WO2011054401A1

WO2011054401A1 - Bacterial composition for treating blood-containing fatty effluents

Info

Publication number: WO2011054401A1
Application number: PCT/EP2009/064827
Authority: WO
Inventors: Sophie Gendrault; Abdelkader Guellil
Original assignee: Akaeno Sas
Priority date: 2009-11-09
Filing date: 2009-11-09
Publication date: 2011-05-12
Also published as: EP2499099A1

Abstract

The present invention relates to a bacterial composition for treating blood-containing fatty effluents, comprising: a first mixture including i) at least one bacterial strain having lipolytic activity, ii) at least one bacterial strain having haemolytic activity, and iii) at least one bacterial strain having nitrifying activity; and a second mixture including at least one bacterial strain having denitrifiying activity. The invention also relates to a method for treating effluents that implements said composition. The invention can be used in the treatment of industrial effluents charged with organic fatty materials of animal origin and blood, in particular effluents from the food and agri-food industries.

Description

BACTERIAL COMPOSITION FOR TREATMENT

BLOOD EFFLUENTS CONTAINING BLOOD

The present invention belongs to the field of pre-treatment of industrial effluents, in particular effluents from processes used in the food industry, agribusiness.

It relates to a bacterial composition and its implementation in a process for the treatment of such effluents and relates more particularly to a pre-treatment process of effluents loaded with organic fats of animal origin and blood, such as those from slaughterhouse activity, using a selected bacterial cocktail.

It is recalled that during the slaughter of animals, the blood, considered as a waste, is collected to be treated separately from the effluents generally designated wastewater. However, some operations such as the cleaning of rooms and slaughter equipment, generate effluents loaded with blood and animal fat, which can not easily be separated. However, the concentration of fats and nitrogen in these cleaning waters is too high to allow direct discharge to the treatment plant. In fact, there are fat concentrations expressed in MEH (hexane extractable materials) of the order of 400 to 2000 mg / l, a COD (chemical oxygen demand) of the order of 2,000 to 10,000 mg / l. Suspended materials (MEST) are also present at 2,000 to 4,000 mg / l and a total nitrogen concentration in the range of 300 to 800 mg / l. These values far exceed acceptable standards for wastewater treatment plant discharge. It is therefore necessary to perform a treatment to reduce the fat and blood content of these effluents before their evacuation.

The currently used solutions are generally based on a two-step technique, so as to first eliminate fats, and to treat other organic compounds and nitrogen compounds in a second time.

To do this, we first proceed to a separation of fat by flotation and their evacuation for incineration or recovery on a site outside the industrial site. This generates a significant cost of transportation, a cost of disposal, not to mention the negative ecological impact.

The defatted effluent can then undergo a biological or physicochemical treatment to treat the remainder of the COD and total nitrogen. Several biological treatments are now available on the market and can eliminate organic and nitrogen pollution more or less effectively. They rely mostly on the use of activated sludge: a mixture rich in microorganisms of non-specific bioactivities is introduced into the reactors to degrade suspended or dissolved organic matter. This technique has the disadvantage of generating large quantities of sludge at the outlet, which must then be treated separately.

The problem that the present invention wishes to solve is therefore to overcome the various aforementioned drawbacks by proposing a specific bacterial composition and a method implementing it, which makes it possible to treat on a single installation, the different types of pollution present in the water. used in the food and agri-food industry. Another object of the invention is to minimize waste handling and maintenance with a simple process operating continuously. Another object of the invention is to obtain at the outlet an effluent that can be directly supported by a municipal wastewater treatment plant. Yet another object of the invention is to reduce the production of sludge requiring further further processing.

The proposed solution, based on the use of bacterial cocktails in two successive reactors, meets these disadvantages. It allows the concomitant treatment of the different fractions contained in the wastewater from the slaughter of the animals on a single installation, continuously and directly on the industrial site which generates them, without formation of sludge at the exit.

The present invention provides the use of bacteria having selected bioactivities to provide targeted biochemical reactions with high yield. Individually selected bacteria could be combined into a cocktail without losing their activity level. The strains were selected so that they could grow together harmoniously, and without any population regression being observed. Thus, the different populations rub shoulders, develop, and effectively ensure the reactions for which they were selected, allowing an optimum reduction efficiency in a reduced time compared to processes using non-specific activated sludge. The use of specific microorganisms, also selected for their low growth rate, also prevents the production of sludge. These two aspects make the process economical compared to the biological processes currently proposed.

The invention thus constitutes a high-performance, inexpensive and reliable technique that fully meets the regulatory requirements for the pre-treatment of fat and blood-laden effluents before they are discharged into the wastewater drainage system, with greater respect to the environment.

More specifically, the subject of the invention is a bacterial composition for the treatment of fatty effluents containing blood, consisting of:

a first cocktail comprising i) at least one bacterial strain with lipolytic activity, ii) at least one bacterial strain with hemolytic activity, and iii) at least one bacterial strain with nitrifying activity, and

a second cocktail comprising at least one bacterial strain with denitrifying activity. The term "lipolytic bacteria" is a bacterium whose activity leads to the breakdown of fats, in particular by the hydrolysis and beta-oxidation of triglycerides. The term "hemolytic bacteria" is a bacterium whose activity produces complete hemolysis. It is called "nitrifying bacteria", a bacterium whose activity transforms the ammoniacal nitrogen from the degradation of proteins into nitrites and nitrates (nitrification). Lipolytic, haemolytic and nitrifying bacteria which develop under aerobic conditions are used in the present invention.

Denitrifying bacterium is a bacterium whose activity carries out the denitrification stage, which allows nitrates to be converted into nitrogen gas. In the present invention, denitrifying bacteria are used under anoxic conditions.

The first cocktail is therefore a combination of bacteria that is capable of carrying out, under aerobic conditions, both the degradation of fats, a first digestion of blood cells and their contents, the degradation of proteins and the transformation of ammoniacal nitrogen. in nitrates. At this stage, a mineralization of the fat fraction and the carbon portion of the proteins is obtained, the amino functions of the proteins being transformed into ammoniacal nitrogen and then nitrates. The second cocktail will then be used to remove nitrogen in gaseous form.

According to a preferred characteristic of the composition which is the subject of the invention, the first cocktail comprises i) at least one lipolytic bacterial strain belonging to the genus Klebsiella or Myroides, ii) at least one hemolytic bacterial strain belonging to the genus Aeromonas or Proteus, and iii) at least one nitrifying bacterial strain belonging to the genus Citrobacter, Acinobacter, Proteus, or Stenotrophomonas. In a concern of reliability and durability of the treatment, it is proposed that each biological function be doubled, so that if a bacterial population was to wither for one reason or another, for example because of the presence of other competitive microorganisms or because of certain toxicities of the effluents, the other bacterial population having the same function continues to provide the treatment. Therefore, advantageously, the first cocktail comprises i) at least two lipolytic bacterial strains belonging to the genera Klebsiella or Myroides, ii) at least two hemolytic bacterial strains belonging to the genera Aeromonas or Proteus, and iii) at least two strains. nitrifying bacterial belonging to the genera Citrobacter, Acinobacter, Proteus, or Stenotrophomonas.

According to a particularly interesting variant embodiment of the invention, the first cocktail comprises: i) at least two bacterial strains belonging to the species: Klebsiella oxytoca, Myroides odoratus, ii) at least two bacterial strains belonging to the species Aeromonas veroni bv., Proteus mirabilis, and iii) at least two bacterial strains belonging to the species Citrobacter freundii, Acinobacter haemolyticus, Proteus vulgaris, Stenotrophomonas maltophilia.

According to another preferred feature of the composition which is the subject of the invention, the second cocktail comprises at least one denitrifying bacterial strain belonging to the genus Pseudomonas or Stenotrophomonas.

Advantageously, said second cocktail comprises at least two bacterial strains belonging to the species Pseudomonas fluorescens, Pseudomonas nitroreducens, Pseudomonas aeruginosa, Stenotrophomonas maltophilia. The bacterial composition according to the invention is particularly suitable for being used in a treatment method, which is also the subject of the invention. This method of treating fat effluents containing blood essentially comprises the steps of:

- culturing in a first and a second biological reactors, respectively a first and a second bacterial cocktails of the composition according to the invention as described above,

- Introduce the effluent to be treated in a stirred homogenization tank, - Circulate the homogenized effluent in the first reactor to degrade fats and blood cells, digest the blood proteins and perform the nitrification reactions,

circulating the effluent from the first reactor in the second reactor to achieve denitrification of nitrates to the nitrogen gas,

- Evacuate the effluent thus treated from the second reactor to a refiner, before rejecting it to a municipal wastewater treatment plant.

This method of treating blood-containing fatty effluents can be qualified as a pre-treatment process insofar as it is intended to reduce the levels of COD, total nitrogen and MES of the wastewater to levels allowing their management by means of conventional treatments in STEP. It is remarkable by the implementation of two associated bacterial cocktails, the complementary activities of which ensure a thorough degradation of the fat and blood fractions which until now had to be treated separately and by several processes.

According to an advantageous characteristic of the method which is the subject of the present invention, the first bioreactor contains the first cocktail in free culture, subjected to aeration and permanent stirring, performing aerobic conditions. According to another advantageous characteristic of the method which is the subject of the invention, the second bioreactor contains the second cocktail in a support culture, under anoxic conditions. The culture support may be chosen from the supports known to those skilled in the art, such as mineral supports based on zeolite or pozzolan. In practice, the microorganisms according to the invention are advantageously added in freeze-dried form.

Advantageously, the reactors are dimensioned so that the hydraulic residence time TSH1 in the first reactor and the hydraulic residence time TSH2 in the second reactor are in a ratio TSH1 / TSH2 ranging from 2 to 3. In other words the process is preferably carried out on a treatment plant whose first reactor contains a volume of liquor V1 two to three times higher than the volume V2 of liquor present in the second reactor.

According to another advantageous characteristic of the claimed process, the effluent from the first or second bioreactor may be partly returned to the homogenization vessel by activation of a recirculation circuit, to undergo a new treatment cycle, complete or partial.

Preferably, according to the invention, the effluent from the second bioreactor is half returned to the homogenization tank by activation of a recirculation circuit. It is thus subjected to a new complete cycle of treatment. According to a preferred characteristic of the process which is the subject of the invention, suspended solids larger than 1 mm are removed on the incoming effluent by means of a screen placed at the inlet of the homogenizer.

The bacterial composition according to the invention as it has just been described finds an application in the treatment of fat effluents containing blood from the food and agro-food industries. It is particularly suitable for the treatment of wastewater from the slaughter of animals by the process described above.

The process according to the invention and the associated use of the two bacterial cocktails allows on-site disposal with performances greater than 80% in terms of fat reduction, 60% in terms of COD abatement and 60% in terms of reduction of COD. terms of abatement of total nitrogen. Its implementation generates little or no sludge and therefore limits the sector requiring transport by truck and disposal thereof. It is now possible to directly evacuate these complex effluents to the municipal network in compliance with the discharge standards as defined by Article 28 of the Decree of 30 April 2004: COD below 2000 mg / l, MEST below 600 mg / l, total nitrogen less than 150 mg / l.

The invention thus allows a reduction on COD, greases, suspended solids and total nitrogen, which constitutes an effective and economical pre-treatment of the effluents directly on the industrial site which generates them. The present invention will be better understood, and details will arise, in the light of the description which will be made of different embodiments, in relation to Figure 1 attached, schematically showing a treatment plant by the method according to the invention. invention.

EXAMPLE 1 - Bacterial Composition

In this example, a bacterial composition is presented comprising, for each desired function, two strains capable of ensuring each of them, intended to seed a first reactor R1 and a second reactor R2.

Seeding of R1:

- hemolytic strains: AV1 = Aeromonas veronii bv .; PM1 = Proteus mirabilis, for each strain: 0.8 g of freeze-dried microorganisms / kg of total nitrogen;

lipase strains: K01 = Klebsiella oxytoca; M01 = Myroides odoratus, for each strain: 0.014 g of freeze-dried microorganisms / kg of COD;

- nitrifying strains: CF1 = Citrobacter freundii; AH1 = Acinetobacter haemolyticus, for each strain: 0.8 g of freeze-dried microorganisms / kg of total nitrogen; Seeding R2:

denitrifying strains: PF1 = Pseudomonas fluorescens; PN1 = Pseudomonas nitroreducens, for each strain: 0.8 g lyophilized pure microorganisms / kg total nitrogen; EXAMPLE 2 - Implementation

FIG. 1 shows an installation for the treatment of fatty effluents containing blood according to the method of the invention. It consists mainly of: - the homogenization tank 3 capable of receiving the effluent to be treated by the feed 7,

the first biological reactor 1 operating under an aerobic regime,

the second biological reactor 2 containing the bacterial culture support 5, this reactor operating under anoxic regime,

- the refiner 4 with exhaust outlet 8.

Pumping means (conduits and pumps) 9, 9 ', 9 "ensure the circulation of the effluent through the homogenization tank 3, the reactors 1, 2 and the refiner 4, in this order. 3 is equipped at the inlet of the screen 10, for example a rotary sieve screen, whose mesh of 1 mm makes it possible to eliminate the suspended matter and is agitated continuously. free culture bacteria cocktail It is aerated and stirred continuously, for example by means of a compressor The second reactor 2 contains the second bacterial cocktail in culture on support It is neither agitated nor aerated The bacterial carrier, occupying half of its total volume, is a zeolite (type Chabamim ™, diameter 0.5 mm) .This reactor is fed from below to allow the diffusion of the effluent through the bacterial support, in anoxic conditions, the tanks are preferably of cylindrical, HDPE (high density polyethylene), stainless steel or concrete.

The plant is also provided with the recirculation circuit 6 of the effluent from the second reactor 2 to the homogenization tank 3, with the pump 9 "'.

The installation may advantageously also include one or more of the following means, not shown in FIG. 1, but known to a person skilled in the art who knows how to choose, make and use them:

a recirculation circuit of the effluent from the first reactor to the homogenization tank, with recirculation pump,

a circuit for recirculating the effluent from the second reactor 2 to the first reactor 1, with recirculation pump,

means for controlling the physico-chemical parameters (pH, redox, temperature probes, etc.), automatic control means and monitoring of the installation,

- a power supply.

The operation of the above installation according to the inventive method is for example the following. The homogenization tank 3 is fed with the effluent to be pretreated as it is produced. The homogenization tank 3 is stirred continuously. The suspended solids (MES) larger than 1 mm are removed using the screen 10 placed at the inlet of the homogenizer 3. From the homogenizer 3, the first biological reactor 1 is fed with stirring. and aerated, which contains a free culture of the first cocktail of bacteria as described in Example 1. At this level, occur reactions of hydrolysis and β-oxidation of fats (mineralization), degradation of blood cells, blood protein digestion, as well as nitrification reactions.

From the first biological reactor 1, the second biological reactor 2, filled with a mineral bacterial carrier of zeolite or pozzolan type (at a rate of 7.5 kg / kg COD / day, +/- 15%), is fed, operating in anoxia. The nitrates generated in the first reactor 1 are converted into a dinitrogen gas by a denitrification reaction.

According to the method described here, the recirculation circuit between the second reactor 2 and the homogenizer 3 operates continuously, with a recirculation rate of 50%. The treated effluent is discharged to the refiner 4, before being discharged to the treatment plant for the final conventional treatment.

The average residence time of the effluents in the plant according to the invention is of the order of 30 hours, of which 20 hours in the aerobic bioreactor R1, and 10 hours in the anaerobic bioreactor R2. The useful volumes of vat room (corresponding to the volumes of effluent) are in general:

- Flight. reactor R1 = Vol. 24h production / (24 / TSH reactor R1)

- Reactor flight R2 = ½ x Vol. reactor R1

- Flight. homogenizer = 2 x (reactor volume R1 + reactor volume R2)

- Flight. refiner = ½ x Vol. reactor R1 With all the parameters set here, the treatment was conducted for several months successfully, without sludge formation in the refiner.

The purification rates obtained under the conditions described above, the reactors being inoculated with the composition of Example 1, are reported in Table 1. The treated effluents come from the abattoir Regional Municipal d'Ales (multi-slaughterhouse - species). The abatement is given as a percentage (% slaughter). The chemical oxygen demand, initial and final (DCOi, DCOf, expressed in mg / l) was measured by spectrophotometry (acid dichromate oxidation) using Spectroquant (Merck) type measuring kits. The total nitrogen (early N, in mg / l) was determined by spectrophotometry (acid digestion, Koroleff method) using Spectroquant (Merck) type measuring kits. The hexane extractable materials (MEH, in mg / l) were assayed by hexane extraction (NFT 90,202). The suspended solids (MES, in mg / l) were measured by the filtration method defined by the NFT 90 105 standard.

TABLE 1

The decrease in COD indicates the elimination of the oxidizable organic material represented mainly by the fats in the effluents of slaughterhouse. The treatment output COD is less than 2000 mg / l with allowances greater than 50% and up to 85%. Fats expressed by the term MEH are eliminated in this case to more than 95%. The total nitrogen contained essentially in the blood proteins is eliminated at 60% on average, to go down to concentrations lower or equal to 150 mg / l. The suspended solids at the outlet are less than 600 mg / l.

EXAMPLE 3 - Efficacy tests on strains

The results of biodegradation tests on organic matter and nitrogen compounds by selected strains according to the invention are presented here on effluents from different slaughterhouses (poultry, beef, multi-species). Two sets of measurements were performed for each parameter (see Tables 2a and 2b). The measurements of COD and total nitrogen were carried out according to the methods already indicated.

1) - Real Effluent Sterilized - Poultry Slaughterhouse

Culture conditions: aerobic, in vial by filtration 0.2 μηη - 30 ° C - agitation 150 rpm. AV1 = Aeromonas veronii bv., PM1 = Proteus mirabilis (haemolytic strains)

K01 = Klebsiella oxytoca, M01 = Myroides odoratus (lipolytic strains)

TABLES 2a and 2b (repetitions)

The strains tested show a high efficiency on the reduction of the COD, when they are alone as in the form of cocktail. COD abatements are greater than 86% pure culture and consortium. The association of bacteria does not decrease the effectiveness of the degradation of organic compounds. There is a positive effect of haemolytic strains on the reduction of COD. The combination of haemolytic strains with lipolytic strains makes it possible to maintain an effectiveness of the degradation of organic compounds (and thus a good reduction of COD). 2) - Sterilized real effluents - Multi-species slaughterhouse

Culture conditions: aerobic, in vial by filtration 0.2 μηη - 30 ° C - agitation 150 rpm. Same strains as above. The COD measurements were carried out according to the methods already indicated. The results are shown in Tables 3a and 3b. The results obtained for effluents from multi-species slaughterhouses are at the same level, or better, than those obtained for effluents from a poultry slaughterhouse.

TABLES 3a and 3b

3) - Unsterilized real effluent - Poultry and beef slaughterhouse

Culture conditions: aerobic, stirred bioreactor 200 rpm, aerated: 80% 0 ₂ , 20 °.

The strains are the same as above. The COD measurements were carried out according to the methods already indicated. The results are shown in Table 4.

TABLE 4

The selected strains confirm their satisfactory behavior on unsterilized effluents from different types of slaughterhouses.

4) Unsterilized real effluent - Poultry, beef and multi-species slaughterhouses The effluents having undergone the first stage of the aerobic bioreactor treatment as indicated above were then subjected to the following test: the effluent is treated under aerobic conditions by a cocktail of 4 nitrifying strains, then under anoxic conditions by a cocktail of denitrifying strains, fixed by circulation of a zeolite column loop culture during the 24 hours preceding the treatment of the effluent, at 20 ° C., TSH 7h.

- Cocktail of 4 nitrifying strains:

CF1 = Citrobacter freundii PV1 = Proteus vulgaris

AH1 = Acinetobacter haemolyticus SM1 = Stenotrophomonas maltophilia

- Cocktail of 3 denitrifying strains:

PA1 = Pseudomonas aeruginosa PF1 = Pseudomonas fluorescens

SM2 = Stenotrophomonas maltophilia Four effluents from four different slaughterhouses were treated according to this scheme, with recirculation on the inoculated zeolite column. The results obtained are summarized in Table 5.

TABLE 5

A reduction of more than 44% of the total nitrogen initially present in the effluents is observed. It is also noted that the efficiency is equivalent for the various effluents with a maximum of 60% reduction for an effluent from a multi-species slaughterhouse.

EXAMPLE 4 - Efficiency Tests on the Process

Pilot tests have been carried out for different modes of implementation of the process according to the invention, in order to optimize the treatment conditions to be applied to an effluent. given. The parameters tested are the hydraulic residence time (TSH, expressed in hours) in the reactors R1 and R2, and different recirculation configurations between the reactors R1, R2 and the homogenizer H. The total COD and nitrogen measurements were carried out according to the methods already indicated.

Two compositions of microorganisms were tested:

^■ Inoculation of type (a): the R1 and R2 reactors were inoculated with the cocktails of Example 1.

^■ Inoculation of type (b): the R1 and R2 reactors were inoculated with cocktails composed of the same strains, with doubled proportions for the nitrifying and denitrifying activities, namely:

- Inoculation of R1:

- haemolytic strains: AV1 + PM1, for each strain: 0.8 g of freeze-dried microorganisms / kg of total nitrogen;

lipase strains: K01 + M01, for each strain: 0.014 g of freeze-dried pure microorganisms / kg of COD;

nitrifying strains: CF1 + AH1, for each strain: 1.6 g of freeze-dried microorganisms / kg of total nitrogen;

- Inoculation of R2:

denitrifying strains: PF1 + PN1, for each strain: 1.6 g of freeze-dried microorganisms / kg of total nitrogen;

The recirculation configurations adopted and the results obtained are presented in Table 6. In view of these results, it appears that for the treated effluent, the configuration 4, in which no recirculation is provided, provides good results on the COD, but too much nitrogen variability with value overruns, at least compared to the discharge standards in force. This configuration will therefore make it necessary to use several cycles of treatment to achieve a satisfactory result.

In configuration 1, the results are correct in COD and Nitrogen, but no more. The residence time is sufficient to treat the COD.

In configuration 3, nitrogen and COD exceed the desired levels. The residence time is too short. In addition, its implementation is technically more complicated than the other provisions. It will not be retained here, except in special cases.

TABLE 6

The optimum embodiment of the invention is found with the configuration 2 under the following conditions: recirculation of the reactor R2 to the homogenizer at a level of 50%, with TSH in R1 = 20 hours and TSH in R2 = 8 hours.

In this configuration, however, a nitrogen exceedance (greater than 150 mg / l) is observed when the microorganisms are in the inoculation conditions (a), whereas with the seeding (b), good results are obtained in COD. as in nitrogen (see Table 6, values in bold). This configuration will be preferred over other configurations tested.

Claims

1. Bacterial composition for the treatment of fatty effluents containing blood, characterized in that it consists of:

a second cocktail comprising at least one bacterial strain with denitrifying activity.

2. - Composition according to claim 1, characterized in that the first cocktail comprises i) at least one lipolytic bacterial strain belonging to the genus Klebsiella or Myroides, ii) at least one hemolytic bacterial strain belonging to the genus Aeromonas or Proteus, and iii) at least one nitrifying bacterial strain belonging to the genus Citrobacter, Acinobacter, Proteus, or Stenotrophomonas.

3. - Composition according to claim 1 or 2, characterized in that the first cocktail comprises i) at least two lipolytic bacterial strains belonging to the genera Klebsiella or Myroides, ii) at least two hemolytic bacterial strains belonging to the genera Aeromonas or Proteus, and iii) at least two nitrifying bacterial strains belonging to the genera Citrobacter, Acinobacter, Proteus, or Stenotrophomonas.

4.- composition according to one of the preceding claims, characterized in that the first cocktail comprises i) at least two bacterial strains belonging to the species: Klebsiella oxytoca, Myroides odoratus, ii) at least two bacterial strains belonging to the species Aeromonas veroni bv Proteus mirabilis, and iii) at least two bacterial strains belonging to the species Citrobacter freundii, Acinobacter haemolyticus, Proteus vulgaris, Stenotrophomonas maltophilia.

5. Composition according to one of the preceding claims, characterized in that the second cocktail comprises at least one bacterial denitrifying strain belonging to the genus Pseudomonas or Stenotrophomonas.

6. Composition according to one of the preceding claims, characterized in that the second cocktail comprises at least two bacterial strains belonging to the species Pseudomonas fluorescens, Pseudomonas nitroreducens, Pseudomonas aeruginosa, Stenotrophomonas maltophilia.

7 - Process for treating fatty effluents containing blood, characterized in that it essentially comprises the steps of:

- culturing in a first and a second biological reactors (1, 2), respectively a first and a second bacterial cocktails of the composition according to one of claims 1 to 6,

introducing the effluent to be treated into a homogenization tank (3) kept under stirring,

circulating the homogenized effluent in the first reactor (1) to degrade the fats and to degrade the blood cells, to digest the proteins of the blood and to carry out the nitrification reactions,

circulating the effluent from the first reactor (1) in the second reactor (2) to denitrify the nitrates with nitrogen gas,

- Evacuate the effluent thus treated from the second reactor (2) to a refiner (4), before rejecting it to a treatment plant.

8. A process according to claim 7, characterized in that the first reactor (1) contains the first cocktail in free culture, subjected to aeration and permanent stirring performing aerobic conditions.

9. A process according to claim 7 or 8, characterized in that the second reactor (2) contains the second cocktail in a support culture (5) under anoxic conditions.

10. - Method according to one of claims 7 to 9, characterized in that the reactors (1, 2) are dimensioned so that the hydraulic residence time TSH1 in said first reactor and the hydraulic residence time TSH2 in said second reactor are in a ratio TSH1 / TSH2 ranging from 2 to 3.

1 1. - Method according to one of claims 7 to 10, characterized in that the effluent from the first or second bioreactor (1, 2) is partly returned to the homogenization tank (3) by activation of a circuit recirculation (6)

12.- Method according to the preceding claim, characterized in that the effluent from the second bioreactor (2) is half returned to the homogenization tank (3) by activation of a recirculation circuit (6).

13.- Method according to one of claims 7 to 12, characterized in that the suspended materials larger than 1 mm are removed using a screen placed at the inlet of the homogenizer (3) .

14.- Application of a bacterial composition according to one of claims 1 to 6 for the treatment of fatty effluents containing blood from the food and agri-food industries.