FR2781785A1 - METHOD FOR THE BIOLOGICAL TREATMENT OF NON-OR LITTLE OR EXCESSIVE SLUDGE EFFLUENTS INCLUDING A FIXED BIOMASS TREATMENT STAGE - Google Patents

Abstract

Process for the biological treatment of effluents producing little or no excess sludge including a step of treatment by fixed biomass.The invention relates to a process for treating an effluent with a view to its purification comprising at least one step of biological treatment (1) leading to the production of biological sludge, characterized in that at least part of the biomass used during said biological treatment step is fixed on a support and in that it comprises at least one step (2) consisting in subjecting at least part of said sludge from said biological treatment step to conditioning aimed at improving their biodegradability and a step (3) consisting in redirecting the sludge thus conditioned to said biological treatment step.

Description

Process for the biological treatment of effluents which do not produce or

  little excess sludge including a fixed biomass treatment step.

  The invention relates to the field of biological treatment of effluents with a view to their purification, such as in particular, but not exclusively, urban or industrial wastewater. There are various types of biological treatment for water pollution. These treatments are based on the ability of the biomass to eliminate biodegradable pollution: by assimilating it into the bacterial flock, whose total mass in the treatment system is maintained at an optimum level, by extracting excess sludge , - by transforming it into gaseous molecules (C02 for carbon pollution and N2 for nitrogen pollution via the nitrification of nitrogen NTK to nitrates by the nitrifying biomass, and the subsequent denitrification of nitrates into atmospheric nitrogen by

denitrifying biomass).

  Biological pollution treatment systems therefore reject: treated water, returned to the receiving environment; - gaseous molecules (mainly C02 and N2, CH4 also, especially for digestion treatments), which are sent to the atmosphere, directly, or after combustion for CH4; - excess sludge, mainly consisting of biomass produced during

  treatment and, on the other hand, non-biodegradable decantable pollution.

  One of the major problems in wastewater treatment is the fate of the sludge extracted from the system. Their high organic content often makes them unacceptable in landfills. Their spreading in agriculture is supervised by

  increasingly stringent regulations making this route increasingly expensive.

  To cope with the constantly increasing quantity of this excess biological sludge, and with the problem of their final devolution, various techniques have been proposed to enable the volumes of sludge to be removed to be reduced. Among these techniques, mention may be made in particular of incineration and drying. However, these techniques require the costly installation of increasingly sophisticated smoke treatment systems in order to

  protect the atmosphere from pollution.

  In this context, the idea was born of reducing sludge production to the minimum possible, if possible up to the "zero sludge produced" level, by conditioning all or part of the sludge before recycling at the head of biological treatment, so as to allow biological reprocessing of this sludge eliminating, in gaseous or dissolved mineral form, the equivalent by weight of the excess sludge which, without this treatment, should have been

theoretically extracted from the system.

  Numerous ways of treating sludge before recycling are thus described in the literature, making it possible to condition the sludge so as to facilitate its biological elimination, mainly in the form of atmospheric C02, by

  reprocessing in the system that produced them.

  Among these sludge conditioning routes, we can cite: - various thermal treatments of sludge by simply raising the temperature in processes which dissolve part of the biomass by bursting of the cell walls and thermal hydrolysis of molecules which are difficult to biodegradable; treatments based on the action of oxidizing agents, such as the process described in European patent application EP-A-0 645 347 which proposes to act on ozone on the mixed liquor recirculated in the biological basin in order to reduce the production of excess sludge; treatments of the chemical type, such as, for example, acid hydrolysis treatments of part of the sludge before recycling, which can make it possible to break chains of the cellulosic type and transform them into sugars or other easily biodegradable products; - mechanical type treatments such as in particular those described in American patents US-A-5,240,599, US-A -5,282,980 and US-A-5,522,553, using various techniques allowing the bursting of cell walls, such as, for example, fine grinders (of the type used for the production of pigments for example), or ultrasonic grinders, or even techniques for control of instantaneous sludge depression at high temperature; - other methods allowing such conditioning, including those

  combining some of the previously mentioned methods to improve their effectiveness.

  All these methods have in common the fact that in order to eliminate from the system a given quantity X of sludge, corresponding to the elimination of the pollution entering the system for a given time, for example a day, they require biologically inactivating, during conditioning, a quantity of sludge greater than X, by a factor k which depends, in particular, on the efficiency of the conditioning method used. Those skilled in the art know that, to eliminate a given type of pollution, it is necessary to maintain the sludge in the biological system for a given period of time, called the "mud age", which is from a few days to a ten days in the treatment of carbonaceous pollution by medium-charge activated sludge, for example, and frequently around 20 days in the treatment of nitrogen pollution by low-charge activated sludge, so as to maintain conditions favoring autotrophic nitrifying bacteria in the system , which have a long doubling period, compared to heterotrophic bacteria treating carbon and nitrates, which have a short doubling period. The age of the sludge is equal to the weight of sludge contained in the sludge tank

  activated, divided by the weight of sludge extracted (or inactivated) during a day.

  Thus, in a given volume of activated sludge from which X kg of sludge is extracted each day with an initial sludge age of T, the sludge age will become T / k when it is sought to biologically eliminate the X kg of sludge produced daily in

  daily conditioning k * X kg of sludge before recycling to biological treatment.

  For a value of k equal to 3, for example, the age of sludge will be divided by 3 in the system if we want to totally eliminate the production of sludge by packaging and recycling. In addition to the increase in basin size linked to the increase in the quantity of pollution to be treated due to the recycling of sludge conditioned to be biodegradable, it will be necessary, to keep the treatment effective, to keep the age of the activated sludge constant. To do this, we can: - either maintain the constant concentration in the basin but multiply by a factor k the volume of the treatment basin; - either keep the pool volume constant by increasing the concentration of

sludge in the basin.

  In the case of the treatment of carbonaceous and nitrogenous pollution by activated sludge known as "low charge", or "prolonged aeration", which require substantial mud ages and therefore large volumes of basin, the expense resulting from the need to increase the size of the basins by a factor k of the order of 3, for example, is very large, and can considerably reduce the economic benefit of reducing

sludge production.

  A method has been described for keeping a sufficient age of sludge in the system without appreciably increasing the volume of the activated sludge tank: this method consists in extracting the treated water from the activated sludge tank through a membrane surface retaining the sludge in the basin. It then suffices to increase the concentration of sludge in the basin to maintain the age of activated sludge at the desired value, taking into account the quantity of known sludge "deactivated" daily by the conditioning and reinjection process in the basin. It is a method well suited to small units requiring very good quality of leaving water, but economically uncompetitive for use in large treatment units. The objective of the present invention is to propose a method making it possible to reduce the amount of excess sludge conventionally produced during a biological treatment of water which does not have the above-mentioned drawbacks of

  state of the art processes.

  In particular, an objective of the present invention is to propose such a method making it possible to reduce to a minimum the need to increase the size of installations for treating carbon and / or nitrogen and / or phosphate pollution, while maintaining the treatment system. sludge in quantity and quality compatible with

treatment goals required.

  Another objective of the present invention is to describe such a process making it possible, under certain conditions, not to generate an excess of biological sludge ordinarily produced by the processes of the state of the art, that is to say say offering the opportunity to

  completely eliminate the production of excess sludge.

  Yet another object of the present invention is to disclose installations

  for the implementation of such a method.

  These various objectives, as well as others which will appear subsequently, are achieved thanks to the invention which relates to a process for treating an effluent with a view to its purification comprising at least one step of biological treatment leading to the production of biological sludge, characterized in that at least part of the biomass used during said biological treatment step is fixed on a support and in that it comprises at least one step consisting in subjecting at least a part of said sludge from said biological treatment step, packaging aimed at improving their biodegradability and a step consisting in re-routing the sludges thus conditioned

  towards said biological treatment step.

  The invention therefore consists in combining the use of a biological treatment process comprising at least one biomass treatment step fixed on a support material with a treatment improving the biodegradability of the sludge, carried out on all or

  part of the sludge leaving the system or during its recycling.

  This combination makes it possible to maintain a sludge age in accordance with the treatment requirements in the fixed biomass stage, without affecting this sludge fixed by the conditioning applied to "free" sludge, that is to say the unbound sludge and the

  excess sludge removed during washing.

  Preferably, said conditioning step is chosen from the group consisting of: heat treatments with or without oxygen injection, disintegration treatments using mechanical means and / or ultrasound, oxidation treatments using ozone and / or peroxide

  hydrogen, acid or basic hydrolysis treatments.

  Also preferably, said fixed biomass is used in at least one device chosen from the group consisting of biofilters (such as in particular those marketed by the Applicant under the names Biocarbon, Biostyr, B2A), bacterial beds, fluidized beds ( such as that marketed by the Applicant under the name Biolift), floating support devices in which we add

  a floating support material in an activated sludge.

  According to an advantageous variant of the invention, the method includes a step of nitrifying said effluent using a fixed biomass and one or more other

  biological treatment steps using free biomass.

  In such a preferred version, the invention combines the use of a nitrification treatment step with bacteria attached to one or more denitrification steps and / or treatment of carbon pollution by free bacteria, of the anoxic activated sludge type,

  for example, with or without, but preferably without, primary decantation step.

  This version has the advantage of optimizing the cost of the processing system by

  not fixing on a fixed biomass system - more expensive than the activated sludge system -

  that autotrophic nitrifying bacteria, which require a consistent sludge age but produce little sludge, while heterotrophic denitrifying and / or treating carbon pollution sludge - which constitute the main production of sludge in the system - are maintained in a relatively small size activated sludge type system due to the high growth rates of this type of sludge, and the increase in

  pruning will remain relatively inexpensive.

  Only excess nitrifying sludge is then treated, and all or part of the

recycled activated sludge.

  This version also has the unforeseen advantage, by maintaining fairly long hydraulic residence times in the system, of allowing better biodegradation of the sludge conditioned in the tank of activated sludge before it passes

  on the fixed biomass nitrifying device.

  In a variant having the advantage of maintaining the continuity of the process, the

  nitrifying bacteria are fixed on a material placed in fluidization.

  In a variant allowing the water to be filtered before discharge, the anoxic zone and the clarifier are followed by a nitrifying biofilter. Part of the anoxic sludge from the clarifier is conditioned before recycling, as well as all or part of the washing water.

  from the nitrifying biofiltration stage.

  In a variant well suited to the rehabilitation of existing installations, the nitrifying bacteria will be fixed on a floating support material in the activated sludge tank. According to a variant, the method according to the invention can comprise a denitrification step by free biomass, a step of clarification of the mixed liquor coming from said denitrification step, a step of nitrification of the clarified effluent thanks to a fixed biomass, a step of recycling the nitrates to said denitrification step and a step of conditioning at least a portion of the sludge from said clarification step as well as optionally at least a portion of the nitrifying sludge

  excess from said nitrification step (washing sludge).

  According to another variant, the method according to the invention can comprise a step of denitrification of the effluent by free biomass, a step of nitrification of the mixed liquor originating from said denitrification step in an aerated reactor using a fixed biomass, a step of recycling part of the mixed liquor from said nitrification step to said denitrification step, a step of clarifying another part of the mixed liquor from said nitrification step, a packaging step of at least part of the sludge from said clarification step and a step of recycling the conditioned sludge to said denitrification step. According to another variant, the method according to the invention may comprise a step of denitrification of the effluent in a reactor using a fixed biomass, a step of nitrification of the mixed liquor originating from said denitrification step in an aerated reactor putting using a fixed biomass, a step of recycling part of the mixed liquor from said nitrification step to said denitrification step, a step of conditioning at least part of the sludge from said denitrification step and said nitrification step, and a recycling step

  sludge conditioned to said denitrification step.

  According to yet another variant, the method according to the invention can comprise a step of denitrification of the effluent in a reactor using a fixed biomass, a step of nitrification of the mixed liquor coming from said denitrification step in an aerated reactor using a fixed biomass, a step of recycling part of the mixed liquor coming from said nitrification step towards said denitrification step, a step of clarifying the mixed liquor coming from the nitrification step, a step of conditioning of at least part of the sludge from said clarification step, and a sludge recycling step

  conditioned towards said denitrification step.

  Also according to a variant, the method comprises at least one step of anaerobic biological treatment implemented using a biomass fixed on a fixed or fluidized bed, at least part of the excess sludge coming from said anaerobic step being

  conditioned before being redirected to said biological treatment step.

  The invention also relates to installations specially designed for implementing the method described above, comprising at least one biological treatment device using a biomass fixed on a support, at least one unit for packaging at least one part of the sludge from said biological treatment device and the means for recycling the conditioned sludge to said

  biological treatment device.

  Advantageously, said fixed biomass device is chosen from the group consisting of biofilters, bacterial beds, fluidized beds, floating support devices. Also advantageously, said conditioning unit is chosen from the group consisting of heat treatment units with or without oxygen injection, the disintegration treatment units using mechanical and / or ultrasound means, the treatment units of oxidation using ozone and / or

  hydrogen peroxide, acid or basic hydrolysis treatment units.

  According to a variant of the invention, the installation comprises at least one activated sludge pool used in particular to denitrify said effluent, at least one clarifier recovering the mixed liquor coming from said activated sludge pool, at least one treatment device for biomass fixed on a support used to nitrify the clarified effluent, means for recycling the mixed liquor from said device, and at least one unit for conditioning at least part of the sludge from said clarifier as well as nitrifying sludge in excess from said device for nitrifying the effluent, and from the means for recycling the conditioned sludge

  towards said activated sludge pool.

  According to another variant, the installation comprises at least one activated sludge tank used in particular to denitrify said effluent, at least one biomass treatment device fixed on a support used to nitrify the effluent coming from said sludge tank activated, at least one clarifier recovering part of the mixed liquor coming from said fixed biomass treatment device, means for recycling the other part of the mixed liquor coming from the fixed biomass treatment device, at least one packaging unit at least part of the sludge from said clarifier, means for recycling the conditioned sludge to said

activated sludge tank.

  Advantageously, said activated sludge pool comprises at least one zone

  anoxia, preceded and / or followed by at least one ventilated area.

  Also advantageously, said activated sludge pool comprises at least

  an anaerobic zone provided upstream of said aerated and anoxic zone (s).

  According to another variant, the installation comprises at least a first biomass treatment device fixed on a support used to denitrify the effluent, at least a second biomass treatment device fixed on a support used to nitrify the effluent from said first device, means for recycling part of the mixed liquor from said second device to said first device, at least one unit for packaging at least part of the sludge from said second device, and means recycling conditioned sludge to said first device. According to yet another variant, the installation comprises at least a first biomass treatment device fixed on a support used to denitrify the effluent, at least a second biomass treatment device fixed on a support used to nitrify the effluent from said first device, means for recycling part of the mixed liquor from said second device to said first device, at least one clarifier for the mixed liquor from said second device, at least one packaging unit for at least part of the sludge from said clarifier, and means for recycling the conditioned sludge to

said first device.

  The method according to the invention, as well as the various advantages which it presents,

  will be more easily understood thanks to the description which follows of seven modes of

  realization of installations for the implementation thereof described with reference to

  Figures 1 to 7. In this description, the elements fulfilling identical functions or

  similar are designated by the same references.

  Referring to Figure 1, the installation shown comprises a biological treatment device 1 using a biomass fixed on a support comprising, conventionally a supply 10 of effluent to be purified, an outlet 11 of the treated effluent and a discharge 12 of the washing sludge which is collected in a

  reservoir 13, as well as ventilation means 15.

  In this embodiment, the biological treatment device 1 using a biomass fixed on a support is constituted by a biofilter la, using a layer of granular material more dense than water. Note that in other embodiments, such a biofilter may have one or more layers

  granular materials with densities lower or higher than that of water.

  The installation also includes a unit 2 for conditioning part or all of the sludge from the reservoir 13 used to increase the biodegradability of this sludge and recycling means 3 making it possible to recycle the sludge thus conditioned in the biofiltrela. A pipe 14 is provided for conveying part of the sludge coming from the tank 13 directly (without treatment of

  conditioning) to the biofilter if necessary.

  Referring to Figure 2, the installation shown comprises a biological treatment device 1 using a biomass fixed on a support comprising, conventionally a supply 10 of effluent to be purified and an evacuation 16 of the

  mixed liquor from this device.

  In this embodiment, the biological treatment device 1 using a biomass fixed on a support is constituted by a basin of activated sludge lc in which the biomass is fixed on a floating material constituted by cubes of foam floating in the basin . This activated sludge tank is provided with means

ventilation 15.

  The installation shown also includes a clarifier 5 in which the mixed liquor from the basin lc is sent through a pipe 16, in order to separate the excess sludge and the treated effluent. The excess sludge from the clarifier 5 is conditioned in a conditioning unit 2 before being recycled into the basin lc by recycling means 3. A pipe 14 is also provided for conveying a portion of the sludge from the clarifier 5

  directly (without conditioning treatment) to the LC basin if necessary.

  With reference to FIG. 3, the installation shown comprises a pool of activated sludge 4 with free biomass comprising a supply 10 of effluent to be treated and an evacuation 16 of part of the mixed liquor. Such a basin is used to denitrify the effluent and as such comprises an anoxic zone and a recirculation loop 6 of a

another part of the mixed liquor.

  The installation also includes a clarifier 5 in which part of the mixed liquor from the denitrification tank 4 is sent through a pipe 16, in order to separate the excess sludge and the effluent therefrom. The excess sludge from the clarifier 5 is conditioned in a conditioning unit 2 before being recycled into the denitrification tank 4 by recycling means 3. A pipe 14 is also provided for transporting part of the sludge from the clarifier 5 directly (without conditioning treatment) to pool 4 if necessary. The installation also includes a biological treatment device 1 using a biomass fixed on a support in which the effluent from the clarifier is conveyed. Such a device makes it possible to nitrify the effluent and as such is provided with means for 'aeration. In this embodiment, the device 1 for biological treatment using a biomass fixed on a support consists of a biofilter 1a, using a layer of granular material. A line 20 is provided for conveying the washing sludge from this device to the

conditioning 2.

  With reference to FIG. 4, the installation shown is identical to that described with reference to FIG. 3 except that the device using a biomass fixed on a support consists of a reactor 1b using a fluidized granular material by air injection (like the reactor marketed under the BIOLIFT brand by

  the Applicant or any other similar reactor).

  With reference to FIG. 5, the installation shown comprises a pool of activated sludge 4 with free biomass comprising a supply 10 of effluent to be treated and an evacuation 16 of the mixed liquor. Such a basin is used to denitrify the effluent and at this

title includes an anoxic zone.

  The installation also includes a biological treatment device 1 using a biomass fixed on a support in which the mixed liquor from the denitrification tank 4 is routed. Such a device makes it possible to nitrify the effluent and, as such, is provided aeration means and a recirculation loop 6a of part of the mixed liquor at the head of the tank 4. In this embodiment, the device 1 for biological treatment using a biomass fixed on a support consists by a reactor 1b using a granular material fluidized by air injection, as produced in the BIOLIFT reactor of the Applicant or by any other similar means. The installation also includes a clarifier 5 into which the other part of the mixed liquor from the denitrification tank 4 is sent, in order to separate the excess sludge and the purified effluent. The excess sludge from the clarifier 5 is conditioned in a conditioning unit 2 before being recycled into the denitrification tank by recycling means 3. A pipe 14 is provided for conveying a portion of the sludge coming from the clarifier 5 directly (without treatment

  conditioning) to pool 4 if necessary.

  It will be noted that the anoxic zone of the denitrification basins 4 included in the installations shown with reference to FIGS. 3 to 5, may be preceded and / or followed by at least one aerated zone and preceded by at least one anaerobic zone, with the necessary recycling of mixed liquor With reference to FIG. 6, the installation shown comprises a first device using a biomass fixed on a support and consisting of a biofilter ld using a layer of granular material. Such a biofilter ld is used to denitrify the effluent. The installation also comprises a second biofilter using it a biomass fixed on a support in which the effluent from the first biofilter ld is routed. Such a biofilter allows it to nitrify the effluent and as such is provided with aeration means. The excess sludge coming from the first biofilter ld and from the second biofilter la is conditioned in a conditioning unit 2 before being recycled into the first biofilter ld by recycling means 3. A pipe 14 is also provided for transporting part of the sludge from the second biofilter directly

  (without conditioning treatment) to the first ld biofilter if necessary.

  Referring to FIG. 7, the installation shown comprises a first device using a biomass fixed on a support and constituted by a fluidized bed device using it a layer of granular material. Such a fluidized bed device is used to denitrify the effluent. The installation also comprises a second fluidized bed device 1b employing a biomass fixed on a granular material in which the effluent coming from the first fluidized bed device 1c is routed. Such a device 1b makes it possible to nitrify the effluent and as such is provided with ventilation means. Part of the mixed liquor from nitrification is recycled

  in denitrification by a pipe 6a.

  The installation also includes a clarifier 5 provided at the outlet of the second fluidized bed device 1b. The sludge from this clarifier 5 is conditioned in a conditioning unit 2 before being recycled into the first fluidized bed device 1a by recycling means 3. A line 14 is also provided for conveying part of the sludge from the second directly biofilter it (without treatment of

  conditioning) to the first biofilter ld if necessary.

  The embodiments of the installations described in the examples above are not intended to reduce the scope of the invention. It can therefore be brought there from

  numerous modifications without departing from the framework thereof.

Claims (18)

  1. A method of treating an effluent with a view to its purification comprising at least one step of biological treatment leading to the production of biological sludge, characterized in that at least part of the biomass used during said step of biological treatment is fixed on a support and in that it comprises at least one step consisting in subjecting at least part of said sludge from said biological treatment step to conditioning aimed at improving their biodegradability and a step consisting in re-routing the sludge as well conditioned towards said biological treatment step. 2. Method according to claim 1 characterized in that said conditioning step is chosen from the group consisting of: heat treatments with or without oxygen injection, disintegration treatments using mechanical means and / or ultrasound, oxidation treatments using   ozone and / or hydrogen peroxide, acid or basic hydrolysis treatments.   3. Method according to claim 1 or 2 characterized in that said fixed biomass is implemented in at least one device chosen from the group consisting of   biofilters, bacterial beds, fluidized beds, floating support devices.   4. Method according to any one of claims 1 to 3 characterized in that it   includes a step of nitrifying said effluent using a fixed biomass and a   or several other biological treatment steps using free biomass.   5. Method according to claim 4 characterized in that it comprises a denitrification step by free biomass, a step of clarification of the mixed liquor from said denitrification step, a step of nitrification of the clarified effluent using a biomass fixed, a step of recycling the nitrates to said denitrification step and a step of conditioning at least a portion of the sludge from said clarification step as well as possibly at least a portion of the nitrifying sludge   excess from said nitrification step.   6. Method according to claim 4 characterized in that it comprises a step of denitrification of the effluent by free biomass, a step of nitrification of the mixed liquor originating from said denitrification step in an aerated reactor using a fixed biomass , a step of recycling part of the mixed liquor from said nitrification step to said denitrification step, a step of clarifying another part of the mixed liquor from said nitrification step, a conditioning step of 'at least part of the sludge from said clarification step and a step of recycling the conditioned sludge to said denitrification step.   7. Method according to any one of claims 1 to 3 characterized in that it   comprises a step of denitrification of the effluent in a reactor using a fixed biomass, a step of nitrification of the mixed liquor originating from said step of denitrification in an aerated reactor using a fixed biomass, a step of recycling part of the mixed liquor from said nitrification step to said denitrification step, a step of conditioning at least a part of the sludge from said denitrification step and said nitrification step, and a   step of recycling the conditioned sludge towards said denitrification step.   S15 8. Method according to any one of claims 1 to 3 characterized in that it   comprises a step of denitrification of the effluent in a reactor using a fixed biomass, a step of nitrification of the mixed liquor originating from said step of denitrification in an aerated reactor using a fixed biomass, a step of recycling part of the mixed liquor from said nitrification step to said denitrification step, a step of clarifying the mixed liquor from the nitrification step, a step of conditioning at least part of the sludge from said step clarification, and a sludge recycling step   conditioned towards said denitrification step.   9. Method according to one of claims 1 to 8 characterized in that it comprises at   at least one step of anaerobic biological treatment implemented using a biomass fixed on a fixed or fluidized bed, at least part of the excess sludge coming from said anaerobic step being conditioned before being redirected to said step of biological treatment. 10. Installation specially designed for implementing the method according to one   claims 1 to 9 characterized in that it comprises at least one device (1) for   biological treatment using a biomass fixed on a support, at least one unit (2) for conditioning at least part of the sludge from said device (1) for biological treatment and means for recycling (3) the sludge conditioned to   said biological treatment device (1).   11. Installation according to claim 10 characterized in that said fixed biomass device is chosen from the group consisting of biofilters (la), the beds   bacteria, fluidized beds (lb), floating support devices (lc).   12. Installation according to one of claims 10 or 11 characterized in that said   conditioning unit (2) is chosen from the group consisting of heat treatment units with or without oxygen injection, disintegration treatment units using mechanical and / or ultrasound means, heat treatment units oxidation using ozone and / or hydrogen peroxide,   acid or basic hydrolysis treatment units.   13. Installation according to one of claims 10 to 12 characterized in that it   comprises at least one activated sludge tank (4) used in particular to denitrify said effluent, at least one clarifier (5) recovering the mixed liquor coming from said activated sludge tank (4), at least one treatment device (1) with biomass fixed on a support used to nitrify the clarified effluent, recycling means (6) of the mixed liquor coming from said device (1), at least one conditioning unit (2) of at least part of the sludge from said clarifier (5) as well as possibly from at least part of the excess nitrifying sludge coming from said device for nitrifying, and means for recycling (3) the conditioned sludge   towards said activated sludge pool (4).   14. Installation according to one of claims 10 to 12 characterized in that it   comprises at least one activated sludge tank (4) used in particular to denitrify said effluent, at least one biomass treatment device (1) fixed on a support used to nitrify the effluent coming from said activated sludge tank ( 4), at least one clarifier (5) recovering part of the mixed liquor from said device (1) for processing fixed biomass, recycling means (6a) of the other part of the mixed liquor from device (1) of fixed biomass treatment, at least one conditioning unit (2) of at least part of the sludge coming from said clarifier (5), recycling means (3) of the sludge conditioned towards said basin of activated sludge.   15. Installation according to one of claims 13 or 14 characterized in that said   activated sludge pool includes at least one anoxic zone, preceded and / or followed by at minus a ventilated area.   16. Installation according to claim 15 characterized in that said activated sludge pool comprises at least one anaerobic zone provided upstream of said aerated zone (s) and anoxic (s).   17. Installation according to any one of claims 10 to 12 characterized in that   that it comprises at least a first biomass treatment device (ld) fixed on a support used to denitrify the effluent, at least one second biomass treatment device (la) fixed on a support used to nitrify the effluent from said first device (ld), means for recycling (6a) part of the mixed liquor from said second device (la) to said first device (1 d), at least one conditioning unit (2 ) at least part of the sludge from said second device, and means for recycling (3) the conditioned sludge to said first device.   18. Installation according to any one of claims 10 to 12 characterized in that   that it comprises at least a first biomass treatment device (le) fixed on a support used to denitrify the effluent, at least a second biomass treatment device (lb) fixed on a support used to nitrify the effluent from said first device (le), means for recycling (6a) part of the mixed liquor from said second device (lb) to said first device (le), at least one clarifier (5) of the mixed liquor from said second device (1b), at least one conditioning unit (2) for at least part of the sludge from said clarifier, and means for recycling (3) the sludge conditioned to said first device.