WO1997013727A1

WO1997013727A1 - Method and device for biologically treating liquids in the presence of particles forming a floating bed

Info

Publication number: WO1997013727A1
Application number: PCT/FR1996/001563
Authority: WO
Inventors: Jacques Manem; Valentina Lazarova
Original assignee: Lyonnaise Des Eaux
Priority date: 1995-10-13
Filing date: 1996-10-08
Publication date: 1997-04-17
Also published as: FR2739849A1; FR2739849B1

Abstract

A method for biologically treating liquids in a reactor containing a liquid to be treated and microorganism carrier particles having a lower density than the liquid to be treated and forming a floating bed in the liquid. According to the treatment method, a stationary floating bed is formed in a reactor having at least two sections separated by vertical walls and communicating via free spaces above and below the walls. The particle bed is scrubbed by injecting a gas into the lower portion of at least one of said sections to cause cocurrent circulation of the solid, gas and liquid phases through the reactor, in the form of an upflow in the air injection area and a downflow in the other area(s). A device for carrying out the method is also provided.

Description

"Method and device for biological treatment of liquids in the presence of particles constituting a floating bed".

The invention relates to a method of biological treatment of a liquid, and in particular a method of biological treatment of waste water, as well as a biological treatment device using such a method.

Wastewater treatment treatments use a biological reaction between the materials contained or suspended in the wastewater and an active biomass. This biomass can be free but it has been found that the fixing of microorganisms (constituting the biomass) on mineral or organic supports allows the maintenance of high concentrations of biomass in biological reactors, also called biαreactors. This ensures higher volume loads and more compact reactors than in conventional methods using free biomass. In the prior art of biological treatments using fixed cultures, there are essentially three groups of reactors: di- or three-phase fluidized bed reactors, turbulent bed reactors and fixed bed reactors. The latter are particularly advantageous from the point of view of their generally simple and inexpensive implementation. Examples of fixed bed reactors are aerated submerged biofilters with granular filling. Some use granular materials having a density higher than that of water ⁽ sand) while others use floating supports (Cf. DE-A-25 49 415, GB-A-2 239 192, FR- A-2 493 589, FR-A-2 669 917, FR-A-2 670 682, FR-A-2 673 932). However, a drawback of this type of bioreactor is the presence of a considerable part of inactive biomass due to the rapid clogging of the bed and the diffusion limitations. It is therefore essential to carry out frequent washing of the fixed bed, washing c which interrupt the treatment and produce large quantities of washing water to be recycled or treated specifically.

It would therefore be interesting to have a biological treatment process which does not have these

^ 0 disadvantages and which nevertheless allows an efficient treatment of waste water.

This is obtained according to the present invention which provides a method for biological treatment of liquid in a reactor containing liquid to be treated and

^ g support particles of microorganisms, of density lower than that of the liquid to be treated, forming a floating bed in the liquid bed, process in which, for the treatment, a fixed floating bed is established in a reactor with at least two zones separated by walls

Vertical _PQ leaving free passages above and below said walls and in which, for washing the particle bed, a gas is blown into the lower part of at least one of said zones to create a circulation in the reactor current of solid, gas and liquid oc phases in upward flow in the blown zone and in downward flow in the other zone (s).

According to a particularly advantageous variant, the biological treatment is carried out in downward flow,

30 with distribution of the liquid to be treated at the upper part of the floating bed, the latter advantageously consisting of particles of non-homogeneous particle size. Therefore, the larger particles are found in the upper part

35 of the bed and form a protective layer which retains the any suspended matter by reducing the risk of clogging the bed.

The washing of the bed is carried out by blowing a gas, which can be air, oxygen-depleted air or any other gas, for example a recovery gas. When the liquid to be treated is constituted by waste water, the gas is advantageously adapted to the type of treatment in progress, aerobic, anoxic or anaerobic. The gas blowing causes a co-current circulation of the three phases present, around the vertical walls, by the passages left free between them and the top and bottom of the reactor,

Washing the bed with gas has several advantages. It is simple to implement and is very short-lived, for example by injecting gas for less than five minutes. When the aeration stops, the floating particles settle up and the excess sludge settles, with self-separation of the phases. Therefore, the operation of the reactor can be done continuously without the need to stop the supply of liquid to be treated and the collection of the treated liquid. In addition, there is no need for a washing liquid circuit, neither to supply it nor to collect it. It is also not necessary to provide any installation for treating the washing liquid.

Apart from the advantage of the self-selection of the particle size of the support, the implementation of the fixed floating bed in descending flow has a particular advantage when the biological treatment comprises the three conventional stages of treatment of carbon pollution, nitrification and denitrification. Indeed, the course of the downward-flowing bed causes trapping of the gas bubbles <nitrogen) produced during the denitrilication stage, which results in a significant expansion, generally greater than 20%, of the floating bed. This expansion of a three-phase floating fixed bed improves the transfer between the solid matter and the liquid and further delays the clogging of the bed.

As support particles for microorganisms, use is preferably made of a granular plastic material, not absorbing water, and of any shape, preferably irregular in order to avoid any homogeneous distribution which facilitates clogging or the formation of preferential paths. . In general, a material having a lower density of 0.15 ± will be used. 0.10 g / cm ³ to that of the liquid to be treated. In the case of waste water, the actual density will generally be between 0.85 and 0.90 g / cm ³ with a particle size between 0.5 and 10 mm with, as indicated above, a wide particle size distribution. It will also be noted that the presence of a solid phase of low density such as that mentioned above, considerably reduces the energy requirements for washing the bed, by requiring low gas flow rates, much lower than those used in the processes with non-floating supports, and this in the presence of high filling rates which can in this case range from 30 to 80% volume / volume and preferably from 50 to 60% volume / volume, which makes it possible to significantly increase the amount of active biomass in the reactor. This gives maximum activity of the biomass fixed on the support particles and higher yields of the reactor are then obtained.

Such a treatment method is also particularly advantageous from an economic point of view, since the treatment itself is carried out without any energy input and that the blowing of air for the washing only results in relatively low energy expenditure.

The invention further provides a device for carrying out the method, consisting of a reactor comprising at least two zones separated by vertical walls leaving free passages above and below said walls and comprising in one of said zones a device for gas blowing.

In a preferred variant of the invention, the device is equipped with a device for distributing the liquid to be treated at the top of the reactor so that the treatment of the liquid takes place in a downward flow according to the preferred embodiment of the previous process. The method has a particular application for the treatment of particulate pollution (presence of suspended matter) and / or dissolved of a liquid, and in particular of waste water.

Other characteristics and advantages according to the present invention will appear on reading the following description, given by way of illustration with reference to the appended drawings in which FIG. 1 is a diagram of a device implementing the biological treatment phase according to the FIG. 2 is a diagram of a device implementing the washing phase according to the present invention, and FIG. 3 is a diagram of a device using ^e π in addition to a stirring device.

A reactor 1, for example but not necessarily of circular section, is separated into at least two zones by one or more vertical walls. In the example shown in FIGS. 1 and 2, the reactor is separated into three zones 3, 4 and 5 by two vertical walls 2. The floating particles are distributed homogeneously in the three zones 3, 4 and 5 by forming a floating bed. Contrary to what happens for fixed beds requiring a floor to hold the bed in the lower part for dense materials or upper for floating materials, this floating bed remains submerged by the combined action of the forces of gravity and Archimedes, without any device for holding the bed, both above and below. This also constitutes an important simplification of the device for implementing the method according to the invention.

When, as shown, the particle size of the particles 8 is variable, the particles of larger dimensions 8a remain in the upper part of the bed while the fines 8b are maintained at the bottom of the bed, with the consequence that the particles 8a have a first action filtration on suspended matter introduced with the liquid to be treated. The water to be treated 9 is distributed by a distribution system 10 located above the floating bed of particles 8. For this purpose, various distribution devices can be used, and we will cite by way of example only perforated ramps or with parallel or concentric weirs. The liquid is treated during the downward flow of the liquid down the bed, according to the arrows A.

The treated water is discharged through line 11, preferably through a phase separation device 12, comprising at least two rows of obstacles arranged in staggered rows, the use of which is particularly advantageous when washing the floating bed.

For the washing cycle, which takes place without the introduction of washing water, the reactor 1 is equipped with a gas injection device 7 located, for example, in zone 4. The injection of a washing gas 13, for example air, induces a homogeneous co-current circulation of the solid phase 8, of the liquid phase and of the gas bubbles 14 according to the arrows B (Figure 2). During this circulation, the granular material 8 is freed from suspended matter and / or excess biomass. The washing sludge is discharged at 15, preferably by means of a settling zone 6, located below the phase separation device 12 which, as described in French patent application N '95 04833, facilitates the separation between on the one hand the solid phase and on the other hand the liquid and gaseous phases. At the end of the insufflation, the particles 8 reform the floating bed as illustrated in FIG. 1, while the rest of the excess sludge continues to settle in zone 6.

FIG. 3 represents a variant of the reactor of FIG. 1, in which a stirring device 15 is provided, for example in the central zone 4, turning for example in the direction of the arrows C. This device 15 can, as shown in the figure, be located below the gas injection device 7, but it is also possible to envisage placing it above this device. This stirring improves the washing efficiency and in addition the use of such a stirring device makes it possible to give the floating bed, during the downflow treatment period, a certain stirring which further limits the risks of clogging of the bed. and the development of an excess of biomass on the particles, which further facilitates and minimizes the washing by gas injection and its frequency.

Claims

1.- Method for the biological treatment of liquids in a reactor containing the liquid to be treated and carrier particles of microorganisms, of density less than that of the liquid to be treated, forming a floating bed in the liquid, characterized in that, for the treatment , a fixed floating bed is established in a reactor with at least two zones separated by vertical walls leaving free passages above and below said walls and in that, for washing the bed of particles, a gas is blown into the lower part of at least one of said zones to create in the reactor a co-current circulation of the solid, gas and liquid phases in ascending flow in the blown zone and in descending flow in the other or the other zones.

2.- Method according to claim 1, characterized in that the particle size of the particles is non-homogeneous and the water to be treated runs through the floating bed in descending flow.

3.- Method according to either of Claims 1 and 2, characterized in that, during the operating and / or washing phase, the liquid, solid and gaseous phases are agitated using a agitator located in at least one of said zones.

4.- Method according to any one of claims 1 to 3, characterized in that one uses as carrier particles of microorganisms a granular material whose density is lower than 0.15 + _ 0.10 g / cm ³ to that of the liquid to be treated. 5.- Method according to any one of claims 1 to 4, characterized in that a material having a particle size of 0 is used as support particles for microorganisms,

5 to 10 mm.

6, - Method according to any one of claims 1 to 5, characterized in that the filling rate in solid material is between 30 and 80% by volume.

7.- Use of the method according to any one of claims 1 to 6, for the treatment of particulate and / or dissolved pollution of a liquid.

8.- Device for implementing the biological treatment method according to claim 1, characterized in that it consists of a reactor (1) equipped with at least one vertical wall (2) separating the reactor into at least two zones (3, 4, 5) and leaving free passages above and below said wall, comprising a liquid inlet (9) and a liquid collection (11), and a floating bed of particles supporting microorganisms ( 8), as well as a gas blowing device (7) located at the lower part of one of said zones (3, 4, 5).

9.- Device according to claim 8, characterized in that the liquid supply device to be treated (9) is connected to a distribution device (10) of the liquid to be treated at the upper part of the floating bed and that is provided at the bottom of the reactor, below the gas injection device (7), at a phase separation device (12).

10, - Device according to claim 9, characterized in that the phase separation device (12) consists of at least two rows of obstacles arranged in staggered rows.