 240 may be hollow fiber membranes or other suitably configured configurations, typically very expensive and highly desirable to protect the membrane from damage to maximize its useful life. In the methods and systems of the present invention, the membrane life of the operating system tank is extended because the separation subsystem 222 substantially reduces or eliminates the entry of adsorbent materials, such as granular activated carbon and/or any other solid particles and particulates, into the membrane operating system 204.

The outlet 212 transports the filtered effluent from the membrane operating system tank 204. A return activated sludge line 214 transports the return activated sludge from the membrane operating system tank 204 to the bioreactor 202 for further treatment of the wastewater feed stream. Excess sludge is discarded from the system using waste line 218 as in conventional membrane bioreactor systems.

In systems where bioreactor 202 is an aerobic reactor, such as an aeration tank, and the microorganisms are aerobic microorganisms, an air diffuser or mechanical mixing system may be used to maintain the adsorbent material in suspension. As will be described in detail below, additional embodiments of the present invention include an alternative or supplemental suspension device or system 232 to maintain the adsorbent material in suspension.

Maintaining a relatively large adsorbent material particle suspension typically requires significantly more energy than prior art systems that do not use adsorbent materials or that employ powdered activated carbon. Nonetheless, advantages of using adsorbent material particles in accordance with the present invention include increasing the rate and extent of contaminant removal, thereby reducing or eliminating the need for further downstream processing, balancing any increase in the benefits over the amount of energy consumed to operate the system.

In certain embodiments of the present invention, the suspension system 232 utilizes one or more of jet mixing, mechanical mixing, jet aeration, coarse bubble aeration, and other types of mechanical or air suspension to maintain the adsorbent material 234 in suspension while reducing abrasion of the adsorbent material 234.

In certain embodiments, after an initial period in which the adsorbent material 234 is broken within the bioreactor 202 and a portion of the particles, a portion of the rough and/or protruding surface of the adsorbent material 234 breaks down to become a powder, fines, needles, or other small particles, the adsorbent material 234 is maintained in suspension stabilization by the spray suspension system 232 such that little or no further breakage or size degradation occurs.

In other embodiments of the invention, the material may be pretreated by removing the easily damaged portion of the adsorbent material prior to introducing the adsorbent material into the system, thereby reducing the formation of fines and other undesirable small particles that are difficult to separate and may abrade the film. The pre-treatment may be carried out together with or prior to pre-wetting, for example, in a suitable conditioning apparatus such as a wet or dry particle tumbling apparatus.

The concentration of adsorbent material in the mixed liquor is generally dependent upon the particular system parameters and the particular combination of wastewater, biologically refractory and/or biologically inhibitory organic or inorganic compounds to be treated to meet the discharge requirements of the plant. Tests have indicated that operating a membrane bioreactor with a typical industrial mixed liquor suspended solids concentration (in the normal range for the particular membrane bioreactor configuration employed) and an adsorbent material concentration such as granular activated carbon of about 20% of the total mixed liquor suspended solids concentration is sufficient to remove biologically refractory and/or biostatic compounds present in the wastewater feed without fouling the screening system used. Higher concentrations of adsorbent materials may be added to provide additional safety against process upsets that may result in higher than normal effluent concentrations of biologically intractable compounds, biostatic compounds, and/or organic and inorganic compounds that are all resistant to biological decomposition. Note that such additional adsorbent material would result in increased screening and/or deposition requirements. Based on experience or otherwise based on the safety margin desired against process upsets, the minimum concentration of adsorbent material available to still achieve the desired effluent quality can be determined experimentally, as deemed appropriate for the particular system and method.

The present invention uses adsorbent material upstream of the membrane operating system tank to adsorb organic and inorganic materials (biologically refractory, biostatic, or otherwise), and provides for the use of suspended media membrane bioreactors in a variety of different configuration configurations. In addition, various separation devices may also be used to maintain the adsorbent material in the bioreactor. It will be apparent to those skilled in the art that different systems will have different economic benefits based on the individual characteristics of the wastewater and the area in which the facility is to be erected.

Factors that are controlled to produce optimal processing conditions include the type of adsorbent material, including its size, shape, hardness, specific gravity, deposition rate, required air flow rate, or other suspension requirements for the particles suspended in the mixed liquor, i.e., maintaining the granular activated carbon as a suspension medium, the bar screen spacing or opening size and hole configuration, the concentration of adsorbent material in the mixed liquor, the mixed liquor volatile suspended solids concentration, the total mixed liquor suspended solids concentration, the ratio of the returned activated sludge flow rate divided by the mixed liquor flow rate into the membrane operating system tank, the water residence time, and the sludge residence time. Such optimization provides biologically refractory compounds, readily decomposable biological oxygen demand compounds (BOD)₅) Some of the bio-inhibitory compounds, organic or inorganic compounds that are all resistant to biological decomposition, and extracellular polymeric substances are adsorbed by an adsorbent material such as granular activated carbon suspended in the mixed liquor.

Another effect of the apparatus of the present invention provides a location to which microorganisms in the mixed liquor suspended solids can adhere. This aspect of the method produces a mixed liquor volatile suspended solids stream that is more stable and more resilient to disturbance conditions than membrane bioreactors operating with similar water and sludge retention times but without granular activated carbon reinforcement, and allows for the promotion of the biodegradation of organic matter present in the wastewater. In the event that the upstream process perturbations result in the depletion of some viable microorganisms that auto-float in the mixed liquor, the source of microorganisms within or on the surface of the porous space of the adsorbent material is used as an inoculum source. In the case of thermal shock or toxic chemical impact systems, some bacteria will die in conventional systems, while some microorganisms inside or on the surface of the pore space may survive, thus requiring only a partial recovery time compared to conventional systems that do not contain an adsorbent. For example, in systems where the bacteria are mesophilic, the adsorbent may allow some of the bacteria inside the pore sites to survive thermal shock caused by the temperature rise. Similarly, in systems where the bacteria are thermophilic, the adsorbent may allow some of the bacteria inside the pore locations to survive thermal shock due to the temperature drop. In both cases, the time required for the culture to re-acclimate is greatly reduced. Furthermore, in the case of a system-impact-destroying all or part of the microorganism population, the presence of the adsorbent material allows for sustained operation in which unstable, intractable, and inhibitory contaminants can be adsorbed and simultaneously modulate the microorganism population.

The various effects result in a more rapid acclimation of the mixed liquor to the wastewater feed, reduced fouling of the membrane, improved tolerance to feed concentration and flow rate, manufacture of sludge with faster dewatering, more manageable with less oil properties, and a bleed stream with lower concentrations of organic and inorganic impurities than can be obtained with conventional membrane bioreactor devices.

The use of adsorbents such as granular activated carbon instead of powdered activated carbon may eliminate membrane fouling and/or erosion problems that have been identified in powdered activated carbon membrane bioreactor testing.

Although the use of granular activated carbon instead of powdered activated carbon does not use carbon equally effectively on a weight basis, the methods and systems of the present invention substantially prevent the granular activated carbon from entering the membrane operating system, thereby reducing or eliminating the chance of membrane erosion and fouling. But the impact on the decrease of the adsorption efficiency caused by the use of granular activated carbon instead of powdered activated carbon does not significantly affect the overall efficiency of the membrane bioreactor device reinforced by activated carbon.

Tests have indicated that the primary mechanism for removing certain biostatic and/or biostatic compounds involves the extended residence time of the biostatic and/or biostatic compounds exposed to microorganisms in a powdered activated carbon enhanced device. Microorganisms in the mixed liquor volatile suspended solids adsorbed on the adsorbent material, such as granular activated carbon, have a longer time to digest these certain biologically refractory and biostatic compounds. The extension of the residence time for biological decomposition has been shown to be a major factor in reducing the concentration of certain biologically refractory and biostatic compounds in membrane bioreactor effluent and to not require the higher adsorption efficiency of powdered activated carbon to achieve the desired results.

Granular activated carbon functions equally well or better than powdered activated carbon-enhanced membrane bioreactors with respect to enhancing the removal of biologically refractory compounds, biologically inhibitory compounds, organic and inorganic compounds that are totally resistant to biological decomposition, and extracellular polymeric compounds. In addition, due to the large size of the granular activated carbon, it can be effectively filtered or otherwise separated from the mixed liquor entering the membrane operating system tank. By using granular activated carbon in accordance with the present invention, the erosion that occurs when powdered activated carbon is used can be eliminated or significantly reduced.

While the use of powdered activated carbon particles in membrane bioreactors has shown some of the same advantages previously described for granular activated carbon systems, membrane erosion from powdered activated carbon in membrane operating system tanks is unacceptable because the useful life of the membrane may be shortened to unacceptable levels, e.g., significantly shorter than the warranty period of typical membranes. Since the membrane cost represents a significant portion of the total membrane bioreactor system cost, extending its useful life is an important factor in the operating cost of the membrane operating system.

FIG. 3 shows another embodiment of a membrane bioreactor system 300 operating with biological denitrification. As will be apparent to those skilled in the art, other specialized biological or chemical treatment systems required for a particular influent wastewater may also be incorporated into the system of the present invention shown generally with respect to fig. 2. The embodiment of fig. 3 is similar to the embodiment of fig. 2, but with the addition of an anoxic (low oxygen concentration) zone 331. In embodiments where an anoxic zone or vessel is used herein, the biochemical oxygen demand content of a simple organic carbon source, such as methanol, or the wastewater itself, is available for consumption by the biological organisms. The wastewater 306 is directed to an anoxic zone 331 that is in fluid communication with the bioreactor 302 containing the adsorbent material 334. The anoxic section 331 may include a mixer and/or an aeration device (not shown). In embodiments herein, wherein an aeration device is used, the dissolved oxygen concentration is controlled to maintain anoxic conditions. The effluent from bioreactor 302 is directed through separation subsystem 322 to membrane operating system 304 inlet 310. In the membrane operating system 304, the wastewater is passed through one or more microfiltration or ultrafiltration membranes, thereby eliminating or reducing the need for clarification and/or a third filtration. The membrane permeate, i.e., the liquid that passes through the membrane 340, is discharged from the membrane operating system 304 via outlet 312. The membrane retentate, i.e., the solids in the effluent from bioreactor 302, including activated sludge, is returned to anoxic zone 331 via return activated sludge line 314. The spent adsorbent material from the bioreactor 302 can be removed through the mixed liquor waste discharge port 316 of the bioreactor 302. Waste outlet 318 may also be coupled to return line 314 to divert some or all of the returned activated sludge for waste disposal, such as to control mixed liquor and/or culture concentration. The mixed liquor waste discharge port 316 can also be used to remove a portion of the adsorbent material. An equal amount of fresh or regenerated adsorbent material may be added.

As with the system described in fig. 2, a plurality of position-absorbent materials 334 may be added to the system. In a preferred embodiment, the adsorbent material is added at location 330b that prevents access to the anoxic zone 331.

Fig. 4 is a schematic illustration of a water treatment system 400, which is one embodiment of the system 100 shown in fig. 1. In system 400, bioreactor 402 is divided or partitioned into a plurality of sections 402a and 402b, for example, using baffle walls 403. A membrane operating system tank 404 is located downstream of the bioreactor 402.

The water between sections 402a and 402b is engineered to provide a flow in a downstream direction. This can be accomplished by configurations and/or devices including, but not limited to, weirs, immersion ports, and/or various distribution piping configurations for the purpose of maintaining a positive separation between sections 402a and 402b, and adsorbent material 434 only in section 402 b. These various configurations may also be designed to control the flow rate between sections 402a and 402 b. Other specific configurations are not illustrated as they are known to those skilled in the art.

During operation, influent wastewater stream 406 is directed to bioreactor 402, and specifically to first section 402a of bioreactor 402. As previously discussed, it will be apparent to one skilled in the art that phosphorus, nitrogen, and pH adjusting materials or chemicals may be added to maintain the biological life and associated activity of the first section 402a, including optimal nutrient ratios and pH values for biological oxidation. The microbially decomposable mixed liquor of first zone 402a suspends at least a portion of the biologically labile content of solids. The mixed liquor suspends simple carbon in solids, i.e., biologically labile compounds, which are used as a food source for microorganisms. The wastewater may be treated in section 402a to remove substantially all of the biologically labile content of mixed liquor suspended solids, or in some embodiments, a portion of the biologically labile content of mixed liquor suspended solids may be retained for sending to biological reaction section 402 b. In embodiments where the biologically unstable content of mixed liquor suspended solids falls in section 402a to a level insufficient to effectively support downstream microorganisms, one or more controls are implemented to maintain an effective concentration of microbial food sources, particularly in downstream bioreaction section 402 b. This control may be based, for example, on the residence time of the wastewater in the upstream section 402a, slipstream of untreated influent wastewater to section 402b, control of return activated sludge, introduction of methanol or other simple carbon food source for microorganisms, or provide intermittent aeration in section 402a, or other means of promoting healthy biomass in section 402 b.

The adsorbent material 434 is maintained in suspension in the biological reaction zone 402b using a suspension device 432, which may comprise one or more of the suspension systems described herein, such as shown in fig. 7, 8, 9, 10, 11, or 12, the systems of the examples herein, or any suitable conventional device for circulating air, liquid, or a combination of air and liquid. Such conventional devices include, but are not limited to, air diffusion bubblers, paddles, mixers, surface aerators, liquid circulation pumps, and other devices known to those skilled in the art. It should be understood that while in certain embodiments it is desirable to use a relatively low energy consumption to maintain the adsorbent material 434 in suspension in the suspension device 432, such as that shown in association with fig. 7, 8, 9, 10, 11 or 12 or described in example 3, example 4 or example 5, other embodiments using less efficient devices are also suitable because the total volume of the section 402b in which the adsorbent material 434 is maintained in suspension is only a fraction of the total volume of the bioreactor 402.

Screening/separation system 422 is located at section 402b to substantially prevent adsorbent material 434 from entering membrane handling system 404. In certain embodiments, the adsorbent material is added only at location 430b, i.e., the corresponding location of section 402 b.

Note that while system 400 is shown as a biological reaction zone that is substantially free of adsorbent, and a zone that contains adsorbent material 434, those skilled in the art will appreciate that fewer or more of each type of zone may be used. The concentration of the adsorbent material 434 in section 402b can be, for example, the same concentration used in the system of fig. 1, or higher or lower concentrations can be used depending on the wastewater being treated.

In addition, the bioreaction sections may be formed in a variety of configurations. For example, in a prismatic bioreactor tank, dividing walls may be provided across the width of the tank to divide the tank into sections. For example in a cylindrical trough, a dividing wall may be provided as a chord, or a plurality of walls may be provided, for example in the form of radii, forming two or more sectors.

With the adsorbent material only in the lifetime biological reaction zone, the biologically labile compound can be treated in an upstream zone that is free of adsorbent material, thus eliminating the need for suspending the adsorbent material in a mixed liquor of the adsorbent-free zone of the system 400. This also allows the development of a microbial community that can biodegrade at least some of the intractable and/or biostatic compounds that cannot be biodegraded by conventional microorganisms present in the upstream sections of the system. It will also be appreciated by those skilled in the art that a system like system 400 according to the present invention may be provided using separate tanks rather than divided sections of a bioreactor, as schematically shown in fig. 6, or a combination of divided sections of a bioreactor and separate vessels.

Still referring to fig. 4, the effluent from the biological reaction section 402b is directed through the screening separation/separation system 422 to the inlet 410 of the membrane operating system 404. In membrane operating system 404, wastewater is passed through one or more microfiltration or ultrafiltration membranes 440, membrane permeate is discharged through outlet 412, and membrane retentate, including activated sludge, is returned to biological reaction zone 402a via return activated sludge line 414.

The spent adsorbent material from the biological reaction zone 402b can be periodically removed through a mixed liquor waste discharge port 416. Waste outlet 418 may also be coupled to return activated sludge line 414 to divert some or all of the return activated sludge for disposal, such as to control mixed liquor and/or culture concentration. The mixed liquor waste discharge port 416 can also be used to remove a portion of the adsorbent material. An equal amount of fresh or regenerated adsorbent material may be added.

FIG. 5 shows a system 500 operating in a similar manner to system 400, with a bioreactor 502 divided into a plurality of sections 502a and 502b, and including a biological denitrification step integrated with bioreactor 502. In this embodiment, the adsorbent material 535 addition, e.g., position 530b, is maintained in suspension in zone 502b without introduction of the anoxic zone 531 or zone 502 a.

Effluent from the biological reaction section 502b is directed through the screening separation/separation system 522 to the inlet 510 of the membrane operating system 504. In the membrane operating system 504, the wastewater passes through one or more microfiltration or ultrafiltration membranes 540, the membrane permeate is discharged via outlet 512, and the membrane retentate, including activated sludge, is returned to the anoxic section 531 via return activated sludge line 514.

The spent adsorbent material from the biological reaction zone 502b can be periodically removed through the mixed liquor waste discharge port 516. A waste outlet 518 may also be coupled to return activated sludge line 514 to divert some or all of the return activated sludge for disposal, such as to control mixed liquor and/or culture concentration. The mixed liquor waste discharge port 516 can also be used to remove a portion of the adsorbent material. An equal amount of fresh or regenerated adsorbent material may be added.

Under certain operating conditions, it may be desirable to introduce a simple organic carbon source, such as methanol, into the anoxic zone to assist in the denitrification process. In addition, the biological oxygen demand content of the raw wastewater typically provides a source of food for consumption by the biological organisms.

In additional embodiments, the anoxic segment may be disposed downstream of segment 502b (not shown) or between segments 502a and 502 b. In either case, it may be desirable to add food consumed by the biological organism to originate from the anoxic zone to assist in the denitrification process.

It will also be appreciated by those skilled in the art that a system similar to system 500 according to the present invention may be provided using separate tanks rather than divided sections of a bioreactor, as schematically shown in fig. 6, or a combination of divided sections of a bioreactor and separate vessels.

Fig. 6 is a schematic illustration of another embodiment of a wastewater treatment system 600. In system 600, a train of bioreactors is provided, including a first bioreactor 602a that is substantially free of adsorbent material, and a second bioreactor 602b that contains a suspension of adsorbent material 634 that may be added, for example, at one or both of locations 630a and 630 b. Membrane operating system 604 is located downstream of bioreactors 602a and 602 b. Second bioreactor 602b includes a screening/separation system 622 located at section 602b to substantially prevent adsorbent material from entering membrane operating system 604.

The water flow between reactors 602a and 602b is engineered to provide flow in a downstream direction to maintain the adsorbent material only in section 602b, i.e., to prevent the adsorbent material from flowing back from reactor 602b to reactor 602a, and may be designed to control the flow rate between sections 602a and 602 b.

During operation, influent wastewater stream 606 is directed to bioreactor 602 a. Microorganisms in first bioreactor 602a may break down at least a portion of the biologically labile compounds contained in the mixed liquor suspended solids. Simple organic matter in the mixed liquid suspended solid is used as a food source of the microorganism. The partially treated wastewater is sent to bioreactor 602b via conduit 607. The partially treated wastewater from bioreactor 602a may also be gravity fed to bioreactor 602b, or transported by other means known to those skilled in the art.

The wastewater may be treated in first bioreactor 602a to remove substantially all of the biologically labile compounds of the mixed liquor suspended solids, or in some embodiments, a portion of the biologically labile compounds contained in the mixed liquor suspended solids may be retained for feeding to second bioreactor 602 b. In embodiments where the mixed liquor suspended solids contain biologically labile compounds that are reduced to a level insufficient to support downstream microorganisms in first bioreactor 602a, one or more controls are implemented to maintain an effective concentration of microbial food sources, for example, in downstream bioreactor 602 b. This control may be, for example, based on the residence time of the wastewater in the downstream bioreactor 602a, slipstream of untreated influent wastewater to the bioreactor 602b, control of the return activated sludge, introduction of methanol or other simple carbon food source for microorganisms, or other suitable return or forward action.

Adsorbent material 634 is maintained in suspension in bioreactor 602b using suspension device 632, which may comprise one or more of the suspension systems described herein, such as shown in fig. 7, 8, 9, 10, 11, or 12, the systems of the examples herein, or any suitable conventional device for circulating air, liquid, or a combination of air and liquid. Such conventional devices include, but are not limited to, air diffusion bubblers, paddles, mixers, surface aerators, liquid circulation pumps, and other devices known to those skilled in the art. It should be understood that while in certain embodiments it is desirable to use a suspension device 632 that is relatively low energy consuming to maintain the adsorbent material in suspension, such as that shown in association with figures 7, 8, 9, 10, 11 or 12 or described in example 3, example 4 or example 5, other embodiments that are less efficient devices are also suitable because the total volume of section 602b is only a fraction of the combined total volume of bioreactors 602a and 602 b.

The screening/separation system 622 is located in the bioreactor 602b to substantially prevent the adsorbent material 634 from entering the membrane operating system 604. In certain embodiments, the adsorbent material 634 is added only to bioreactor 602b, for example at location 630a associated with conduit 607, or directly to bioreactor 602b (location 630 b). In certain preferred embodiments, the adsorbent material is pre-wetted, e.g., formed into a slurry, prior to introduction into bioreactor 602 b.

Note that while system 600 is shown as a bioreactor that is substantially free of adsorbent, and a bioreactor that contains adsorbent material 634, those skilled in the art will appreciate that fewer or more types of bioreactors, or bioreactor sections, may be employed. The concentration of adsorbent material in bioreactor 602b may be, for example, the same concentration used in the system of fig. 1, or a higher concentration may be used depending on factors including, but not limited to, the characteristics of the partially treated wastewater to be treated in bioreactor 602 b.

In addition, the bioreaction sections may be formed in a variety of configurations. For example, in a prismatic bioreactor tank, dividing walls may be provided across the width of the tank to divide the tank into sections. For example in a cylindrical trough, a dividing wall may be provided as a chord, or a plurality of walls may be provided, for example in the form of radii, forming two or more sectors. By having the adsorbent material only in the final bioreactor, the biologically labile compound can be treated in an upstream bioreactor that does not contain adsorbent material. This allows the development of a microbial community that can biodegrade biologically intractable compounds that cannot be biologically oxidized by conventional microorganisms present in the upstream sections of the system. It will also be appreciated by those skilled in the art that a system like system 600 according to the present invention may be provided using divided sections of a bioreactor rather than separate bioreactors, as schematically shown in fig. 4, or a combination of divided sections of a bioreactor and separate reactors.

Still referring to fig. 6, effluent from biological reaction zone 602b is directed through screening separation system 622 to inlet 610 of membrane operating system 604. In membrane operating system 604, wastewater is passed through one or more microfiltration or ultrafiltration membranes 640, membrane permeate is discharged through outlet 612, and membrane retentate, including activated sludge, is returned to biological reaction zone 602a via return activated sludge line 614.

The spent adsorbent material from the bioreactor 602b can be periodically removed through a mixed liquor waste discharge port 616. Waste outlet 618 may also be coupled to return line 614 to divert some or all of the returned activated sludge for waste disposal, such as to control mixed liquor and/or culture concentration.

Referring generally to fig. 7, 8, 9, 10 and 11, alternative embodiments are shown, including a jet suspension system in which mixed liquor (including MLSS containing MLVSS) and adsorbent material dispersed therein are circulated through a jet nozzle. This circulation provides intimate mixing of the adsorbent with the mixed liquor and also provides turbulence that maintains the adsorbent suspended in the bioreactor. The turbulence may be localized turbulence, such as near the nozzle orifice, causing swirling and rolling of the fluid delivered by the spray nozzle. In fig. 7, 8 and 11, the solid black units represent the adsorbent material, while the irregular linear units represent microorganisms or biomass.

FIG. 7 schematically illustrates a suspension device 732 inside bioreactor 702 (partially shown for clarity of illustration). The suspension 732 includes a spray nozzle 744 fluidly coupled to a pump 748 and a gas source 760. The gas may be an oxygen-containing gas in the case of aerobic bioreactor 702, or may be an oxygen-free or substantially oxygen-free gas in the case of anaerobic bioreactor 702.

The configuration shown in fig. 7, and in certain additional implementations described in association with fig. 8, 9 and 10, may be deployed using, for example, a commercially available vicken (Vari Cant) system from rossi siemens water technologies, inc. Other jet aeration systems may also be deployed for one or more of the systems shown with respect to fig. 8, 9, and 10. For example, a number of Systems include, but are not limited to, the jet aeration Systems commercially available from waterfall, sitafloat, iowa, usa (Fluidyne Corporation), asonella KLA, ma, usa, and delton Mixing Systems, ohio, usa.

Note that while the systems described herein with respect to fig. 7, 8, 9, 10, and 11 generally show the pumps located outside of the bioreactor tank, one skilled in the art will appreciate that one or more pumps may be located inside the tank. In other embodiments, one or more pumps may be located inside or outside the high-pressure tank to maintain positive pumping.

Furthermore, although the systems described herein with respect to fig. 7, 8, 9, 10 and 11 show substantially the entire spray nozzle positioned in the bioreactor tank for purposes of illustration, in certain embodiments, a portion of the spray nozzle may be positioned outside of the bioreactor tank with at least its outlet orifice positioned in the bioreactor tank.

Spray nozzle 744 liquid inlet 746 and outlet orifice 764 and pumping device 748 inlet 752 and outlet 754 are sized and configured to allow passage of adsorbent material and MLSS, including MLVSS. Such mixed liquor, including MLSS and a mixture of MLVSS and adsorbent material, is drawn through line 751 from outlet 750 of bioreactor 702 into inlet 752 of pumping device 748. The mixture is pumped out of pumping device 748 through outlet 754 and directed through line 755 into liquid inlet 746 which is integral with or otherwise in fluid communication with spray nozzle 744.

Simultaneously, gas 760 is directed via line 761 into a gas inlet 758 integral with or otherwise in fluid communication with spray nozzle 744, and into mixing chamber 766, where the gas expands to provide a mixed flow of kinetic energy to the mixed liquor and dispersed adsorbent material in the direction of nozzle outlet aperture 764. The expanded gas, mixed liquor and dispersed adsorbent material pass through a throat 768 having a reduced cross-sectional area in the direction of fluid flow, wherein the velocity is increased out of the outlet orifice 764. The combined flow of gas, liquid and solid particles is forced into bioreactor 702, while in the continuous operation case, the solid particles of adsorbent material are maintained in suspension due to the turbulent flow of the liquid of bioreactor 702.

Referring now to fig. 8, another embodiment of a bioreactor including a jet suspension system is shown. Specifically, bioreactor 802 includes a jet suspension system 832 including a jet nozzle 844 having at least one outlet orifice 864 positioned in bioreactor 802 for circulating mixed liquor having adsorbent material dispersed therein. Spray nozzles 844 are fluidly coupled to a pump 848 to circulate mixed liquor with adsorbent material dispersed therein to create a turbulent flow that maintains the adsorbent material in suspension. As is known to those skilled in the art, any jet mixer, sprayer, or other device that can direct and discharge the mixed liquid with the adsorbent material dispersed therein without the need for an air inlet can be used as the jet nozzle 844.

In aerated bioreactor 802, a source of oxygen-containing gas, such as a conventional air diffusion device, is also provided (not shown).

The liquid inlet 846 and outlet orifice 864 of the injection nozzle 844, and the inlet 852 and outlet 854 of the pumping device 848 are sized and configured to allow passage of adsorbent materials and mixed liquor suspended solids, including mixed liquor suspended volatile solids, therethrough. Thus, mixed liquor comprising MLSS and a mixture of MLVSS and adsorbent material is drawn through line 851 from outlet 850 of bioreactor 802 into inlet 852 of pumping apparatus 848. The mixture is pumped out of the pumping device 848 via an outlet 854 and directed through a line 855 to a liquid inlet 846 that is integral to or otherwise in fluid communication with the injection nozzle 844. The spray nozzle 844 includes a throat 868 of reduced cross-sectional area in the direction of fluid flow, wherein the mixed liquor and adsorbent material are accelerated out of the outlet orifice 864.

Referring generally to fig. 9, 10 and 11, another embodiment is shown including a jet suspension system in which mixed liquor and/or return activated sludge is circulated through a jet nozzle that is free of adsorbent material. This circulation provides intimate mixing of the adsorbent material and the mixed liquor at the outlet of the spray nozzle and also provides turbulence to maintain the adsorbent material in suspension within the bioreactor. The turbulence may be localized turbulence, such as near the injection nozzle, causing swirl and roll of the fluid exiting the injection nozzle 844.

Figure 9 schematically illustrates a wastewater treatment system 900 including a suspension device 932 inside the bioreactor 902 and upstream of the membrane operating system 904. The suspension 932 includes a spray nozzle 944 fluidly coupled to a pump 948 and a source of pressurized gas 960.

System 900 includes a screening/separation system 922 that prevents at least a majority of the adsorbent material from passing, for example, through outlet 908 of bioreactor 902.

In certain embodiments, mixed liquor is drawn from the effluent of bioreactor 902 via conduits 972, 970, wherein conduit 972 is located between outlet 908 of bioreactor 902 and inlet 910 of membrane operating system 904, into inlet 952 of pumping device 948. In additional embodiments, return activated sludge is drawn from conduit 914 from membrane operating system 904 into line 970 entering inlet 952 of pumping device 948. In yet another embodiment, a combined flow of effluent from bioreactor 902 and return activated sludge from membrane operating system 904 is used as the liquid to provide recycle to the pump. Liquid from the effluent and/or return activated sludge is pumped out of the pumping device 948 via line 955 and directed to a liquid inlet that is integrally formed with or otherwise in fluid communication with the spray nozzle 944. In tandem, compressed gas 960 is directed via line 961 to an inlet port that is integral with or otherwise in fluid communication with injection nozzle 944 and to mixing chamber 966, where the compressed gas expands and provides kinetic energy to the mixed liquor in the direction of outlet port 964 of the nozzle. The expanded gas and mixed liquor passes through a throat 968 having a reduced cross-sectional area in the direction of fluid flow, increases in velocity at the throat, and exits the outlet orifice 964. The combined flow of gas and liquid is forced into the bioreactor 902 and, in the case of continuous operation, the solid particles of adsorbent material are maintained in suspension due to the turbulent flow of liquid in the bioreactor 902.

Fig. 10 schematically illustrates another embodiment of a wastewater treatment system, wherein the wastewater treatment system 1000 includes a suspension device 1032 within the interior of the bioreactor 1002 and upstream of the membrane operating system 1004. System 1000 includes a screening/separation system 1022 that prevents at least a majority of the adsorbent material from passing, for example, through bioreactor 1002 outlet 1008. The suspension device includes a spray nozzle 1044 fluidly coupled to a pump 1048 to circulate the mixed liquor to create a turbulent flow that maintains the suspension of the sorbent. At aerated bioreactor 1002, a source of oxygen-containing gas (not shown) is also provided, such as a conventional air diffusion device or any number of other devices that can transfer oxygen into the mixed liquor as would be apparent to one skilled in the art.

The flow in system 1000 is similar to system 900 shown and described above with respect to fig. 9. As such, in certain embodiments, mixed liquor is drawn from the effluent of bioreactor 1002 into inlet 1052 of pumping device 1048 via conduits 1072, 1070, wherein conduit 1072 is located between outlet 1008 of bioreactor 1002 and inlet 1010 of membrane operating system 1004. In additional embodiments, return activated sludge is drawn from conduit 1014 from membrane operating system 1004 into line 1070 entering inlet 1052 of pumping device 1048. In yet another embodiment, a combined flow of effluent from bioreactor 1002 and return activated sludge from membrane operating system 1004 is used as the liquid to provide recycle to the pump.

Liquid from the effluent and/or return activated sludge is pumped out of pumping device 1048 via line 1055 and directed to a liquid inlet that is integrally formed with or otherwise in fluid communication with spray nozzle 1044. The mixed liquor passes through a throat 1068 of reduced cross-sectional area in the direction of fluid flow, increases in velocity at the throat, and exits the outlet port 1064. The liquid stream is forced into bioreactor 1002 and, under continuous operation, the solid particles of adsorbent material are maintained in suspension by the turbulent flow of liquid through bioreactor 1002.

In certain embodiments of the systems 900 and 1000, it may be desirable to design the hydraulic system of the system such that the flow rate through the pump is equal to or greater than the total flow rate through the system, i.e., as indicated by the flow rates of the influent 906, 1006 and effluent 912, 1012.

FIG. 11 schematically illustrates a suspension 1132 within the bioreactor 1102 (partially shown for clarity of illustration). The suspension 1132 includes a spray nozzle 1144 fluidly coupled to a pump 1148 and a gas source 1160. In the case of aerobic bioreactor 1102, the gas may be an oxygen-containing gas; or in the case of the anaerobic bioreactor 1102, the gas may be an oxygen-free or substantially oxygen-free gas.

Bioreactor 1102 outlet 1150 includes a screening device 1170 that prevents passage of at least a majority of the adsorbent material. A spray nozzle 1172 or other suitable means is provided to remove accumulations from screening device 1170. The spray nozzles 1172 may direct gas and/or liquid to clean the screening device. In certain embodiments (not shown), spray nozzles 1172 may be coupled to a pump and/or a compressed gas source 1160 to provide pressurized fluid to clean screening device 1170. In additional embodiments, spray nozzles 1172 can be eliminated, for example, which can prevent accumulation of adsorbent material when screening device 1170 is an active screening device, such as a rotary screen or the like.

Thus, mixed liquor containing substantially no adsorbent material, including MLSS and MLVSS, is drawn through line 1151 from outlet 1150 of bioreactor 1102 into inlet 1152 of pumping device 1148. The mixture is pumped out of the pumping device 1148 via outlet 1154 and directed through line 1155 into liquid inlet 1146, which is integral with or otherwise in fluid communication with spray nozzle 1144. At the same time, compressed gas 1160 is directed via line 1161 into gas inlet 1158, which is integral with or otherwise in fluid communication with spray nozzle 1144, and into mixing chamber 1166, where the gas expands to provide a mixed liquid stream of mixed liquid and dispersed adsorbent material with kinetic energy in the direction of nozzle outlet orifice 1164. The expanded gas, mixed liquor and dispersed adsorbent material pass through a throat 1168 having a reduced cross-sectional area in the direction of fluid flow, wherein the velocity is increased and out of the outlet orifice 1164. The combined flow of gas and liquid is forced into the bioreactor 1102, while in the case of continuous operation, the solid particles of adsorbent material are maintained in suspension due to the turbulent flow of liquid in the bioreactor 1102.

In certain embodiments of the wastewater treatment systems described herein, the systems comprise an air-lift suspension system, which may comprise one or more draft tubes or one or more other configurations. The one or more flow conduits are sized and shaped for the desired application, and the volume of the vessel, such as a bioreactor or other device, is adapted to perform one or more of suspending the adsorbent material, maintaining the adsorbent material in suspension, mixing the adsorbent material throughout the vessel, and aerating the vessel environment including aerobic microorganisms. Gas lift suspension systems can be made up of a variety of sizes and shapes, depending on the size and shape of the container placed therein. The gas lift suspension system can include one or more draft tubes located within the vessel, wherein the adsorbent material is coupled to a wastewater treatment system. As used herein, a "draft tube" may be a tube or other structure having one or more sidewalls open at both ends that, when disposed in a vessel, provides a fluid flow path and may include a suspension of solid particles, such as a suspension of adsorbent material and associated solids in air or other gas suspended in wastewater or mixed liquor.

The draft tube may be composed of any material suitable for the particular purpose, so long as it is corrosion resistant, is resistant to the constituents of the wastewater under the conditions typical for wastewater treatment, and is resistant to turbulent flow through and around the draft tube. For example, the draft tube may be made of the same material as the vessel, or may be made of other lighter and cheaper materials, such as plastics, including fiberglass reinforced plastics, polyvinyl chloride (PVC), or acrylic. The draft tube may be preformed for insertion into the vessel, or fabricated as a part of the vessel. Thus, the flow conduit can be designed to retrofit current systems. The gas lift suspension system may be supported on the vessel wall or may be supported by the vessel bottom, so long as it allows flow through and around the draft tube. Additionally, the gas lift suspension system may be supported by additional structures constructed and arranged to hold and suspend one or more draft tubes within the vessel interior.

The individual draft tubes may be sized and shaped according to the desired application, thereby suspending the adsorbent material inside the vessel and/or operating within a predetermined operating time period. The draft tube can also have a size and shape to provide a desired degree of agitation inside the draft tube to sufficiently suspend the adsorbent material inside the vessel or in an aerated vessel environment. The desired gas lift suspension system volume may be provided by a single draft tube or a plurality of draft tubes having a total volume substantially equal to the desired volume. The specific ratio of the gas lift suspension system volume to the vessel volume can be selected to provide optimal suspension of the adsorbent material inside the draft tube. The individual ducts may have cross-sectional areas of any shape, such as circular, elliptical, square, rectangular, or any irregular shape. The individual ducts may have any overall shape, such as conical, rectangular, and cylindrical. In one embodiment, the draft tube is cylindrical. The overall dimensions of the draft tube, such as length, width, and height, can be selected to provide optimal suspension of the adsorbent material inside the vessel. For example, the particular ratio of duct length to duct width or diameter is selected to achieve optimal suspension of the adsorbent material within the vessel interior. The draft tube may comprise two opposing sidewalls inside the vessel in a configuration referred to as a "trough". One or both ends of the draft tube may be constructed and arranged to assist in the flow of adsorbent material into and/or out of the draft tube. For example, the sidewall at the first end of the draft tube can include one or more openings forming a channel to allow portions of the adsorbent material, wastewater, or other contents of the vessel at or near the first end of the draft tube to enter and exit through the draft tube sidewall. The opening forming the channel can have any shape to allow the adsorbent material to be effectively suspended inside the container. For example, the openings may be triangular, square, semi-circular, or irregular. The plurality of passages may be identical to one another and disposed uniformly around the first end of the draft tube for equally distributing the flow of adsorbent material to the draft tube.

The one or more draft tubes can be located at any suitable location within the vessel so long as they provide sufficient suspension of the adsorbent material within the vessel interior. For example, a single draft tube may, but need not, be centered with respect to the vessel sidewall. Similarly, multiple draft tubes within a single vessel may be randomly positioned or positioned in a uniform pattern relative to the vessel sidewall. The multiple draft tubes within a single vessel may, but need not, be of equal volume or cross-sectional area. For example, a single vessel may comprise cylindrical, conical, and rectangular draft tubes of various heights and cross-sectional areas. In one embodiment, the vessel can have a centrally located first draft tube of a first cross-sectional area, and a plurality of second draft tubes positioned adjacent to the side walls of the vessel, wherein the second draft tubes each have a second cross-sectional area that is less than the first cross-sectional area. In another embodiment, the vessel has a plurality of identical draft tubes. In yet another embodiment, the first draft tube can be located inside the second draft tube. In this implementation, the draft tube bottoms can be aligned with one another, or can be offset from one another.

In another embodiment, the draft tube may include a baffle to facilitate suspension of the adsorbent material. The baffles may be of any size and shape suitable for the particular draft tube. For example, the baffle may be a plate adapted to be placed on the inner surface of the draft tube or a cylinder placed within the draft tube. In one embodiment, the baffle may be a solid or hollow cylinder centrally positioned inside the draft tube. In another embodiment, the baffle may be a skirt that is positioned at the first end or the second end of one or more draft tubes in the gas lift suspension system. The baffles may be made of the same material of the draft tube or of a different material compatible with the suspension system.

The vessel in which the draft tube may be located may be of any size or shape suitable for suspending adsorbent materials in association with a gas lift suspension system. For example, the container may have a cross-sectional area of any shape, such as circular, oval, square, rectangular, or any irregular shape. In some embodiments, the container may be constructed or modified to facilitate proper suspension of the adsorbent material. In certain embodiments, the container may be constructed or modified to include a sloped portion at the bottom of the container to facilitate movement of the adsorbent material toward the airlift suspension system. The incline may be at any angle relative to the bottom of the container to promote movement of the adsorbent material toward the airlift suspension system.

Referring now to fig. 12, an example airlift suspension system 1232 for maintaining adsorbent material suspended inside a vessel, such as bioreactor 1202, according to one embodiment is schematically shown. In fig. 12, the circular cells represent air bubbles, the small solid cells or dots represent adsorbent material, and the irregular linear cells represent microorganisms or biomass. The airlift suspension system 1232 includes one or more flow conduits 1292, which, as previously described, are constructed, positioned, and sized to assist in the elevation of the adsorbent material and maintain the adsorbent material in suspension. Gas enters through a gas conduit 1290 and is directed into the bottom of a flow conduit 1292 by a distribution nozzle or diffuser 1291. In certain other embodiments, gas can be directed into the bottom of the flow conduit 1292 through the apertures of the gas conduit 1290 without being directed into or in conjunction with the distribution nozzle or diffuser 1291. The gas from conduit 1290 may be introduced into the vessel or bioreactor 1202 at a designated location in a manner similar to a coarse bubble diffuser and serves as a source of oxygen or other gas to foster the microorganisms adhering to the adsorbent material and the microorganisms in the mixed liquor separated from the adsorbent material and as a source of lift to maintain the adsorbent material and biomass in suspension in the bioreactor 1202. Specifically, the draft tube 1292 provides upward lift due to the gas contained therein. When the bubbles rise inside the draft tube, they cause an upward flow, providing suction at the bottom of the tube. This is used to draw the mixed liquor and adsorbent material through the tubes and to raise the power of the suspension in the tank. Gas circulation provides sufficient elevation within the draft tube to maintain sufficient agitation of the cell contents such that deposition of adsorbent material becomes minimized or eliminated.

Furthermore, the configuration of fig. 12 provides for thorough mixing and suspension, while having significantly less energy requirements than other mixing and suspension systems. For example, the gas lift system 1232 in the bioreactor 1202 using adsorbent materials requires less than one tenth the energy required by other suspension systems, and may be as long as the gas required by the biological system.

Although gas lift suspension system 1232 is shown and described as being constructed with multiple flow conduits and located proximate to a gas source, other configurations may be employed, such as one or more tanks within a bioreactor, or other suitable configurations that produce the aforementioned gas lift phenomena. Furthermore, the directional keys shown in FIG. 12 are only illustrative of one possible way in which fluid may flow throughout the system, and may be any way through the system depending on system parameters, including the size and shape of the vessel, the size, shape and number of flow conduits, and the air flow rate.

Fig. 13A and 13B show additional embodiments of the present invention incorporating deposition section 1382 as part of a separation subsystem. In fig. 13A and 13B, solid black units represent adsorbent materials, and irregular linear units represent microorganisms or biomass. Bioreactor 1302 includes an inlet 1306 for receiving wastewater to be treated and an outlet 1308 fluidly coupled to a membrane operating system (not shown). A deposition section 1382, such as a stationary section, is located proximal to the outlet 1308 and is generally defined by baffles 1380 and 1381 positioned and sized to direct the adsorbable material away from the deposition section 1382. The combined mixture of liquid and adsorbent material flowing over baffles 1380 is deposited because of the substantially reduced turbulence caused by the jet aeration or other suspension system in bioreactor 1302 in deposition zone 1382. The adsorbent material, which has a higher density than the suspended biosolids, is deposited and returns to suspension as it exits the deposition section 1382 by turbulence caused by the suspension system located outside the deposition section 1382. As shown in fig. 13A, a screening device 1322 is also provided proximate the outlet 1308. The amount of adsorbent blocked by the screening device 1322 due to the adjacent deposition zone 1382 is minimized. In certain preferred embodiments, the screening device 1322 is located inside the baffle system, at a sufficient distance from the baffle to ensure that a majority of the adsorbent material will separate/settle from the mixed liquor before reaching the mesh screen. As a result, the screening device 1322 will receive fewer sorbent particles which may adhere to the screen surface and accelerate clogging/fouling of the screen. When the screening system is used in combination with the baffle system, the clogging/fouling of the mesh screen is greatly reduced, and the frequency of cleaning the mesh screen is also greatly reduced.

It is contemplated that in certain embodiments, the screening device 1322 may be eliminated altogether. The use of baffles around the aeration tank outlet 1308 reduces the mixing energy provided by the suspension device while leaving the settling section 1382 free of turbulence and elevated gas bubbles, so that denser sorbent particles can be separated from the mixed liquor by the effluent scrubber before the mixed liquor exits the tank. The baffle system allows the tight adsorbent material to separate from the mixed liquor while simultaneously directing the mixed liquor back to the mixing section of the aeration tank.

Other deposition zone systems internal to the bioreactor are also contemplated. For example, any of the mesh screens described above may be used, or a weir may be used in place of the screening device 1322 as described in more detail below.

The combination of the deposition zone and the shear action provided via pumping, mixing or jet aeration allows for the deposition of adsorbent material from which excess biomass has been sheared in the unmixed zone. Adsorbent material will be deposited at the bottom of this zone and re-enter the mixed liquor.

Fig. 13 shows another embodiment of a deposition section with a weir 1323. The low density biomass flows over weir 1323 and the adsorbent is deposited. As the adsorbent leaves the quiescent zone, its agitated contents of the mixing tank, including the mixed liquor suspended solids and adsorbent, are resuspended.

In embodiments of the invention, including a deposition zone having an adsorbent material waste discharge port, the waste discharge port is preferably located proximate the deposition zone. This allows the waste adsorbent material to be removed while reducing the removal of mixed liquor.

Adsorbent materials useful in the present invention include various types of carbon, such as activated carbon. In particular, granular activated carbon is extremely effective because the size range and density of the granules can be selected to allow them to remain in predetermined portions of the system, thereby preventing fouling and/or abrading of the membranes.

In systems where the granular activated carbon is not subjected to significant shear forces and/or inter-particle collisions, the granular activated carbon may be manufactured from wood, coconut, bagasse, sawdust, peat, pulp mill waste, or other cellulose-based materials. One suitable example is a MeadWestvaco Nuchar with a nominal mesh size of 14x35 (based on the U.S. Standard Sieve column)WV-B。

In additional embodiments, particularly where the shear force is provided by turbulence within the pump and/or jet nozzle and/or particle-to-particle collisions, it is desirable to use adsorbent materials having higher hardness values. For example, granular activated carbon derived from pitch or coal-based materials is effective. In a particular embodiment, the granular activated carbon is derived from lignite.

Carbon materials may also be provided which are modified and/or the species of which provide affinity for certain chemical classes and/or metals in wastewater. For example, in wastewater having a relatively high concentration of mercury, at least a portion of the adsorbent material preferably comprises granular activated carbon impregnated with potassium iodide or sulfur. Other treatment and/or impregnation species may be provided to target specific metals, other inorganic compounds, and/or organic compounds.

Further, the adsorbent may be a material other than activated carbon. For example, iron-based compounds or synthetic resins can be used as adsorbent materials, alone or in combination with other adsorbent materials, such as granular activated carbon. Still further, treated adsorbent materials other than activated carbon targeting certain metals, other inorganic compounds, and/or organic compounds may be used. For example, in wastewater containing relatively high concentrations of iron and/or manganese, at least a portion of the adsorbent may comprise a particulate manganese dioxide filter media. In the arsenic-containing wastewater, at least a portion of the sorbent can comprise a particulate iron oxide composite. In wastewater containing lead or heavy metals, at least a portion of the adsorbent may comprise a particulate aluminosilicate complex.

In one embodiment, the adsorbent material may be selected based on a desired specific gravity range. To maintain the adsorbent material in suspension within an acceptable energy expenditure/cost range, it is desirable that the specific gravity range be relatively close to the wastewater specific gravity. On the other hand, in embodiments where separation is at least partially based on material deposition, a higher specific gravity is suitable. Generally, the specific gravity in water at 20 ℃ is preferably greater than about 1.05. In certain embodiments, the specific gravity is greater than about 1.10 in water at 20 ℃. In certain embodiments, a suitable upper limit for specific gravity is about 2.65 in 20 ℃ water.

Thus, adsorbent materials are selected having a range of specific gravities that provide adequate suspension and thus adequate contact with wastewater and its contaminants. Further, in certain embodiments, the specific gravity range provides sufficient sedimentation characteristics for subsequent removal of the adsorbent material from the wastewater. In additional embodiments, the selection of the specific gravity of the adsorbent material is minimized based on the energy required to maintain the adsorbent material in suspension.

In addition, desirable adsorbent materials, such as granular activated carbon, have a hardness level that minimizes the formation of fines and other particulates due to inter-particle collisions and other process effects.

The separation subsystem is designed to maintain a size of adsorbent material that is thereby prevented from entering the membrane operating system optimized to reduce the amount of adsorbent material and fines entering the membrane operating system. Thus, the methods and systems of the present disclosure reduce abrasion and fouling caused by carbon particles or other particulate materials impacting the membrane, while still providing the operational advantages associated with the use of adsorbent materials, including activated carbon.

The appropriate particle size of the adsorbent material is selected to compensate for the screening/separation method selected and the particular wastewater being treated. In certain preferred embodiments, the effective lower particle size limit of the adsorbent material is selected such that it is easily separable from the mixed liquor stream entering the membrane operating system tank in which the membranes are located. Generally, the effective particle size of the adsorbent material has a lower limit of about 0.3 millimeters, where greater than about 99.5 weight percent adsorbent material is above the lower limit; preferably having a lower limit of about 0.3 mm to an upper limit of about 2.4 mm (corresponding to a screen size of 50 to 8 based on U.S. standard sieve series), where greater than 99.5 wt.% of the adsorbent material falls between the lower and upper limits; and in certain preferred embodiments from about 0.3 mm to about 1.4 mm (corresponding to screen No. 50 to screen No. 14 based on U.S. standard screen rows), where greater than 99.5 wt.% of the adsorbent material falls between a lower limit and an upper limit. Granular activated carbon having a minimum effective particle size of about 0.5 mm to about 0.6 mm has proven to be easily and efficiently screened from the mixed liquor using a suitable separation system, and such effective size is also effective in maintaining suspension in granular activated carbon having a suitable density.

Examples

The invention will now be illustrated by the following non-limiting examples.

Example 1

Test scale programmable logic control membrane bioreactor system (Petro)^TMMBR test unit from ross siemens water technologies, wi) has an aeration tank with an anoxic zone, a capacity of about 3,785 liters (l) (1,000 gallons (gal)), and a membrane operating system comparable to a commercially available membrane bioreactor system, modified to accommodate the addition of granular activated carbon as described in the present invention. The wedge wire screen is located at the pump inlet that transports the mixed liquor from the aeration tank to the membrane operating system.

The aqueous basic synthesis feed had the following organic/inorganic material concentrations: 48 grams per liter (48 ounces per cubic foot (oz/cf)) of sodium acetate; 16 grams/liter (16 ounces/cubic foot) of ethylene glycol; 29 grams/liter (29 ounces/cubic foot) of methanol; 1.9 grams/liter (1.0 ounce/cubic foot) ammonium hydroxide; and 0.89 grams/liter (0.89 ounces/cubic foot) phosphoric acid. Ammonium hydroxide and phosphoric acid are appropriate nutrient balance sources for bacteria inside the membrane bioreactor system.

A sample wastewater mixture is prepared having a high concentration of biologically refractory and/or biostatic organic compounds. Specifically, the sample wastewater mixture contains the following concentrations of biologically refractory and/or biostatic organic compounds: 90 mg/l (0.09 oz/cubic foot) EDTA; 30 mg/l (0.03 oz/cubic foot) di-n-butyl phthalate, 120 mg/l (0.12 oz/cubic foot) 2, 4-dinitrophenol, 21 mg/l (0.021 oz/cubic foot) 2, 4-dinitrotoluene and 75 mg/l methyl t-butyl ether. The mixture is fed to an anoxic tank.

The membrane bioreactor was first operated without granular activated carbon to obtain baseline values. After long-term biological acclimation such that the membrane bioreactor is fully acclimated, only about 92% of the bioremediation and/or biostatic organic Chemical Oxygen Demand (COD) compounds in the effluent are removed, thus allowing about 8% of these compounds (measured as COD) to enter the effluent, as determined before the addition of granular activated carbon.

To determine the efficacy of granular activated carbon, 3800 grams (134 ounces) of MeadWestvaco Nuchar with a nominal mesh size of 14x35 (based on the U.S. Standard Sieve series)WV B was added to the aeration tank and the blower supplying air to the aeration tank was adjusted to feed 2124 standard liters per minute (slm) (75scfm) to the aeration tank, supplying excess air to maintain the granular activated carbon in suspension. The amount of mixed liquor suspended solids in the granular activated carbon-based unit added to the aeration tank was about 5000 mg/l (5 oz/cubic foot) at 20%.

After MLVSS acclimation, the total membrane operating system effluent COD concentration is less than 4%, thus achieving greater than 96% removal of biologically refractory and/or biostatic organic compounds measured as COD. FIG. 14 is a graph showing the various stages of biological acclimation, bioremediation and/or biostatic compound concentrations (in mg/L), and residual effluent concentrations (as a percentage of the initial) of a membrane bioreactor system. Specifically, fig. 14 shows a comparison of effluent concentrations before addition of granular activated carbon (stage a), during the acclimation period (stage B), and after acclimation (stage B). There was a very significant initial reduction in effluent COD concentration once granular activated carbon was added to the system, not shown in figure 14 because the adsorption capacity of granular activated carbon was exhausted in less than one day. The system was then stabilized such that about 6.5% feed COD remained after treatment. This indicates that the carbon adsorption capacity is exhausted over a period of time, and the biomass on the granular activated carbon begins to act to digest the bio-inhibitory compounds measured as COD. After the bacteria become fully established on the granular activated carbon surface, the effect of the attached growth/fixed membrane system becomes significant as confirmed by evaluation using electron microscopy. The remaining COD concentration in the effluent is reduced to less than 4% of the feed COD concentration, providing a COD removal efficiency of greater than 96% for highly concentrated feeds of biologically refractory and/or biostatic organic compounds.

The method and system of the present invention are used to avoid fouling and erosion of the membrane by retaining the carbon outside of the membrane operating system tank. By using larger sized carbon particles, screening and/or separation of the carbon particles becomes possible. On the other hand, the small particle size of powdered activated carbon prevents efficient filtration from the mixed liquor.

Example 2

Laboratory particle suspension calibration tests were performed using a 2000 ml graduated cylinder with a rotameter connected to a source of compressed gas and a pipe from the outlet of the rotameter to a pipe to the bottom of the cylinder. 20 grams (0.7 ounces) of thoroughly dried granular activated carbon was placed in a measuring cylinder. Room temperature distilled water was also added to the cylinder to wet the particles. The cylinder contents were mixed with a spatula to suspend the entire contents and remove air bubbles.

Air was added to the tube in the cylinder at an increasing rate until the first solid was suspended, and the airflow was recorded. The gas flow was increased until about 50% solids were suspended (based on the amount of carbon remaining at the bottom of the graduated cylinder) and the gas flow was recorded. The air flow is increased again until all the granular activated carbon is suspended. The final air flow was recorded. The results are shown in Table 1.

The energy required to suspend particles increases as more particles are suspended. Based on these results, the air requirement for suspended granular activated carbon was calculated to be about 7,080 to about 8,500slm per 1,000 liters of reactor volume (about 250 to about 300scfm per 1,000 cubic feet of reactor volume). In comparison, the industry standard for suspending biosolids without granular activated carbon is about 850slm/1,000 liters of reactor volume (about 30scfm/1,000 cubic feet of reactor volume). The air required to measure suspended granular activated carbon and biosolids using a simple coarse bubble diffuser system is up to 10 times higher than the air required to suspend the biosolids alone and provide the required oxygen for biological decomposition.

Example 3

Granular activated carbon suspension test cells were prepared using a diameter of 1.83 meters (6 feet) and a water depth of 2.59 meters (8.5 feet). An eductor jet nozzle from siemens water technology, rossi, wisconsin, usa, was mounted on the outer wall of the tank at a distance of 43.5 cm (17.125 inches) from the tank floor. The nozzles are directed horizontally towards the center of the slot as shown in figure 15. The granular activated carbon Mead Westvaco NucharWVB 14X 35/wood in a concentration of 50 mg/l was introduced into the tank.

As shown in fig. 15, spray nozzle system includes spray nozzle 1544 that includes a fluid inlet 1546, a compressed gas inlet 1558, and an outlet 1564. Fluid enters mixing chamber 1566 from inlet 1546. The compressed air also enters the mixing chamber 1566 where it expands and provides energy to the fluid. As the air expands, the mixture of fluid and air is delivered to the nozzle throat 1568 where the velocity of the mixture increases. The air-containing fluid exits nozzle 1544 and enters the slots via outlet 1564.

The tests were performed using various liquid flow rates and compressed air flow rates. The liquid flow rate was in the range of 530 liters per minute (lpm) to 757lpm (140 gallons per minute (gpm) to 200gpm), while the compressed air flow rate was in the range of 0 to 850slm (30 scfm).

An air flow rate of 850slm (30scfm) resulted in suspension of the activated carbon, while air flow rates of 425slm (15scfm) and below resulted in deposition of the activated carbon on the bottom of the cell, at a liquid flow rate of 587lpm (155 gpm). Similarly, an air flow rate of 850slm (30scfm) resulted in suspension of the activated carbon, while air flow rates of 425slm (15scfm) and below resulted in deposition of the activated carbon on the bottom of the cell, at a liquid flow rate of 644lpm (170 gpm). Increasing the liquid flow rate to a liquid flow rate of 700lpm (185gpm) resulted in suspension of the activated carbon at a reduced air flow rate of 425slm (15 scfm).

Increasing the flow rate of liquid through the nozzle from 644 to 700lpm (170 to 185gpm) reduced the air consumption by 50% compared to the air required by a coarse bubble diffuser system. As such, the jet levitation system significantly reduces compressed air consumption, thereby reducing costs associated with the use of compressed air.

Example 4

Example 4 was conducted to measure the effect of the injection nozzle in performing suspension of the granular activated carbon and to verify the structure of the membrane that reduces the delivery of the granular activated carbon to the downstream membrane operating system. The cylindrical groove and the jet mixing nozzle are used for verifying that the granular activated carbon can be completely suspended by jet mixing. Various mixed liquid and gas flow rates were evaluated.

As shown in fig. 16, 18 and 19, the jet mixing/aeration nozzle 1644 is mounted on a 6 foot diameter 9,085 liter (2,400 gallon) steel tank 1602, filled with about 7,570 liters (about 2,000 gallons) of filtered tap water to a height L.

In this example, MeadWestvaco Nuchar, which is mainly woodWV-B granular activated carbon and Norit Darco mainly using coalThe MRX granular activated carbon was suspended at various liquid and gas flow rates by means of a jet mixing nozzle having a cylindrical groove. Mead NucharWV-B granular activated carbon has a specific gravity of 1.1, an effective size of 0.6 millimeters (0.024 inches), and is typically relatively softer than coal-based granular activated carbon; darcoThe MRX granular activated carbon had a specific gravity of 1.5, an effective size of 0.7 mm (0.028 inches).

About 50 mg/l (0.05 oz/cubic foot) of wood based granular activated carbon was added to the water. The low concentration of granular activated carbon is used to allow the use of a bottom video camera to view the mixing in the tank. Table 2 below shows the range of test conditions used.

Table 2: test conditions for granular activated carbon spray suspension

Condition	Liquid Rate, lpm (gpm)	Air velocity, slm (scfm)
			1	530(140)	0(0)
2	587(155)	425(15)
			3	644(170)	850(30)
4	700(185)	425(15)
			5	757(200)	0(0)
6	644(170)	425(15)
			7	700(185)	0(0)
8	700(185)	850(30)

9	644(170)	0(0)
			10	587(155)	850(30)
11	587(155)	0(0)

Water is fed to the nozzles of the jet mixing/aeration aerator 1644 by a disc pump 1648 and compressed air is injected from a blower 1660. Variable frequency drives 1649 and 1661 control pump and blower motor speeds, respectively, allowing adjustment of individual feed rates. A magnetic flow meter in the discharge line of the disc pump 1648 monitors the liquid flow. The blower motor speed is proportional to the air flow rate.

Referring to fig. 17, the throat velocity of the spray nozzle was calculated for each test condition and plotted against the liquid flow rate. As shown, a minimum throat velocity of about 10.4 meters per second (34 feet per second) is required to achieve complete suspension of the wood-based granular activated carbon. This rate can be related to the specific gravity and maximum particle size of the granular activated carbon.

At the completion of the test using wood-based granular activated carbon, the tank was drained, cleaned, and refilled with water, and approximately 50 mg/l of coal-based granular activated carbon was added. Based on a similar test column, it was observed that the jet aerator can maintain a more dense granular activated carbon in suspension.

Because of the need to substantially prevent granular activated carbon particles from reaching the membranes of the downstream membrane operating system, a slotted mesh screen with 0.38 mm openings was placed at the aerator/reactor tank outlet so that any granular activated carbon particles that broke down to less than 0.38 mm (0.015 inch) diameter particles during the jet aeration cycle would pass through the mesh screen, allowing them to enter the membrane operating system.

In addition, two tests were conducted using a stationary section, i.e., a low turbulence section, which allowed granular activated carbon to settle before reaching the mesh screen, which was placed on the suction side of the jet pump in the aeration/reactor tank.

In the first test and referring to fig. 18, a near stationary section is formed in the aeration tank 1802 using vertical baffles 1894. The baffle extends from 0.61 meters (2 feet) above the tank bottom to a height above the water surface. In this configuration, the screen 1822 is a wedge wire screen and is mounted near the top of the stationary section, which requires water to be drawn from the bottom of the tank 1802 through the low turbulence section before reaching the screen 1822. The size of the quiescent zone is 40-50% greater than the plug flow calculated by the unit, so the upward velocity is lower than the deposition rate of granular activated carbon. In order for this configuration to be effective, the deposition rate, which depends on the specific gravity of the particles, must be greater than the upward velocity. The test was conducted using a granular activated carbon based on coal, which calculated a deposition rate of 1.8 m/s. Given that the stationary section is a plug flow, it would take at least 0.39 square meters (4.2 square feet) to maintain an upward velocity low enough to allow granular activated carbon to deposit. The actual cross-sectional area of this section is 0.73 square meters (7.8 square feet).

Still referring to FIG. 18, the nozzle 1844 for feeding the pump's slot 1802 is positioned about 15.2 centimeters (6 inches) from the bottom of the slot. The polyvinyl chloride pipe is attached to the nozzle 1844 using a rubber shoe so that the wedge-shaped wire mesh screen 1822 can be suspended near the trough roof and in fluid communication with the outlet 1808. The wedge wire screen was 8.9 meters (3.5 feet) in diameter, 0.91 meters (3 feet) long, and had 0.38 millimeters (0.015 inch) openings.

The mixing test was run for about 18 hours on-stream using a 700lpm (185gpm) water flow rate and a 419slm (14.8scfm) air flow rate. The granular activated carbon was observed on the floor of the tank below the stationary section, while a small number of granular activated carbons remained suspended in the turbulent portion of the tank. Occasionally, swirling action will occur on the floor below the stationary section, and some of the granular activated carbon may be carried up towards the mesh screen.

When the pump and blower are turned off, part of the granular activated carbon existing on the mesh screen is separated in a fluff state, indicating that it is not strongly adhered to the mesh screen; the remaining granular activated carbon is easily removed using a light brush.

Referring to fig. 19, a second test was conducted using a trough 1902, a vertical baffle 1994, a nozzle 1944, and a mesh 1922 in fluid communication with the outlet 1902, the dimensions and placement being substantially the same as the equivalent assembly described with respect to fig. 18. In addition, second baffle 1993 is positioned below vertical baffle 1994 at an included angle of 45 degrees to dissipate the upward flow. The static section provides for reducing the amount of granular activated carbon reaching the mesh screen. Mechanical wipers or a back-flushing pulse of water or air may be used to loosen any granular activated carbon that may build up on the mesh screen over time.

Example 5

Example 5 was conducted to demonstrate the effectiveness of an air lift pump system using draft tube and trough mixing to effectively suspend the same wood-based and coal-based granular activated carbon materials used in example 4. Cylindrical and rectangular slots are used for each configuration. The granular activated carbon mainly composed of wood and the granular activated carbon mainly composed of coal of example 4 were used to measure abrasion; the mixing test used a higher density granular activated carbon based on coal.

The test data established that granular activated carbon can be suspended in the flow conduits and channels of both tanks using an air velocity comparable to that required to maintain biological respiration in both cylindrical and rectangular tanks. The data also show that at constant air flow rate, larger diameter draft tubes are more efficient than smaller draft tubes in terms of moving granular activated carbon from the surrounding region of the cell bottom to become suspended.

To determine the extent of attrition of the granular activated carbon, 0.31 meters (12 inches) diameter, 3.7 meters (12 feet) high section acrylic tube was charged with 150 liters (5.3 gallons) of water to 2.3 meters (92 inches), and 1,500 grams (53 ounces) of dry granular activated carbon was added to provide a concentration of about 1 weight percent. A polyvinyl chloride pipe having a diameter of 7 cm (3 inches) and a length of 2.1 m (82 inches) was fixed at the center of the 0.31 m (12 inches) diameter pipe to serve as a flow guide pipe. Four slots 2.54 cm (1 inch) high by 1.9 cm (0.75 inch) wide were placed at the bottom of the tube for the passage of granular activated carbon and water, and a 1.9 cm (0.75 inch) nozzle was placed at the center of the draft tube.

Air was introduced through the nozzle at 2,831 standard liters per hour (100 standard cubic feet per hour), corresponding to about 300slm per 1000 liters of water (300 scfm per 1000 cubic feet of water). This relatively high air flow rate is selected to produce more turbulent mixing than full scale operation to determine attrition. The fluids were allowed to mix for about 10 minutes before taking the first sample.

The measurement of abrasion during the test, from the acrylic tube top, snatch water sample and granular activated carbon sample, and pour the sample through No. 20 mesh screen. Solids from attrition were collected, dried and weighed through a mesh screen and estimated.

The results indicate that the granular active carbon wear rate is greater for granular active carbon based on wood (WV-B) than for granular active carbon based on coal (MRX). After 30 days of operation, about 10% wear rate of the wood-based granular activated carbon and about 5% wear rate of the coal-based granular activated carbon were observed. In the practice of the present invention, in a working bioreactor, this attrition rate can be replenished by solid waste during normal operation of the biological process. The test results are summarized in FIG. 20. Plotting also shows the y-intercept values and R for the standard linear regression analysis for each data set²The value is obtained.

Various configurations and variables of the ducts, such as the number of ducts, the distance of the ducts from the bottom of the tank, and the duct diameter, were tested and shown to perform.

In one configuration, referring to fig. 21 a single 0.3 meter (12 inch) diameter, 1.5 meter (5 foot) high draft tube 2192 is centered in a 1.8 meter (6 foot) diameter slot 2102 and above the bottom of the slot of foot 2195. Tank 2102 was filled with approximately 6,435 liters (1,700 gallons) of water to a water level L and sufficient coal-based granular activated carbon (400-. Air is supplied from a 2.54 cm (1 inch) diameter polyvinyl chloride coarse bubble diffuser tube 2190 which extends through the wall of the draft tube and has a number of 3.2 mm (0.125 inch) diameter holes drilled through its top surface. The air flow rate was varied from 141slm (5scfm) to 425slm (15scfm) and the slot bottom to draft tube spacing D was 8.3 cm (3.25 inches) or 1.9 cm (0.75 inches).

When used in connection with this test column, the term "impingement zone" refers to a zone of the tank surrounding the draft tube that is free of granular activated carbon.

The same is true when the draft tube position is observed to be 8.3 cm (3.25 inches) above the bottom of the vessel and the impingement zone is 1.9 cm (0.75 inches) above the bottom of the vessel above the draft tube position. The optimum distance between the bottom of the draft tube and the floor of the tank under prevailing conditions is determined by routine experimentation.

The increase in air addition by a factor of two does not increase the impingement zone size by a factor of two. At 425slm (15scfm), a gap of 8.3 cm (3.25 inches) between the base plate and the draft tube produced an impingement section diameter of about 71 cm (28 inches), i.e., 20 cm (8 inches) beyond the outer wall of the draft tube, which is the largest observed impingement section.

In an effort to use the same amount of air to swell the impact section size, the configuration shown in fig. 21 was modified by adding a bottom train or flange that increased the total diameter of the draft tube and train to 71 centimeters (28 inches) from the horizontal extension of the draft tube bottom. All other conditions were as described above. The air flow rate was varied from 141slm (5scfm) to 425slm (15 scfm).

It was observed that increasing the train bottom to the draft tube bottom indeed increased the impact section size. Comparing an impact section of 71 cm (28 inches) without a bottom train but with equal air flow rate, the aforementioned impact section increased to 112 cm (44 inches) with an air flow rate of 425slm (15scfm), i.e. 20 cm (8 inches) beyond the outer edge of the bottom train. The impact section increases in proportion to the size of the apron.

These draft tube configurations create a flow pattern, illustrated in figure 22, in which water and suspended granular activated carbon are drawn downward and inward toward the inlet 2296 of the draft tube 2290. The stagnation zone is also presented in fig. 22.

In one embodiment, a smaller diameter, shorter draft tube is placed inside a larger draft tube, 1.82 meters (6 feet) long, the inner draft tube is mounted about 7.6 centimeters (3 inches) from the bottom of the vessel, and the outer draft tube is positioned 22.9 centimeters (9 inches) higher than the inner draft tube. The polyvinyl chloride plate extended from the bottom of the draft tube within 15.3 centimeters (6 inches) to form a 71 centimeter (28 inch) diameter apron. A plastic panel was attached to the top edge of the apron train at a location of about 12.7 centimeters (5 inches) above the outer surface of the 15.3 centimeter (6 inch) diameter draft tube to form a sloped or beveled surface. The modified draft tube was centered in a 1.82 meter (6 foot) diameter cell; the air flow rate was varied from 141slm (5scfm) to 425slm (15 scfm).

Taking the middle tube produced an impact section of about 112 centimeters (44 inches), which is comparable to a single draft tube with a 71 centimeter (28 inch) flange bottom. In both configuration configurations, the impingement section is about 112 centimeters (44 inches).

The draft tube configuration of fig. 21 was modified by replacing a 0.31 meter (12 inch) diameter draft tube with a single 15.3 centimeter (6 inch) diameter draft tube. The air flow rate was again varied from 141slm (5scfm) to 425slm (15scfm), while the gap between the bottom of the slot and the draft tube was tested between 8.3 cm (3.25 inches) and 6.4 cm (2.5 inches).

These test results indicate that a change in spacing from 8.3 cm (3.25 inches) to 6.4 cm (2.5 inches) does not significantly change the impingement section diameter around the tube.

The air flow rate is increased by a factor of two without increasing the impingement section size by a factor of two. The maximum impingement section was produced with a condition of 425slm (15scfm) and a gap of 8.3 cm (3.25 inches) between the bottom plate and the draft tube, which configuration produced an impingement section diameter of about 56 cm (22 inches), i.e., 20 cm (8 inches) beyond the outer wall of the draft tube.

Based on the foregoing tests, it was concluded that for a given air flow rate, larger diameter draft tubes are more effective than smaller draft tubes for suspending granular activated carbon within the tested range and size. It is apparent that more than one draft tube may be required to suspend the granular activated carbon in a 1.82 meter (6 foot) diameter tank. While increasing the air flow rate does increase the mixing rate and magnitude of the impingement section to a point, doubling the air flow rate does not double the impingement section. The floor of the tank, with or without a bottom train or flange, having an area about 20 centimeters (8 inches) beyond the periphery of the draft tube, consistently removed granular activated carbon. Other configurations and/or supplemental mixing devices may be employed in the trough to push the granular activated carbon toward the draft tube impingement section.

In another configuration and referring to fig. 23, three evenly spaced 12-inch diameter draft tubes 2392 are placed within the trough 2302, fixed to each other such that the center of each draft tube is 0.61 meters (24 inches) from the center of the trough and is approximately 0.31 meters (12 inches) from the center of the draft tube to the wall of the trough. Each draft tube was suspended about 7 cm (3 inches) from the bottom of the tank.

Air was supplied uniformly to each draft tube through 1 inch diameter polyvinyl chloride tubes each provided with two 3.2 millimeter (0.125 inch) holes. The total air supply to all three draft tubes was 453slm (16 scfm).

To aid in the mixing and movement of the granular activated carbon forming just outside the impingement section of the three draft tubes, a water distribution system of 2.54 cm (1 inch) polyvinyl chloride tubes with pores was made to sit on the bottom of the tank. The holes were drilled approximately 32 cm (7 inches) apart on alternate sides of the tube so that the water was directed at a 45 degree angle to the bottom plate. Water was supplied to the distribution system from a separate water storage circulation tank at 53lpm (14gpm) by a centrifugal pump. This configuration resembles the return water from the membrane operating system in a membrane bioreactor system. A second pump and valve control the flow of water back to the storage tank, and a mesh screen is used to hold the granular activated carbon in the test slot.

It was observed that each draft tube cleared an area extending 20 cm (8 inches) beyond the outside wall of the draft tube, and that each hole of the water distributor system cleared an area (31-41 cm (12-16 inches) long and 20-31 cm (8-12 inches) wide). In the region between the impact section of the draft tube and the water distributor, some granular activated carbon deposits to the floor of the tank, but does migrate slowly to the impact section where it is lifted in suspension.

In yet another test of the water distribution system, the apertures of the water distributor tubes were oriented to cause the discharge water to mix the trough in a circular pattern.

All other conditions included water distributor tube spacing, air flow rate and water flow rate as described by three 31 cm (12 inch) diameter and 91 cm (36 inch) high draft tubes, with the membrane operating system tank returning water to be added evenly to the tank.

The test results indicated that each draft tube clearance zone extended 20 centimeters (8 inches) beyond the outer side wall of the draft tube. In addition, the water stream can effectively mix the granular activated carbon in a circular pattern. Granular activated carbon accumulation in the center of the tank can be eliminated by placing a draft tube in the center of the tank instead of three around the periphery.

It was observed that the granular activated carbon mixed to the top of the water level in the tank even when the length of the draft tube was shortened from 152 cm (60 inches) to 91 cm (36 inches). In addition, the use of a water distributor to add return liquid to the bottom of the tank effectively removes the surrounding granular activated carbon. When multiple draft tubes are positioned inside the tank, the size of the impact zone surrounding each draft tube is equal to the size of the impact zone observed surrounding a single draft tube, i.e., 20 cm (8 inches) beyond the outside wall of the draft tube.

In another configuration and referring to fig. 24, and for comparison of tank mix properties to circular tank mix characteristics, a rectangular tank 2402, 0.91 meters (3 feet) wide, 2.1 meters (7 feet) long, and 2.7 meters (9 feet) deep, filled with 2.4 meters (8 feet) of water, was provided. The blower, blower motor, and flow meter are set and operated as discussed previously.

As shown in fig. 24, the outside 31 cm (12 inches) of the tank floor 2405 is sloped at a 30 degree angle, which has previously been judged as the angle at which granular activated carbon begins to slide in an aqueous environment. The 30 degree angle of the inclined wall causes the granular activated carbon to be directed toward the draft tube inlet.

Two 31 cm (12 inch) diameter draft tubes 2492 each 91 cm (36 inches) in height and supported about 12.7 cm (5 inches) from the base of the trough are evenly spaced across the non-inclined portion of the trough 2402. A 7.6 cm (3 inch) diameter air tube 2490 with drilled openings is positioned below the draft tube to direct air into the draft tube through the three coarse bubble diffusers. The air flow rate was varied from 221slm (7.8scfm) to 512slm (18.1 scfm).

All air flow rates in this range for granular activated carbon were satisfactorily mixed. The higher the air flow rate, the more intense the mixing flow rate and the less time the granular activated carbon will remain on the bottom plate of the tank. During the air addition, the presence of granular activated carbon was observed throughout the depth of the trough.

In another configuration and referring now to fig. 25, a "draft trough" 2592 is formed by providing a trough 2502 with sloped walls and diffusers as previously described in connection with fig. 24, with the addition of two parallel baffles 2597, 61 cm (24 inches) in height, 31 cm (12 inches) apart and 6.4 cm (2.5 inches) above the floor of the trough. The air flow rate through tube 2590 was from 90.6slm (3.2scfm) to 331.3slm (11.7 scfm). It was observed that at all air flow rates above 141.6slm (5scfm), the granular activated carbon was thoroughly mixed and suspended, and increasing the air flow rate above 141.6slm (5scfm) increased the mixing rate.

In additional tests, in which the cell floor and diffuser configuration were the same as those described for figures 24 and 25, without draft or draft tubes, it was found that even for 1133slm (40scfm), less than 10% granular activated carbon suspension was visible visually, indicating the presence of cells as a very significant factor in the energy efficient suspension of granular activated carbon.

In another test configuration, the distance from the cell wall to the flow leader increases. In a large aeration tank, it is economically advantageous to separate the flow guide grooves by a large distance. Tests were conducted to determine the effect of extending the inter-cell spacing to 2.1 meters (7 feet). To determine this, the configuration described above and described with respect to fig. 25 was rotated 90 degrees within the slot. Two 30 degree angled ledges were provided extending 91 cm (36 inches) from each end of the trough.

The coarse bubble diffuser was made via nine 3.2 cm (0.125 inch) diameter holes evenly spaced along a 91 cm (36 inch) bore of 7.6 cm (3 inch) diameter polyvinyl chloride pipe. The air flow rate was varied from 164slm (5.8scfm) to 402slm (14.2 scfm).

The bubble diffuser is disposed in the center of the tank. Two parallel baffles, 91 cm (36 inches) long, 61 cm (24 inches) high, 31 cm (12 inches) apart and 6.4 cm (2.5 inches) above the floor of the tank, were used to form a channel between the two sloped walls.

The granular activated carbon was observed to be well mixed and suspended throughout the range of air flow rates. Granular activated carbon sweeps down the slope and into draft slots at intervals up to 2.1 meters (7 feet) with a 30 degree inclined floor between them.

As the foregoing tests indicate that a draft tube design, using an inclined floor or wall extending 30 degrees from the vertical side wall toward the draft tube, can successfully suspend granular activated carbon at 0.91 meters (3 feet) wide, 2.1 meters (7 feet) long, and 2.4 meters (8 feet) of water volume.

Additional tests were conducted using a 91 cm (36 inch) long baffle basin as described above, with different basin floor configurations to further optimize energy efficiency for suspending granular activated carbon. The configuration includes completely removing the slanted floor, tilting the floor from the outer sidewall to the draft trough, and reducing the angle from 30 degrees to 15 degrees, and reducing the slanted floor from a 91 cm (36 inch) length at each end of the trough to 31 cm (12 inches) at each end while maintaining the 30 degree angle. In addition, a test was conducted in which a slot bank was fitted with two 91 centimeter (36 inch) long channels at each end of the slot without an inclined floor. The respective air flow rates in these configurations varied from 141slm (5scfm) to 425slm (15 scfm).

Two flow guides are mounted at each end of the test aeration tank. The channels were formed by placing a 91 cm (36 inch) coarse bubble diffuser at each end of the channel. The diffuser was fabricated from 7.6 cm (3 inch) polyvinyl chloride pipe with 5 evenly spaced 3.2 cm (0.125 inch) holes. About 20 cm (8 inches) from the wall, i.e., 6 inches from the center of the diffuser, a baffle 91 cm (36 inches) long and 61 cm (24 inches) tall was installed, about 5.1 cm (2 inches) from the floor of the tank.

From tests performed in a rectangular test scale aeration tank, it was observed that three pilot tubes of 31 cm (12 inches) diameter and 91 cm (36 inches) height were added to the diffuser to suspend the granular activated carbon at air flow rates of 227slm (8scfm) to 510slm (18 scfm). However, this configuration may result in stagnant sections near the strut and slot corners. A guiding gutter 2.1 meters (7 feet) long was placed in the center of the tank with the floor inclined at a 30 degree angle, and an air velocity higher than 141slm (5scfm) produced thorough mixing and suspension of the granular activated carbon in the tank. Further testing indicated that sufficient mixing was achieved with channel spacing up to 2.1 meters (7 feet).

In the above-described configuration using the flow guide tube, it is obvious to increase the air flow rate to reduce the back flow. Increasing the air flow rate does increase the mixing rate and impingement zone size. But doubling the air flow rate does not double the impingement section size. The impingement section of each draft tube appeared to extend about 20 centimeters (8 inches) beyond the outer side edge of the tube. Beyond this zone, additional local mixing of the materials in the tank is required to remove the granular activated carbon from the floor of the tank towards and to the draft tube impingement section. This mixing is accomplished using a water distribution system.

Even when the length of the draft tube was shortened from 152 cm (60 inches) to 91 cm (36 inches), the granular activated carbon was suspended throughout the depth of the tank. The tank bottom plate is inclined at an angle of 30 degrees towards the flow guide pipe or the flow guide groove, and an effective method for circulating granular activated carbon is provided. The use of the flow-guiding channels and the inclined floor provides complete mixing of the granular activated carbon in the rectangular channels and is less sensitive to the formation of stagnant zones than the use of flow-guiding tubes. The diversion trench can effectively lift the granular activated carbon away from the trench bottom plate. Once the granular activated carbon is lifted above the draft trough, the mixing created by the coarse bubble diffuser is sufficient to lift the granular activated carbon to the top of the trough. The test results indicated that using a 30 degree incline allowed for 2.1 meter (7 feet) separation between channel centers, and greater separation was also possible.

Example 6

A wastewater treatment system designed substantially as illustrated in one or more of the foregoing embodiments and figures of the invention includes a first bioreactor, and a second bioreactor downstream of the first bioreactor comprising granular activated carbon. The membrane operating system tank is located downstream of the bioreactor. Operating parameters such as flow rate, residence time, temperature, pH, and the amount of granular activated carbon present in the system are adjusted to identify optimal performance conditions and to provide acceptable concentrations of biological oxygen demand and chemical oxygen demand compounds in the effluent leaving the system. Water flow between the first reactor and the second reactor is controlled to provide flow in a downstream direction and to maintain the granular activated carbon in the second reactor.

During operation, a wastewater stream is introduced into the first bioreactor. Phosphorus, nitrogen, and/or pH adjusting materials are added as needed to maintain the optimum nutrient ratio and pH of the first reactor. The microorganisms in the first reactor can decompose at least a portion of the biologically labile organics in the wastewater and reduce the biological oxygen demand compounds in the effluent to an acceptable level. The second bioreactor containing granular activated carbon is used to treat biologically refractory and/or biostatic compounds in wastewater and to reduce chemical oxygen demand compounds in the effluent to acceptable levels.

Using a suspension system, the granular activated carbon was maintained in suspension in the second reactor. A mesh screen was placed in the second reactor to maintain the membrane operating system substantially free of granulated activated carbon. Granular activated carbon is added to the second reactor as needed based on the measured biological oxygen demand compounds and chemical oxygen demand compounds in the effluent.

After passing through the mesh screen, the effluent from the second reactor is directed to the membrane operating system. In a membrane operating system, the treated wastewater will pass through one or more membranes. The membrane permeate will be discharged through the membrane operating system outlet. The retentate, including activated sludge, will be returned to the first reactor via a return activated sludge line.

Spent granular activated carbon from the second bioreactor is periodically removed through a mixed liquor waste discharge port. The waste outlet is also connected to a return activated sludge line to divert some or all of the return activated sludge to waste disposal, such as to control the concentration of components in the reactor.

The system includes a controller to monitor and adjust the system as desired. The controller indicates any parameter within the system based on the desired operating conditions and the desired quality of the effluent stream. The controller adjusts or regulates the valves, feeders or pumps associated with each potential flow based on one or more signals generated by sensors or timers located within the system, or based on the upward or downward trend of monitored system characteristics or properties over a predetermined period of time. The sensor generates a signal indicating that a concentration of a contaminant, such as biologically refractory/biologically inhibitory organic and inorganic compounds, has reached a predetermined value or trend, triggering the controller to initiate a predetermined action upstream, downstream, or corresponding to the sensor. This action includes any one or more of adding granular activated carbon to the bioreactor, adding different types of adsorbent materials, adjusting wastewater flow to a reactor inside the system, diverting wastewater flow to a tank inside the system, adjusting gas flow inside the bioreactor, adjusting residence time inside the bioreactor or other device, and adjusting temperature and/or pH inside the bioreactor or other device.

In order to achieve predetermined concentrations of biological oxygen demand and chemical oxygen demand compounds in the effluent, the first and second reactors are operated with their own water retention times. The water residence times of the first and second reactors are varied to determine the optimum ratio of the first reactor water residence time to the second reactor water residence time. The total water residence time of the system must be equal to or less than a standard single bioreactor, for example about 8 to 12 hours. In a preferred mode of operation, the first reactor has a water residence time of about 4 hours to about 8 hours, while the second reactor has a water residence time of about 4 hours. Generally, the water residence time of the first reactor will be longer than the water residence time of the second reactor; but the relative time will vary depending on the type of wastewater being treated. The water residence time and flow rate of the system were used to determine individual reactor sizes according to standard practice in the art. The effluent from the system must have at least about a 10% lower chemical oxygen demand compound than the effluent from a standard single bioreactor. Furthermore, in a preferred embodiment, the regeneration of granular activated carbon is accomplished through the use of such a system.

Example 7

A bench scale system was constructed and tested to simulate activated sludge treatment followed by activated sludge/granular activated carbon combination treatment. This test was performed to determine the effect of using granular activated carbon in a bioreactor (second stage reactor) downstream of the bioreactor (first stage reactor) which did not contain granular activated carbon.

The first stage reactor was a 4 liter (1.06 gallon) tank containing only activated sludge. A fine bubble air diffuser with an air flow rate of 370 cubic centimeters per minute (23 cubic inches per minute) was used. The second stage reactor was a 3 liter (0.79 gallon) tank containing activated sludge and granular activated carbon (argaca carbon from siemens water technologies). The concentration of granular activated carbon in the second stage reactor was 20 grams per liter (20 ounces per cubic foot). A draft tube comprising a 5.1 cm (2 inch) diameter PVC conduit was set in the second stage reactor with a diameter of 12.7 cm (5 inches) to maintain the granular activated carbon in suspension at an air flow rate of 368slm (13 scfm). The mixed liquor suspended solids concentration in the first stage reactor was about 3,470 mg/l (3.5 oz/cubic foot), while the concentration in the second stage reactor was about 16,300 mg/l (16.3 oz/cubic foot). The total water residence time of the system was about 14 hours, the water residence time of the first stage reactor was about 6 hours, and the water residence time of the second stage reactor was about 8 hours.

The system was operated for more than 30 days. The average feed concentration of soluble COD into the first stage reactor was 130 mg/l (0.13 oz/cubic foot), while the average concentration of soluble COD of the first stage reactor effluent was 70 mg/l (0.07 oz/cubic foot), and was fed to the second stage reactor. The average soluble COD concentration, as measured in the second stage reactor effluent, was 62 mg/l (0.062 oz/cubic foot). This reduced soluble COD by more than 10% by the second stage reactor demonstrates the utility of a system having a bioreactor containing granular activated carbon downstream of a first bioreactor which does not contain granular activated carbon for treating wastewater.

Other aspects of the invention described herein include a separation subsystem in the second stage reactor and the use of a membrane operating system downstream of the second stage reactor, which can be applied to the apparatus described in this example to achieve efficient treatment of wastewater.

The method and apparatus of the present invention has been described above and in the accompanying drawings; modifications thereof will be apparent to those skilled in the art and the scope of the invention is defined by the appended claims.

Claims (22)

1. A wastewater treatment system for providing a treated effluent, comprising:

a first aerobic biological reaction zone constructed and arranged to receive and treat wastewater;

a fresh or recycled source of porous adsorbent material;

a second aerobic biological reaction zone comprising:

a dispersed mass of porous adsorbent material having an adsorption capacity for adsorbing biologically refractory and biostatic compounds and an ability to adhere microorganisms to the adsorbent material, wherein the combined characteristics of the adsorbent material result in the biological regeneration of the adsorbent material, and

a separation subsystem constructed and arranged to prevent passage of adsorbent material and to maintain adsorbent material and effluent from the first aerobic biological reaction zone in the second aerobic biological reaction zone constructed and arranged to receive effluent from the first aerobic biological reaction zone;

a suspension system constructed and arranged to maintain the adsorbent material in suspension in the second aerobic biological reaction zone;

a waste discharge port constructed and arranged to remove a portion of the mass of adsorbent material from the second aerobic biological reaction zone in response to the concentration of one or more organic and/or inorganic compounds in the treated effluent;

a membrane operating system downstream of the second aerobic biological reaction zone constructed and arranged to receive treated wastewater from the second aerobic biological reaction zone, the membrane operating system being substantially free of adsorbent material from the second aerobic biological reaction zone;

discharging the membrane permeate as a treated effluent, and

the membrane operating system is in fluid communication with the first aerobic biological reaction zone to recycle a portion of the membrane retentate comprising activated sludge to the first aerobic biological reaction zone, and

the adsorbent material inlet is located at one or more locations upstream of the second aerobic biological reaction zone and is in direct communication with the second aerobic biological reaction zone.

2. The wastewater treatment system of claim 1, wherein the first aerobic biological reaction zone and the second aerobic biological reaction zone are separate portions of the same vessel.

3. The wastewater treatment system of claim 1, wherein the first aerobic biological reaction zone and the second aerobic biological reaction zone are located in separate vessels.

4. The wastewater treatment system of claim 1, wherein the separation subsystem includes a mesh screen positioned at the outlet of the second aerobic biological reaction zone.

5. The wastewater treatment system of claim 1, wherein the separation subsystem includes a settling section located proximate an outlet of the second aerobic biological reaction section.

6. The wastewater treatment system of claim 5, wherein the settling section includes a first baffle and a second baffle positioned and sized to define a quiescent section in which the adsorbent material is separated from mixed liquor and settled within the mixed liquor at the bottom of the second aerobic biological reaction section.

7. The wastewater treatment system of claim 5, wherein the separation subsystem includes a mesh screen positioned proximate the outlet of the second aerobic biological reaction zone.

8. The wastewater treatment system of claim 5, wherein the separation subsystem includes a weir located proximate the outlet of the second aerobic biological reaction zone.

9. The wastewater treatment system of claim 1, wherein the first and second aerobic biological reaction zones are constructed and arranged to support biological oxidation.

10. The wastewater treatment system of claim 1, further comprising an anoxic zone upstream of the first aerobic biological reaction zone.

11. The wastewater treatment system of claim 1, wherein the suspension system comprises an air-lift suspension system.

12. The wastewater treatment system of claim 11, wherein the gas lift suspension system comprises at least one draft tube positioned within the second aerobic biological reaction zone and a gas conduit having one or more apertures constructed and arranged to direct gas to an inlet end of the draft tube.

13. The wastewater treatment system of claim 11, wherein the gas lift suspension system comprises at least one draft trough located within the second aerobic biological reaction zone, and a gas conduit having one or more apertures constructed and arranged to direct gas to a bottom of the draft trough.

14. The wastewater treatment system of claim 13, wherein the flow leader is formed by at least two baffles positioned within the second aerobic biological reaction zone.

15. The wastewater treatment system of claim 1, wherein the suspension system comprises a jet suspension system.

16. The wastewater treatment system of claim 1, further comprising

A sensor constructed and arranged to determine the concentration of one or more predetermined compounds; and

a controller in electronic communication with the sensor and programmed to direct performance of an action based on the measured concentration of the one or more predetermined compounds.

17. The wastewater treatment system of claim 16, wherein the action comprises removing at least a portion of the adsorbent material from the second aerobic biological reaction zone.

18. The wastewater treatment system of claim 16, wherein the act comprises adding adsorbent material to the second aerobic biological reaction zone.

19. A wastewater treatment system comprising:

a first aerobic biological reaction zone having a wastewater inlet and a first zone mixed liquor outlet,

a fresh or recycled source of porous adsorbent material;

a second aerobic biological reaction zone having:

a dispersed mass of porous adsorbent material having an adsorption capacity for adsorbing biologically refractory compounds and biologically inhibitory compounds, and an ability for microorganisms to adhere to the adsorbent material, wherein the combined characteristics of the adsorbent material allow for the biological regeneration of the adsorbent material,

a mixed liquor inlet in fluid communication with said first zone mixed liquor outlet,

a suspension system for the adsorbent material, wherein the suspension system,

a second zone mixed liquor outlet, and

a separation subsystem associated with the second zone mixed liquor outlet, the separation subsystem constructed and arranged to prevent passage of adsorbent material; and

a membrane operating system located downstream of said second aerobic biological reaction zone having:

an inlet in fluid communication with said second zone mixed liquor outlet, an

A treated effluent outlet.

20. The wastewater treatment system of claim 19, wherein the first aerobic biological reaction zone and the second aerobic biological reaction zone are separate zones of the same vessel.

21. The wastewater treatment system of claim 19, wherein the first aerobic biological reaction zone and the second aerobic biological reaction zone are located in separate vessels.

22. A method for treating wastewater to provide a treated effluent, comprising:

introducing the mixed liquor into a first aerobic biological reaction zone to form a treated mixed liquor;

passing the treated mixed liquor to a second aerobic biological reaction zone comprising a dispersed mass of porous adsorbent material having an adsorption capacity for adsorbing biologically refractory and biologically inhibitory compounds and an ability to adhere microorganisms to the adsorbent material, wherein the adsorbent material has a combination of characteristics that result in biological regeneration of the adsorbent material;

suspending the adsorbent material in the treated mixed liquor of the second aerobic biological reaction zone under conditions promoting adsorption of the bioresistant and biostatic compounds in the treated mixed liquor onto the adsorbent material;

passing effluent from said second aerobic biological reaction zone to a membrane operating system while maintaining adsorbent material in said second aerobic biological reaction zone,

discharging membrane permeate from the membrane operating system as treated wastewater; and

a portion of the membrane retentate is returned as activated sludge to the first aerobic biological reaction zone.