FR2707183A1 - Process for setting in motion microorganism-carrying particles in a liquid to be treated by a biological route and plant for making use of the process - Google Patents

Abstract

Process for setting in motion microorganism-carrying particles in a liquid to be treated by the microorganisms, characterised in that microorganism-carrying particles (6) of density lower than the density of the liquid to be treated are introduced into a reactor (1) with two zones (3, 4) bounded by a vertical wall (2) leaving free passages below and above the said wall, the reactor is fed with liquid (7) to be treated and a gas (5b) is injected into the lower part of one of the zones (3) of the reactor, so as to establish a concurrent, continuous and ordered circulation of the liquid, solid and gaseous phases in the two zones.

Description

 The invention relates to a method for setting in motion particles carrying microorganisms in a liquid to be treated biologically with said microorganisms, and in particular in the field of biological treatment of waste water, and a biological treatment installation 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 of small particle size allows the maintenance of high concentrations of biomass in biological reactors, also called bioreactors. This ensures higher volume loads and more compact reactors than in conventional processes using free biomass.

 In the prior art of biological treatments using fixed cultures, there are essentially three groups of reactors: fixed bed reactors, three-phase or fluidized bed reactors and turbulent bed reactors.

 Examples of fixed bed reactors are aerated submerged biofilters with granular filling.

Some use granular materials having a density greater than that of water (sand> while others use floating supports (cf. DE-A-25 49 415, GB-A-2 239 192, FR- A-2 498 589, FR A-2 669 917, FR-A-2 670 682, FR-IL-2 673 932>.

 The major drawback of this type of bioreactors is the presence of a considerable part of inactive biomass due to the rapid calming of the bed and the diffusion limitations. It is therefore essential to carry out frequent washes of the fixed bed, washes which interrupt the treatment and produce large quantities of washing water to be recycled or treated specifically.

 Fluidized bed reactors are characterized by a homogeneous expansion of the granular support, ensured by the surface speed of the liquid and controlled by recirculation of the effluent. Such reactors ensure a good mass transfer between the liquid phase and the fixed biomass but the uniform distribution of the hydraulic flow which is of paramount importance requires the development of precise, sophisticated and costly technical devices. However, high yields are obtained and the frequency of bed washing is considerably reduced. However, the fixed biomass is distributed irregularly over the height of the fluidized bed, with accumulation of support particles comprising a very thick biofilm in the upper layers of the bed. This results in a change in the physiological properties of the biomass (in particular a decrease in specific activity) and a change in the physical properties of the particles loaded with biomass which results in their entrainment out of the reactor. FR-8-2 189 328 and US-A-4 322 296, among others, describe systems and devices for controlling the expansion of the bed and for mechanical regulation of the thickness of the biofilm, but the complex nature of all the systems and devices described in the prior art harms the industrial development of this type of reactors. Furthermore, when such a reactor is shut down, the biomass settles and agglomerates around the water distribution devices, which imposes protection of the latter or the possibility at start-up of using considerable energies which can represent up to 10% of aeration energy.

 A variant of the fluidized bed reactors consists of "three-phase fluidized beds" in which the driving force is obtained by simultaneous introduction of the liquid and a gas (EP-A-0 175 568; Trinet et al.

 (Wat.Sci.Tech., 23, 1347-1354; Hosaka et al.

(1991) Wat. Approx. Tech., N "8, 48-51). Due to the high shear forces which then prevail in the reactor, the problem relating to the mechanical control of the thickness of the biofilm is eliminated. However, the problems associated with control of the expansion of the bed and the homogeneous distribution of the flows, which are even more difficult to control. Some of these problems can be resolved by using complex and varied ancillary devices, not otherwise avoiding the restart problems.

 While the three-phase fluidized bed reactors described above use high density granular materials requiring a high energy input for their expansion, other so-called "reverse fluidized bed" reactors have been designed using supports floating granular (DE-A-28 41 011; EP-A- 0 025 309, US-A-4 256 573). In such reactors, the liquid flow and the gas flow circulate in countercurrent, with an expansion of the bed from top to bottom, the expansion being maintained by the motive force of the liquid. Such beds have all the advantages of conventional fluidized beds, and are produced without complex technical devices. They are however limited from the hydrodynamic point of view by the speed of the liquid which must not be too high so as not to disturb the upward movement of the bubbles of the gas and by the speed of the gas which, from a certain flow, cancels the driving force of the liquid by inducing a phenomenon of pseudo-fluidization followed by decantation, for supports having a low density close to that of water.

 The main purpose of the processes using fixed bed and fluidized bed reactors of all the types described above is the accumulation of a high concentration of biomass. However, the development of thick biofilms and the non-uniform distribution of the biomass over the height of the bed alter the biological and hydrodynamic performances that these processes could allow.

 In a third group of reactors, called turbulent bed reactors, a single driving force, that of a gas, is used, which makes it possible to avoid complex liquid distribution systems, with often the need for pretreatment of the raw liquid. to prevent clogging of the distribution system (FR-A-2 342 785; EP-A-0 250 998). The important advantage is obtained of a more homogeneous distribution throughout the reactor of the support and of the fixed biomass. The high shear forces then induce a very high rate of tearing off of the biofilm, but this phenomenon is not controllable and can prevent balanced growth of the latter.

 it was recently proposed by Heijnen et al.

(1992) Wat. Sci. Tech., V.26,, 647-654 to use reactors with ordered circulation of the solid and liquid phases, called "loop reactors" or "reactors of the air-lift type". The shear forces obtained in this type of reactor are moderate and favor a homogeneous development of the biomass fixed on the support particles. However, these support particles have high densities, which affects mass transfer and imposes a limitation of the filling rate of the reactors less than 10% volume / volume, hence a limitation of the available biomass. There is still the problem of the retention of the biomass support in the reactor, implying the use of a more or less complex device for phase separation and the problem of restarting the reactor after stopping operation by using considerable amounts of energy for purging the packed bed by blowing air.

The present invention solves these problems by providing a method of setting in motion particles carrying microorganisms in a liquid to be treated by microorganisms, into which is introduced, into a reactor with two zones delimited by a vertical wall leaving free passages below and above said wall, particles supporting microorganisms, of density less than the density of the liquid to be treated, the reactor is supplied with liquid to be treated, and a gas is blown into the lower part of one of the zones of the reactor , so as to establish in the two zones a cocurrent, permanent and orderly circulation of the liquid, solid and gaseous phases
The use of support particles having a density lower than the density of the liquid to be treated makes it possible to produce a floating bed with the advantages which this presents. during a drop or a stop of 7'insufflation, the bed does not settle at the bottom of the reactor around the air distribution devices, but remains on the surface of the liquid and in this way the restart of circulation does not require a considerable supply of energy, and eliminates the need for a phase separator used to reduce the kinetic energy and retain the support in the reactor. The separation into two zones of the reactor and the introduction of a gas at the lower part of one of the zones means that there is a difference in density between the total fluid of the blown zone and that of the non-blown zone. difference induces a co-current, permanent and orderly circulation of the three liquid, gas and solid phases. Such circulation has important advantages for biological processes. Bulle ensures on the one hand a better mass transfer by avoiding excessive shearing forces, specific to turbulent beds and three-phase fluidized beds. The biomass is constantly in contact with the bubbles of oxygen-supplying gases, undergoing the ordered movement of the liquid flow. Furthermore, low surface gas speeds induce high speeds of circulation of the liquid and of the support, and from there the energy supply necessary to maintain this permanent circulation is lower than that necessary for the other processes with moving beds, in particular the turbulent beds and fluidized beds
One of the advantages that the inventive method provides is the simple and effective control of the thickness of the biofifm. This is obtained due to the ordered and controlled movement of the carrier particles of biomass in co-current: 1) in ascending flow, with the liquid and gas phases in the blown zone and 2) in descending flow, with the liquid phase and a part of the gas phase entrained in the non-blown zone. In this way, the surface of the support particles undergoes only shear stresses due to friction between the phases, without impacts between the particles. These constraints, which are moderate shear forces, ensure a constant rate of tearing off of the biofilm and therefore the maintenance of an optimal thickness. The tearing rate of the bisfiim and consequently the thickness of the biofilm can be adjusted as a function of the speed of circulation of the liquid a) by the speed of the gas in the upward flow compartment which is advantageously maintained between 0.001 and 0.5 m / s, preferably between 0.01 and 0.05 m / s, b) by the ratio between the height and the width of the reactor preferably between 1 and 12, and better still between 4 and 10, and c) by the static height of liquid, relative to the upper level of the separation wall, which is + 0 to + 25X of the total height of the reactor.

 Furthermore, the permanent circulation of the floating support leads to an improvement in the transfer of material. This ensures a significant reduction in diffusional limitations and an increase in the transfer surface between the biomass and the liquid.

On the other hand, given the results of the experimental tests, the presence of a solid phase of low density (real density between 0.65 and 0.97 g / cm) has a positive effect on the transfer up to filling rates which are much higher than those used in the processes with supports having a density greater than 1.0 g / cm3, filling rates which can range from 5 to 50% volume / volume and preferably from 20 to 40% volume / volume, which considerably increases the amount of active biomass in the reactor.

 This ensures maximum activity of the biomass fixed on the support particles and higher reactor yields are thus obtained.

 The setting in motion of the support particles according to the method of the invention also has the advantage of reducing energy consumption. This is due to the fact that the driving force is provided by a gas injection, which is recognized to be very economical. The minimum gas speed, and hence the energy input, for maintaining the circulation of the support particles is much lower than the minimum fluidization speed or the turbulence specific to the other moving bed processes described in prior art. To further improve this advantage, the insufflation takes place in the form of fine bubbles with a uniform distribution over the surface of the insufflated zone. We can also play on the characteristics of the floating support to further reduce the energy supply necessary for maintaining circulation. In this regard, the difference between the density of the chosen product and that of the liquid is preferably less than 0.35 g / cm3 and better still is between 0.03 and 0.20 g / cm3.

 Advantageously, a support is used which does not absorb water and whose surface condition is preferably rough and / or has open pores, in order to promote not only the attachment of microorganisms but also to facilitate continuous renewal. fixed biomass. Various natural or organic synthetic mineral materials (plastics) can be used. By way of example, mention may be made of granular supports of polyethylene or of expanded polypropylene having a particle size of 0.2 to 10 mm, preferably 1 to 2 mm.

 As indicated above, one of the advantages of the method of setting in motion the floating bed of support particles is that, when the airflow decreases or stops, whether these are voluntary or accidental, the energy supply for normal recirculation is low and this normal recirculation is done without any difficulty, unlike what is encountered in fluidized and turbulent beds which require discontinuous operation, protective measures for water distribution devices and high energy consumption starting. One can in particular with the method of setting in motion according to the invention, envisage a periodic drop in the aeration rate (particular case of insufflation), when the water to be treated has a better quality, which is generally the case for wastewater collected and treated during the night periods. We can thus achieve substantial energy savings without compromising the more intense return to operation required for the wastewater collected and treated during the day.

Furthermore, the confinement of a floating material in a reactor does not pose any particular problems and does not require any particular installations. Therefore it is very easy to pass the effluent from a reactor implementing the method of setting in motion 1 according to the invention in subsequent reactors, arranged in series or in parallel, in which treatments are carried out identical or different biological materials and / or in which the movement of the support particles is carried out by other techniques, for example descending fluidized beds, floating beds,
It is further provided according to the present invention an embodiment of a reactor for implementing the method according to the invention for the biological treatment of liquids and in particular waste water, comprising at least two compartments communicating with each other, each of these compartments constituting a reactor with two zones delimited by a vertical wall leaving free passages above and below said wall, at least one of the compartments implementing the method of setting in motion in co-current circulation , permanent and orderly liquid, solid and gaseous phases according to the invention. The implementation in the other compartment (s) of the treatment installation of fluidization or flotation processes of beds makes it possible to carry out in the same compartment reactor successive different biological treatments.

 One can for example consider using a first compartment using a fluidized bed technique, then one or more compartments in which a floating bed with permanent and ordered circulation is used, and a compartment in which a floating bed.

 In such a device, it is possible to carry out successively an aerobic biological treatment at low charge in a fluidized bed, which is particularly suitable for the treatment of carbonaceous materials or denitrification in anoxia in the non-aerated zone; in the compartment or compartments implementing the floating bed with permanent and orderly circulation, it is possible to use aerobic treatment conditions, with a high load of organic matter or for nitrification treatments and finally in a floating bed compartment, without aeration, an anaerobic treatment can be carried out, for example for the phosphate removal of water or an anoxic treatment suitable for denitrification, provided downstream of the installation. A recirculation between the different compartments of the treated water is planned in order to ensure the supply of nutrients necessary for bacterial metabolism by avoiding a significant consumption of chemical reagents (methanol or ethanol for example in conventional schemes).

 On the other hand, the gas released in the compartments can be recovered and reused in the same or in another compartment, in recirculation, to maintain the permanent circulation of the liquid and the support particles in limitation and / or in the absence of oxygen.

 The different operating modes of the fluidized, circulating or floating bed compartments and the oxygen supply to ensure aerobic, anoxic or anaerobic conditions can be reversed and varied during the treatment, thus making it possible to achieve savings in reagents and a better quality of purified water.

 The water treated in one compartment passes into the next through a communication device which makes it possible to avoid short-circuits of untreated water, to ensure the hydraulic residence time necessary for biological processes and to retain the support particles.

Other characteristics and advantages of the invention will appear on reading the detailed description which follows, given with reference to the appended drawings in which
FIGS. 1a, 1b and 1c are examples of reactors allowing the implementation of the process of the invention, and
Figure 2 is an example of a biological treatment installation implementing the method shown schematically in Figures la to lc.

 Figures la to lc show three embodiments of reactors in which identical or similar elements have the same reference numbers (as in FIG. 2).

 In a reactor 1, a vertical wall 2 delimits two zones 3 and 4, communicating with each other by passages above and below the wall 2. An insufflation system 5 located at the bottom of one of the zones, here zone 3, is supplied with air by line 5a (or possibly with air recycled by line 5c. The microorganisms necessary for biochemical transformations, for example for the purification of waste water, are fixed and develop on granular support particles 6 having a density lower than that of the liquid to be treated. The liquid to be treated is introduced via a pipe 7 at the top of the reactor (this positioning of the inlet for the liquid to be treated is given by way of example, the liquid being able to be introduced at any point, for example also at the top of the reactor in the downflow zone). Under the effect of the motive force due to air bubbles 5b, the three phases solid, liquid and gaseous tent in permanent and orderly circulation according to the arrows A. Of course, if the aeration was done in zone 4, the circulation would be in the opposite direction of the arrows A. In the aerated zone 3, the flow is ascending and in the unventilated zone 4 the flow is descending.

 The quantity of air injected into the reactor 1 can be adjusted to control the speed of circulation of the liquid between the two zones, by adjusting the surface speed of the gas between 0.001 and 0.5 m / s. The actual density of the chosen support is preferably 0.03 to 0.35 g / cm3 lower than the density of the liquid to be treated. During its passage through the aerated zone 3, the biofilm formed on the support particles undergoes shear stresses which control its thickness. The ventilated area also has the role of supplying oxygen necessary for aerobic processes. As a considerable part of the air bubbles from the aerated zone 3 is entrained by the high speed of circulation of the liquid towards the non-aerated zone, with a recirculation of 10 to 75% of the gas, there is in the non-aerated zone sufficient oxygen supply for aerobic processes.

 The speed of circulation of the liquid and the supply of oxygen are the two most important parameters of the process and determine the correct functioning of the reactor. They can be controlled on the one hand by the quantity of air injected and on the other hand by the geometric configuration of the reactor. In particular, the geometrical configuration of the reactor is determined 1) by the ratio between the surfaces of the aerated 3 and non-aerated zones 4, which is preferably between 0.5 and 3.0, 2) by the ratio of the height of the reactor at its width which is preferably between i and 12 and 3) by the static height of the liquid. This is located, relative to the upper level of the vertical wall 2, at + O to 25 of the total height of the reactor, or + O at 1 m for a 4 m reactor.

 The raw water to be treated or any other liquid is introduced via line 7 into the reactor 1, at any location, but advantageously at the top of the reactor in the downward zone, without it being necessary to use specific liquid flow distribution devices that require pre-filtration to prevent clogging.

The treated water is evacuated by a siphon 10 and a pipe 11, protected by a weir (not shown) so as to maintain the desired static level of liquid in the reactor 1.

 In the reactor shown in Figure la, the reactor is fully mixed and the effluent is discharged directly from the reaction zone.

 In the variant shown in FIG. 1b, the effluent is evacuated after passing through a stilling or settling zone 8, delimited by deflectors 13; this zone prevents leaching of floating particles from the support and makes it possible to separate the treated water from the biafilm torn from the support particles. A pipe 9 is then provided for the evacuation of the sludge which accumulates at the bottom of the reactor.

 In the variant represented in FIG. 1c, the reactor 1 is fully stirred as in FIG. 1a but the settling zone 8 is constituted by a secondary reactor, independent and outside the reaction zone; the reactor 1 and the decantation zone 8 are connected by a pipe 8a situated below the static level in the reactor 1 and the decantation zone 8, static level which is determined by the siphon 10 and the pipe 11. The advantage of this separate settling zone is to allow the recovery and return to the reactor 1, via line 12, of the floating particles which could have been entrained with the treated water. Such particle entrainment does not normally occur but can result from a malfunction of the reactor.

 The geometric shape of the reactors 1 and of the vertical wall 2 can be freely chosen as long as it allows the realization of two zones in one of which the flow is aerated and ascending and in the other of which the flow is non-aerated and descending . The reactor may have a rectangular base with a flat vertical wall; it can have a circular base with a flat vertical wall, or else with a concentric cylindrical wall. Better results are obtained by using the proportions indicated above.

 Figure 2 shows, in perspective and schematically, a biological treatment installation in which is implemented the movement method described above. For example, the installation shown comprises four unit reactors, but one could consider using installations comprising two or three unit reactors or compartments, or a number greater than four, depending on the number of specific biological treatments that are would like to realize in the same installation.

 As a variant, the unit reactors or compartments could be arranged in parallel or in series in separate reactors but the structure produced in a single reactor with several compartments according to FIG. 2 is particularly advantageous.

 The installation comprises four compartments 20, 21, 22 and 23, each constituting a reactor in which two zones 3 and 4 are delimited by a wall 2.

 It is known that inverted fluidized beds (that is to say in downward flow) are easier to establish than fluidized beds in upward flow and therefore, by adjusting the amount of air injected into the aerated zone 3 compartment 20, can be established in the unventilated area 4 a reverse fluidized bed. The aeration to obtain this reverse fluidized bed ensures an oxygen supply which is suitable, at low volume charges for the elimination of organic carbon and fou denitrification in the event of anoxia in the downflow zone. The liquid thus treated then passes along arrow C under the wall 24 through a device 25 which retains the support particles and prevents possible short circuits of untreated water and which separates the first compartment 20 from the second compartment 21. In compartment 21, as well as in compartment 22 separated from compartment 21 by a partition 24 and device 25 allowing the passage of the liquid only at low speeds and at the bottom of the reactor, there is established a permanent and orderly circulation of the bed floating according to the method of the present invention. By way of example, a circulation according to arrows B has been shown in compartment 21 with reversal of the ventilated zone 3 and of the non-ventilated zone 4 with respect to compartment 20 and a circulation according to arrows A in compartment 22 , but it is understood that the direction of traffic is only of relative importance. If it is desired to continue in compartments 21 and 22 an aerobic process started in compartment 20, an adequate supply of oxygen is established with relatively rapid circulation. This operating mode is particularly suitable for processes with high oxygen requirements. On the other hand, to carry out an anoxic treatment in one of the two compartments, one can be satisfied with a weak ventilation, however sufficient to put the floating bed in permanent and orderly circulation, and for example carry out nitrification in compartment 21 and denitrification in compartment 22. Such poor ventilation can be obtained by reducing the flow of air blown through line 5a or by recycling oxygen-depleted air from the same compartment to a different compartment, via the driving 5c.

 In compartment 23 * the ventilation is interrupted, thereby producing a fixed floating bed, which makes it possible to carry out an anaerobic process, for example of phosphating, and / or to retain the suspended matter.

 A decantation zone 8 is provided between each compartment to avoid significant entrainment of the support particles from one compartment to another, so as to preserve the biological specificity of the support particles confined in each compartment.

In addition to the device 25, a settling zone 8b can be provided between certain compartments to collect the purified water and separate it from the excess biomass and floating particles which would be entrained during a malfunction of the reactor in order to return them to the different compartments. It is understood that a small quantity of support particles carrying a specific biomass can be introduced into a compartment containing a different biomass, the small quantity of biomass introduced acclimating to the new conditions.

 The independent hydraulic operation of each compartment is ensured by a differentiated insufflation system 5. Therefore, the air injection and therefore the phase circulation speed can be adjusted independently. This provides some important and unique advantages to this system. The first advantage consists in the possibility of carrying out different hydraulic regimes which can be adjusted according to hydraulic loads, organic loads or the desired quality of the treated water.

Another advantage is the possibility of implementing various aerobic, anoxic or anaerobic conditions in the different compartments depending on the pollution and the treatment sought. In particular, organic carbon removal, nitrification, denitrification and removal of phosphorus can be carried out in the same reactor. In addition, it is possible to periodically modify the aeration conditions in the various compartments and / or to periodically recycle the treated water from one compartment to another by a liquid recirculation system 14, in order to reduce the consumption of chemical reagents intended to obtain a neutral pH (nitrificationdénitrification) and consumption of carbon source for denitrification.

 The preceding examples have demonstrated the use of the reactors of FIGS. 1a, 1b, 1c and 2, with the use of air for setting the particles in motion.

Interesting variants can be obtained by replacing the air blown into a reactor or compartment
- by the air collected at the outlet of the same compartment or reactor, still sufficiently rich in oxygen to maintain aerobic conditions
- by the gas collected in this same reactor or compartment or another gas too depleted in oxygen to be recycled to an aerobic compartment but usable in a compartment operating in anoxia or anaerobiosis
- by gas (methane or others) formed in other compartments or reactors.

 As an example, a variant of the operation of the compartment reactor of FIG. 2 will be described below, a variant in which it is desired to carry out denitrification in the first compartment.

To maintain the anoxic conditions necessary for denitrification in zone 4 with a fluidized bed descending from compartment 20
- either reduce the amount of air introduced through line 5a into the zone 3 insufflation system
- Or inject into zone 3 the gas depleted in oxygen or even oxygen-free, collected in the upper part of compartment 20 and recycled at 5 by line 5c.

 The liquid having undergone denitrification then passes into compartment 21 where a permanent and orderly circulation of floating bed is established where an aerobic treatment is carried out for the removal of the non-degraded carbon in compartment 21, with an air supply ensuring the biological reaction and maintenance of circulation.

 The liquid then passes into compartment 22 where, with a high supply of oxygen and a relatively rapid circulation of the support obtained by relatively large insufflation of air through line 5a, nitrification is carried out.

 Then in compartment 23 the suspended matter and the biofilm torn out in the preceding compartments are retained by stopping or reducing the insufflation and obtaining a fixed floating bed.

 Each compartment 20 to 23 being provided with an independent insufflation system 5 and connected to a pipe 5a for air injection and to the pipes 5c for recycling the gases collected in the upper part of the compartments, it is possible with a system closing and opening of appropriate valves to freely choose the nature and flow rate of the gas blown into each compartment to produce different hydraulic systems (descending fluidized bed, circulating bed, floating bed) with various conditions (aerobic, anoxic, anaerobic) that you can change, reverse or alternate.

 A very large number of variants can therefore be produced in the same reactor.

Claims (14)

 1.- Method of setting in motion particles supporting microorganisms in a liquid to be treated by microorganisms, characterized in that one introduces, into a reactor (1) with two zones (3,4) delimited by a vertical wall C2 ) leaving free passages below and above said wall, particles (6) supporting microorganisms, of density less than the density of the liquid to be treated, the reactor is supplied with liquid (7) to be treated, and blows a gas (Ub) at the bottom of one of the reactor zones (3), so as to establish in the two zones a co-current circulation, permanent and orderly of the liquid, solid and gas phases.  2.- Method according to claim 1, characterized in that the surface speed of the gas is between 0.001 001 and 0.5 m / s.  3.- Method according to either of claims 1 and 2, characterized in that the difference between the density of the liquid and that of the carrier particles is less than 0.35.  4.- Method according to claim 3, characterized in that said difference is between 0.03 and 0.20.  5.- Method according to any one of claims 1 to 4, characterized in that the static height of liquid, relative to the upper part of the wall separating the reactor into two zones, is from + 0 to + 25 the total height of the reactor.  6.- Method according to any one of claims 1 to 5, characterized in that one uses as support particles a granular material, with a rough surface and / or with open pores, chosen from the group consisting of natural mineral materials or synthetic plastics that do not absorb water.  7.- Method according to any one of claims 1 to 6, characterized in that a rectangular base reactor is used, the vertical separation wall being planar.  8, - Method according to any one of claims 1 to 6, characterized in that a circular base reactor is used, the vertical wall being cylindrical and concentric.  9.- Method according to either of Claims 7 and 8, characterized in that the ratio between the height and the width of the reactor is between 1 and 12.  10.- Method according to any one of claims 1 to 9, characterized in that the blown gas is air.  il.- A method according to any one of claims 1 to 9, characterized in that the blown gas is the gas collected in the upper part of the reactor (1).  12.- Method according to any one of claims 1 to 9, characterized in that the blown gas is the gas collected in the upper part of another reactor (1)  13.- Biological treatment installation characterized in that it comprises at least two compartments communicating with each other, each of these compartments comprising an individual insufflation system <5) and constituting a reactor (i) with two zones C3,4) delimited by a vertical wall C2) leaving free passages above and below said wall, at least one (21, 22) of the compartments implementing the method according to any one of claims 1 to 10.  14. Biological treatment installation according to claim 12, characterized in that it comprises a first compartment (20) in which a fluidized bed of support particles is established, the liquid leaving the first compartment being sent into a second compartment (21 ) in which the method according to any one of claims 1 to 9 is implemented, the liquid obtained being sent, optionally after passage into another compartment (22) operating in the same manner as the second compartment, in a last compartment (23) operating in a fixed floating bed.  15.- Installation. According to claim 14, characterized in that the first compartment (20) is supplied with air, optionally with recycled air, by a supply line (5a) or a recycling line (5c) and ensures l elimination of organic carbon, the second compartment (21) is supplied with air via line <5a> and provides nitrification, the third compartment (23) is supplied with air, possibly oxygen-free gas, recycled through the line <5c) to carry out denitrification, and the fixed floating bed in the last compartment (23) retains the suspended matter and the biofilm torn off.  16.- Installation according to claim 14, characterized in that the first compartment (20) is supplied with air in reduced quantity by a supply pipe (5a) or by recycled gas by a pipe (5c) from a or several compartments (20,21,22,23) to carry out a denitrification, the second compartment (21) is supplied with sufficiently oxygenated air by a supply or recycling line C5a, 5c) to effect the removal of organic carbon , the third compartment (22) is supplied with air by a supply line (5a) for carrying out nitrification and the fixed floating bed in the last compartment C23) retains the suspended matter and the biofilm torn off.  17 - Installation according to any one of claims 14 to 16, characterized in that it comprises an additional zone (8b) at the outlet of the last compartment (23>, for recovering the support particles which could have escaped.