FI90856C - Method for treating waste water or similar impure water and precipitation aid used in the method - Google Patents

Description

90856

Method for kfisitating effluent or similar impure water and precipitation aid used in the method

The present invention relates to a method for treating effluent or similar impure water according to the preamble of claim 1.

According to this method, a component that causes the precipitation of organic matter is added to the water to be treated in the mixing zone, the mixture obtained from the mixture is passed to a separation zone where the precipitating substance is separated from the liquid, and the treated liquid effluent is removed from the separation zone.

The method according to the invention is particularly suitable for the treatment of wastewater from the pulp and paper industry, but it can also be used for the treatment of other industrial wastewater, such as wastewater from oil refining and plastics production, as well as municipal wastewater.

The invention relates to a precipitation aid for the treatment of effluent or similar impure water.

In the removal of organic matter from pulp and paper industry effluents, 0.4 to 0.6 kg of bio-sludge is formed for each removed BOD7 kg (BOD = Biological oxygen demand). T3ma organic matter contains living and dead microbes. In addition, it contains finely divided organic and inorganic solids that have been transported to the biological treatment plant together with the treated wastewater. Biomass accounts for 50-80% of the activated sludge in the pulp and paper industry.

In Finland, large amounts of Maaria activated sludge are already formed, · the amount of sludge is in the order of 30,000 to 40,000 tonnes of dry matter per year. MMar3 is still expected to grow to the order of 80,000 to 100,000 t / a at the end of the decade.

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There is no economically attractive benefit to bio-sludge. In its present state, it is either dried and incinerated together with the fibrous slurry or transported to the 13th zone. So far, the microbial part of Myfiska's activated sludge has hardly been utilized in wastewater treatment. In ErMissM cases, bound phosphorus and nitrogen have been released, which can be reused in biological purification.

The present invention stems from the idea that the activated sludge could be used as a precipitation aid in the pre-clarification of wastewater treatment. At this point, the activated sludge is often removed from the process together with the pre-clarification slurry by passing the bio-slurry with the incoming water to the pre-clarification. However, some of the bio-sludge may rise to the surface due to anaerobic effluent or other causes. The result is most often that the solids removal efficiency of the myCs pre-clarification deteriorates from the original.

Measurements and experiments performed in connection with our invention have now shown that by decomposing at least a part of the microbial cells in the sludge and setting the pH of the sludge to a maximum of 3, preferably in the pH range 2-3, additional biolludge for pre-clarification is obtained.

More specifically, the method for treating wastewater according to the invention is mainly characterized by what is set forth in the characterizing part of claim 1.

As stated above, in the context of this application, the term "bio-sludge" means a proteinaceous sludge from a sewage treatment plant, such as an activated sludge plant or an aerated pond, which contains non-destructive and dead microbes.

The terms "precipitate" and "precipitate" in turn refer to a process in which a substance in the solution phase changes

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3 90856 to a solid form, whereby it differs from the solution. The solid formed during precipitation may coagulate to form flakes or flocs which, depending on the process conditions, either settle to the bottom or - in the case of flotation or foaming - rise to the surface. Thus, the term "precipitation" encompasses those processes in which flake and floc formation and coagulation occur.

In the process according to the invention, a suitable acid, in particular a mineral acid, such as hydrochloric, nitric or sulfuric acid, may be used. However, it is also possible to use an acidic effluent fraction, such as ferrous sulphate-containing effluent from the chemical industry. Because the pH of the females is often quite low, even <1, they are particularly well suited to bring the pH of the alkaline stage effluents of pulp bleaching to the desired value.

According to the invention, the pH should be below about 3 for the slurry to precipitate. As can be seen from the examples of myohenun, the method does not give the desired result at a pH of about 4. For economic reasons, it is rarely sensible to lower the pH to less than two, although the method still works at female pH values.

The bio-slurry is added to the effluent in a mixing zone, where the effluent is mixed, e.g. in successive mixing tanks. In a preferred embodiment of the invention, the mixture of slurry and water is mixed in two steps, first rapidly and slowly. The steps are performed in different mixing vessels.

the consistency of the bio-sludge added to the effluent is about 0.2%, but it can be increased to about 2-3% by compacting the soil. At least a portion of its microbial cells, preferably at least about 50%, particularly preferably at least about 60%, are crushed by a suitable crushing treatment. According to a preferred embodiment, the bio-sludge is separated into a hand-held sonicator device ultra-ael. According to another preferred embodiment, the microbial cells of the bio-slurry 4 are crushed under high pressure and rapid reduction (rSj Ignition technique).

The maarS of the precipitating chemical required to effect precipitation varies depending on the dissolved and suspended compounds. Usually the dry matter content of the bio-slurry to be added is about 0.2 to 1.5 g / l of extension water.

In addition to the bio-slurry, precipitation chemicals known per se, such as ferro- and ferric sulphate and aluminum sulphate, can be used in the pre-clarification, which can be added, for example, in the form of an aqueous solution containing ferro-, ferric- or aluminum ions, such as the chemical ferrous effluent.

In addition to the bio-slurry and possible precipitating chemicals, a flocculation enhancing chemical known per se can be used in the process, in which various cationic polymers, anionic polymers and polyelectrolytes can be used depending on the composition of the effluent. The flocculation enhancer chemical is introduced into the effluent prior to, at, or simultaneously with the addition of the bio-sludge.

In order to separate the precipitated substance and the solution, the effluent-slurry mixture is led, for example, to the equalization tank or aeration section of the activated sludge plant, where the precipitated substance is separated by methods known per se.

The invention provides considerable advantages. Thus, a fairly good solids reduction of the effluent is obtained. If there is a fine, otherwise non-settling solid in the effluent, it precipitates at the same time. The method is suitable for the treatment of wastewater from both mechanical and chemical pulp production. Examples include peeling and bleaching waters. As some organic, high-molecular-weight substances, such as acids and chlorinated compounds, precipitate in the process, jStevesi from oil refining and plastics can also be treated. The invention allows the use of conventional precipitating chemicals

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5 90856 significantly reduced, they can even be completely replaced by the bio-slurry according to the invention.

In the following, the invention will be examined in more detail with the aid of the accompanying drawing and a few embodiments. The figure of the drawing shows a simplified process diagram of the method.

The process according to the invention uses a bio-slurry consisting of the supernatant sludge from the activated sludge process, which is crushed in the crushing device 1, as a pre-clarification precipitating aid. Crushed bio-sludge is added to the treated effluent in the first mixing vessel 2. The sludge is inoculated into the treated effluent so that its amount, measured as dry matter (evaporation fraction), is 0.2 to 1.5 g / l in the clarifying water. the pH of the effluent is obtained by adding an acidic effluent fraction or a mineral acid (sulfuric acid or the like) so that it is in the range of 2-3. The pH in the first mixing vessel is measured and obtained with an apparatus 3 consisting of a pH display, recording and accompanying device (QIRC) and an injectable acid substance flow, recording and accompanying device (FIRC).

The treated effluent is initially mixed rapidly for 1-2 minutes in the first mixing vessel 2 and then slowly for 6-10 minutes in the second mixing vessel 4. Coagulation of the slurry takes place in the tailings and the sludge and dissolved organic matter in the effluent begin to precipitate.

The sludge mixture is injected into a clarifier or flotation apparatus 6. If the sludge and water separation plant contains concrete or other parts susceptible to acid-induced corrosion, the pH of the mixture must be raised to 4.0 to 5.3, for example with lime (aqueous calcium hydroxide solution). 5. Adjust the pH of the mixture entering the clarifier as described above with the condenser 3.

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For clarification, a separator 6 (surface load 0.6 to 1.2 m3 / m2 h, residence time 3-5 hours) is conventionally required for the clarification of wastewater from the sailing and paper industry.

When flotation is carried out, the surface load can be of the order of 3-5 m3 / m2 h and the so-called in the amount of dispersion water 10 - 20% in the amount of treated water.

From clarification 6, the wastewater goes to a biological treatment stage. The sludge is directed to sludge treatment and treated with other wastewater treatment sludges by conventional methods.

The following examples illustrate the invention without limiting it in any way to the details of the examples.

Example 1 The wastewater to be treated was the effluent from the chemitermomechanical (CTMP) plant for pre-clarification during the spruce run. The bio-sludge used in the experiment was bio-sludge from an activated sludge plant of the same plant.

The bio-slurry was sonicated (sonicated) and the remaining solid was removed by centrifugation. The filtrate from the centrifugation was added in a constant amount to the effluent to be treated. pH

was adjusted with dilute sulfuric acid in different samples to different sizes. After the addition of acid, the samples were mixed at a constant rate for about 10 minutes and allowed to settle for about 30 minutes. The water portion was then sampled and the solid was determined using a GF / A filter. The results are shown in Table 1 below.

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Table 1 Effect of pH change on solids removal when crushed activated sludge is used as a precipitation aid.

Added pH solid solid active substance reduction in sludge volume 1) mg / 1% ml / l Untreated water 0 5.8 1700 1A comparison 0 2.0 540 68 IB test 50 2.0 140 92 1C test 100 2.0 82 95 2A test 0 4.0 570 66 2B test 50 4.1 650 62 2C test 100 4.0 740 56

The solids reduction has been calculated by comparing it to the solids content of the original water.

Example 2

By the sulfate method, the softwood pulp cooked in the hopper 31 was bleached on a laboratory scale using the sequence C / D E1DE2D. The aim was a brightness of ISO 90. The effluent from the alkali stage (from stage E1), the acidic effluent (from stage C / D) with C = chlorine and D = chlorine dioxide) and the filtrate of the sonication crushed and filtered by sludge were mixed together. Said sludge filtrate was mixed simultaneously with acidic wastewater with alkaline wastewater. The mixture was stirred for 5 minutes, after which the mixture was allowed to settle for about one hour. A sample of water was taken and the color was determined at a constant pH. The results are shown in Table 2 below. The mååråti volume ratios were alkaline water: acidic water: bio-slurry = 1: 2: 0.2 8

Table 2 Color reduction when adding crushed bio-sludge to a mixture of alkaline and acidic wastewater.

Color variation Reduction mg Pt / 1%

Acid effluent 320

Alkaline wastewater 6600

Biosludge 1500 Treated wastewater 690 71

In our other purification experiments, it has been found, among other things, that the addition of crushed biosludge to pre-clarification does not increase the amount of dissolved organic matter removed from the pre-clarification as measured by COD. The purification result in the precipitation of solids did not substantially deteriorate, although the uncrushed part of the sludge was not removed from the crushed biosludge by centrifugation.

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Claims (12)

90856 A method for treating wastewater or similar impure water, which method comprises - adding an organic precipitating component in water to the mixing zone (2, 4), from the separation zone and subjected to possible further processing, characterized in that - at least a partially proteinaceous bio-slurry is used as the precipitating component, the microbial cells contained in which have been subjected to a crushing treatment to a pH of about 3), and - a mixing zone (about 3). Process according to Claim 1, characterized in that bio-sludge from an activated sludge plant or an aerated pond is used, the at least about 50%, preferably about 60 to 90%, of the microbial cells being crushed. Process according to Claim 1 or 2, characterized in that the pH is adjusted to about 2 to 3. Process according to one of Claims 1 to 3, characterized in that an acidic effluent fraction or a mineral acid is used to adjust the pH. Process according to one of the preceding claims, characterized in that about 0.2 to 1.5 g of bio-sludge / l of water, calculated as dry matter, are added in the mixing zone (2, 4). Process according to one of the preceding claims, characterized in that the mixture of slurry and water is mixed in two stages, first rapidly and then slowly. 7. A precipitation aid, in particular for the treatment of waste water or similar impure water, for use at pH values of up to about 3, characterized in that it consists essentially of a proteinaceous bio-slurry which has been treated in such a way that at least some of the bio-sludge microbial cells are crushed. Precipitation aid according to Claim 7, characterized in that at least about 50%, preferably at least 60% of the microbial cells in the sludge are crushed. Precipitation aid according to Claim 7 or 8, characterized in that the bio-sludge is obtained from an activated sludge plant or an aerated pond. Precipitation aid according to one of Claims 7 to 9, characterized in that the consistency of the bio-sludge is about 0.2 to 3%. Precipitation aid according to one of Claims 7 to 10, characterized in that the bio-slurry is treated with ultrasound to disrupt microbial cells. Precipitation aid according to one of Claims 7 to 10, characterized in that the microbial cells of the bio-slurry are crushed by first subjecting the bio-slurry to a high pressure, which is then rapidly reduced. Il 90856