EP2242592A2

EP2242592A2 - Process and equipment for the oxidation of organic matter

Info

Publication number: EP2242592A2
Application number: EP09709850A
Authority: EP
Inventors: Alain Bergel; Luc Etcheverry; Benjamin Erable
Original assignee: Centre National de la Recherche Scientifique CNRS; Institut National Polytechnique de Toulouse INPT
Current assignee: Centre National de la Recherche Scientifique CNRS; Institut National Polytechnique de Toulouse INPT
Priority date: 2008-02-11
Filing date: 2009-02-11
Publication date: 2010-10-27
Also published as: FR2927326B1; WO2009101358A3; US20110042235A1; FR2927326A1; WO2009101358A2

Abstract

The present invention relates to a process for the oxidation of organic matter and the kit for the implementation thereof, especially for the treatment of waste, effluents and biosolids.

Description

PROCESS AND EQUIPMENT FOR OXIDATION OF ORGANIC MATERIALS

Waste production in France exceeds 600 million tonnes per year. More than two-thirds are organic waste. They have the following origins: - agricultural waste (animal waste, crop waste and forest waste): 84% of the total quantity of organic waste;

- waste from agro-food industries: 10%;

- community waste (sewage sludge, septic tank sludge, green spaces, markets, street cleaning): 5%; - household waste (garbage): 1%.

In France, 95% of agglomerations with more than 10,000 population equivalents have a wastewater treatment plant. The production of sewage sludge is constantly increasing. Today, almost all wastewater treatment plants have biological treatment, in which microorganisms degrade the organic, nitrogen and phosphorus materials that constitute the polluting load of the wastewater. Most often, urban effluents are sent to a pool where these organisms proliferate in the form of activated sludge. To act, activated sludge consumes oxygen, so be sure to air properly. Aeration represents 60% to 80% of the energy expenditure of this type of treatment plant, which corresponds to a consumption of about 50 kWh / year / inhabitant equivalent. It is generally accepted that optimization of this station should result in savings of between 10% and 20% on the total cost of running the station.

In parallel with urban wastewater treatment plants, the current trend is to have mini-treatment plants at the outlet of the facilities that produce certain specific effluents, such as the treatment of the oil charges at the output of the mechanical manufacturing workshops. treatment of slurry or dairy effluents leaving livestock units or agro-food processing centers, detoxification of hospital effluents, etc. New needs are also developing, such as biological treatments of swimming pool water or domestic composting of food waste.

In any case, it is desirable to improve the oxidation of organic materials by microorganisms and oxygen.

Microorganisms spontaneously adhere to all types of surfaces and form films called biofilms consisting of said microorganisms, a matrix of exopolymeric substances (polysaccharides, proteins, macromolecules ...) they excrete, substances produced by microbial metabolism and accumulated compounds from the medium or from the degradation of the support surface. It has recently been discovered that biofilms grown on conductive surfaces are able to utilize these surfaces to evacuate electrons from their metabolism (DR Bond et al., Science 295 (2002) 483, and LM Tender et al., Nature Biotechnology 20

(2002) 821; H. J. Kim et al., Enzyme and Microbial Technology (2002) 145). The mechanisms are not yet fully deciphered, several reaction paths are evoked, depending on the type of microorganisms that make up the biofilms (K. Rabaey et al., Trends in Biotechnology 23 (2005) 291, DR Lovley, Current Opinion in Biotechnology 17 (2006) 1). In some cases, microorganisms produce small redox compounds that act as electrochemical mediators between microbial cells and the surface: these compounds are reduced by the microorganism and oxidize back to the surface. Other microorganisms have been shown to be able to directly transfer electrons from the oxidation of their metabolism to a conductive surface by means of redox compounds included in their outer membrane. Some microorganisms form conductive pili to electrochemically connect to surfaces or other microorganisms. Whatever the reaction paths, biofilms are able to oxidize organic materials by directly transferring electrons to a conductive surface. Other biofilms have been demonstrated capable of catalyzing the reduction of oxygen on materials such as stainless steels (A. Bergel et al., Electrochemistry Communications, 2005, 7, 900-904, FR 02 10009) which under their initial state devoid of biofilm, are not known to ensure high speeds of reduction of oxygen. These biofilms can be used on the surface intended to evacuate the electrons of the system to a dissolved compound, oxygen for example.

Whether they are capable of catalyzing electrochemical oxidation or reduction reactions, these biofilms will be referred to herein as electrochemically active biofilms or EA biofilms.

Nevertheless, these technologies have mainly been provided for batteries, that is, to produce electricity. This therefore requires the installation of a complex electrical circuit, not very compatible with facilities such as waste treatment units. Moreover, these batteries do not currently produce enough electricity to make this implementation attractive on waste facilities.

On the other hand, the waste installations are confronted with their high consumption of electricity necessary to feed the aerators. It is therefore desirable to design systems that reduce or even eliminate the need for aeration of waste or effluents to be treated. Indeed, it is known that the aeration of the media to be treated is necessary to allow the microorganisms to develop and thus consume the organic materials. Breathing consists of the removal of electrons from the microbial process of oxidation of organic matter to an external acceptor of electrons, most often dissolved oxygen in the medium, which is thus reduced to water. Some microorganisms are able to breathe by reducing other electron acceptors such as nitrates, nitrites or sulfates for example. The lack of electron acceptor in the medium, oxygen in this case, significantly reduces the ability of microorganisms to oxidize organic matter, or even annihilates it completely.

Thus, it is particularly desirable to provide a method for limiting or even reducing the use of aerators.

The present invention proposes to develop the microorganisms on conductive surfaces that are capable of collecting the electrons from the metabolic processes of oxidation of organic materials. These conductive surfaces on which the microorganisms develop, thus ensure the extraction of electrons.

To evacuate the electrons, the surface that supports the microorganisms that oxidize the organic matter must be connected with a surface that evacuates them towards the final acceptor, the oxygen for example. Thus, the two surfaces, the one that collects the electrons from the microorganisms that oxidize the organic matter, and the one that evacuates the electrons to the final acceptor of electrons, oxygen for example, allow the microorganisms to "breathe". The same principle can be used with nitrates, nitrites, sulphates, thiosulphates or any other dissolved or gaseous compound that can be reduced.

Thus, according to a first object, the present invention relates to a process for the oxidation of organic materials comprising the application to said organic materials to be treated of a system comprising: a first portion (1) of conductive material;

a second portion (2) of conductive material, said method comprising simultaneously:

contacting the first part (1) with said organic materials and one or more microorganisms (s) capable of forming an EA biofilm (4) on the surface of said first part, contacting said second portion with an electron acceptor in the presence of a catalyst (5) and / or one or more microorganisms capable of forming an EA biofilm (5 ') on the surface of said second part, and

- The electrical contact of said first and second parts by a short circuit.

Organic materials are any material that can be oxidized. These include agricultural waste (livestock waste, crop and forestry waste), agro-food waste, community waste (sewage sludge, septic tank sludge, green spaces, markets, street cleaning), household waste (garbage cans), etc.

According to a first embodiment, the system according to the invention can thus be formed by a single electrically conductive element, such as an electrically conductive bar whose one end provides the first part and the other end the second part.

According to another embodiment, the system according to the invention can also be formed of two distinct elements brought into electrical contact by a resistance conductor the lowest possible, in particular substantially zero, and in any case less than 10 ohms. The two elements may be formed of the same conductive material or two different conductive materials; they can be integral or interconnected by a single conductive element.

Thus, in the case of effluent treatment in an anoxic reactor, said system may comprise a first portion of graphite, immersed in the anaerobic layers of the reactor, part connected by a conductor to a second part made of stainless steel or any type of material capable of catalyzing the reduction of oxygen in the upper and aerated part of the reactor. To achieve the reducing zone of the system according to the invention, it is possible to use any type of cathode known in the state of the art, such as air cathodes for example in order to evacuate the electrons to oxygen gas. The second part may comprise a deposited catalyst such as platinum and / or an EA biofilm, formed for example according to the procedure described in the patent application FR 0210009, in order to catalyze the reduction reaction.

According to another embodiment, the system according to the invention can use conductive parts of the reactor, simply by making a short circuit between them. One can, for example, constitute a system according to the invention by connecting by a electrical conductor of substantially zero resistance the walls or lining of a waste or effluent treatment reactor, with an internal aeration module. In this case, the walls or lining would constitute the oxidizing part of the system according to the invention, the ventilation module consisting of a conductive material, for example steel, constituting the reducing part.

According to the invention, the first and second parts are at the same electrochemical potential.

Advantageously, said first and second portions are immersed in a single reactor containing said organic materials to be treated, said microorganisms capable of forming an EA film, the electron acceptor, said reactor not comprising a separating element, such as a membrane, between said first and second parts.

The electron acceptor may be selected from any substance capable of being reduced. It can be favorably selected from oxygen, nitrates, nitrites, sulfates, thiosulfate, more preferably oxygen. The reduction of the electron acceptor, especially when it comes to oxygen, can occur spontaneously on certain materials such as graphite or steels, for example. However, it may be advantageous to use a reduction catalyst of said electron acceptor, either a known compound deposited on its surface, or a microbial biofilm, or a combination of both. Said catalyst is chosen from any substance capable of catalyzing the reduction reaction. It may especially be metal such as platinum or a compound based on platinum, nickel or silver, for example. These compounds are deposited on the surface of the second part by any method known to those skilled in the art, such as electrochemical deposition, CVD deposition (Chemical Vapor Deposition), sol-gel type deposits, trapping. in polymer films, paints, inks, etc. The catalysis can also be carried out by a biofilm consisting of microorganisms capable of forming an efficient EA biofilm for said electron acceptor. In this case the microbial biofilm may form spontaneously on the surface of the second part, or a pretreatment may cause, initiate or accelerate its formation, for example as described in the patent (FR0210009). The said microorganism (s) forming an EA biofilm (4, 5 ') on the surface of the first part and optionally the second part of the system according to the invention exist (s) generally spontaneously in the reaction mixture. treat. Alternatively or cumulatively, it is possible to seed the reaction mixture to be treated with suitable microorganisms in all possible forms (inocula, culture broths, lyophilizates, etc.). For this purpose, samples of media known to contain microorganisms readily EA biofilms, such as aqueous effluent sludge (eg sewage treatment plants) sediments or marine biofilms, composts and any other medium known to those skilled in the art to give EA biofilms. It may be advantageous to seed with samples of EA biofilms previously collected on anodes (for the first part) or cathodes (for the second part) of any system using EA biofilms, such as the present device or batteries. microbial fuel for example. It is indeed known that EA biofilms are good inocula for reforming EA biofilms. The first subcultures often provide a significant increase in catalytic activity. It is also possible to use pure cultures of microorganisms known for their ability to form EA biofilms, such as Geobacter, Desulfuromonas, Shewanella, Geopsychrobacter, Rhodoferrax, Geothrix, etc. and any EA strain known in the state of the art.

The seeding can be done at the beginning of the start-up of the device, it can also possibly be renewed during operation to reactivate the device, for example to mitigate a decrease in its effectiveness or after an operating incident.

The conducting materials of the first and second parts (1), (2), which may be identical or different, may be chosen from any conductive material, such as in particular graphites, carbons, metallic materials such as stainless steels or the materials usually used for the electrodes. such as, for example, tantalum iridium oxides deposited on titanium. In particular, graphite and stainless steel are preferred.

The person skilled in the art will choose the material according to the type of medium to be treated and the type of microorganisms which will appear to him the most appropriate for treating these environments. It is known that graphites, carbons, metallic materials, such as stainless steels or materials specifically designed to serve as electrodes, such as tantalum iridium oxides deposited on titanium (electrode technology called DSA), allow adequate development of EA biofilms. The known materials suitable for EA biofilms being extremely diverse, any type of conductive material may be suitable, depending on the composition of the medium to be treated and the type of microorganisms present.

Advantageously, the materials of the first and second parts (1), (2) can be pretreated in bulk or on the surface, so as to optimize both their ability to adhere the EA biofilm, their electronic conductivity and their ability to promote the development of strongly EA biofilms. It is known that increased roughness promotes the development of effective EA biofilms. Any modification of the morphology surface: grooving, sanding, micro- and nanostructuring, etc. which will have the effect of increasing the area available for microbial adhesion and promoting this membership, will also be favorable to the system.

The system according to the invention may advantageously be implemented with a single element, for example a bar of conductive material, thus realizing the short-circuit in the two parts of its surface, namely on the one hand, that ensuring the oxidation of organic matter catalyzed by a biofilm EA and, on the other hand, that ensuring the reduction of a dissolved or gaseous electron acceptor species. Any other form that will be adapted to the configuration of the medium to be treated may also be considered, since each of the two parts respectively providing the oxidation and reduction are short-circuited.

Advantageously, the shape and structure of the system according to the invention can be designed to create the largest possible exchange surfaces for each of the functional areas. These include porous structures, such as foams or felts, and any type of structure with a large specific surface area or a high degree of vacuum known in the state of the art. Similarly, the shapes of the propeller type, brushes, dendrites, grids, etc. which increase the area of each element for a given volume may be favorable to its effectiveness. The shape can also be designed in correlation with the hydrodynamics of the medium for circulating or agitated liquid environments.

The process according to the invention can generally be carried out for the time necessary for the oxidation. Thus, if the oxidation has to be carried out continuously, the process can also operate continuously. If, on the other hand, the oxidation has to be stopped, the process can be interrupted, for example by activating a switch located between the first and second parts or by removing the system according to the invention from the organic materials to be treated.

The system according to the invention is advantageously placed in the waste or effluent treatment reactor so as to ensure a different reaction on each of its two parts. Thus, the first part is advantageously placed in the treatment reactor so as to ensure on its surface the oxidation process of the organic material catalyzed by a biofilm EA. Simultaneously, the second part must ensure the reduction reaction (s) of a species contained in a portion of the reactor, dissolved or gaseous oxygen for example. Thus, the system according to the invention can simply be immersed vertically in an anoxic reactor so that that the oxidation of the organic matter takes place on its surface on the part immersed deeper in the reactor, rich in organic matter, whereas the reduction of the oxygen takes place on the surface of the second part, placed in the zone minus submerged reactor, richer in oxygen, such as the surface area. Thus, the reactor can be configured to promote the establishment of an area richer in organic matter to be treated and a richer zone of electron acceptor (oxygen, nitrates, etc.).

This can be achieved in particular by: simple sedimentation in a conventional reactor, the organic materials sedimenting in the lower part of the reactor; aerating preferentially only a portion of the reactor, or by supplying only a portion of the electron acceptor reactor (nitrates, oxygen, etc.); defining a reactor configuration favorable to the establishment of these two zones, for example using two tanks coupled in series; and / or by any combination of these techniques and any other technique known to those skilled in the art which makes it possible to define preferential zones.

The system according to the invention being composed of two parts, possibly identical or integral, providing different functions, it may be advantageous to optimize these two parts independently to make them as efficient as possible. Preferably, the system according to the invention may have a first portion optimized to ensure the adhesion of EA biofilms that oxidize the organic material and a second optimized portion to ensure the evacuation of electrons to a dissolved acceptor compound, oxygen for example this reaction being catalyzed by an EA biofilm or a catalyst such as platinum.

The optimization includes the definition of the shape, the location with respect to the reactor, the material and / or the surface coating, the surface morphology, the presence of a catalyst and any other parameter known in the state of the art. the art can improve the two targeted reactions.

Thus, the system according to the invention can be added to an existing reactor, or can use the parts of a reactor to form a system according to the invention, or modify the existing parts (shape, material, coating, etc.) for to make the effect of the system according to the invention more efficient. The method according to the invention may also comprise the prior application of a potential or a current to the system, in order to promote the initial development of the system according to the invention. This preliminary step can be performed for the time necessary for the system to operate independently, for example from a few hours to a few days. This step may be carried out in the same treatment reactor or independently in a reactor and a medium specially designed for this purpose.

In the case of batch treatment, it may be advantageous to start the process according to the invention by seeding the medium with microorganisms or complex inocula known in the state of the art to form the EA biofilms that are judged appropriate depending on the medium to be treated. Seeding can also be designed in an open environment as a start-up technique of the process according to the invention.

In its simplest embodiments, the process according to the invention does not require any modification of the reactors used in traditional waste and effluent treatment technologies. It suffices to add the system according to the invention within the existing equipment. However, it is not excluded to also modify the existing equipment to implement the principle of the invention on their very surface.

The system according to the invention is very flexible since it uses as reaction catalysts EA biofilms which form spontaneously from the media to be treated. These EA biofilms are able to adapt to variations in the quality and composition of the media to be treated.

In its simplest embodiments, the system according to the invention comprises a priori no moving part, no electrical equipment; it is robust and requires virtually no special maintenance. The system according to the invention can adapt to all types of waste and effluents; liquid effluents, but also solid waste, such as composting. It is sufficient, for it to be effective, to ensure sufficient contact between the medium to be treated and the surfaces of the system.

Unlike microbial fuel cells that could be implemented to intensify effluent treatment processes, the system proposed in the present invention does not divert any energy to produce electricity, thereby ensuring maximum efficiency for the treatment of wastewater. waste or effluent.

Thus, more particularly, the system according to the invention does not include a source of electrical energy, such as a source of voltage or current. Moreover, the system according to the invention is also distinguished from batteries in that it does not provide electricity. Thus, the device according to the invention does not include any electric charge and does not require the use of electrochemical reactors having a membrane or any other type of separator to delimit an anode compartment and a cathode compartment. Unlike a battery, the device described by the invention works best when all its parts have the same electrochemical potential.

According to another object, the present invention also relates to a kit for implementing the method according to the invention, said kit comprising: - a first portion (1) of conductive material;

- a second portion (2) of conductive material;

one or more microorganisms (4), (5 ') forming a film EA on the surface (s) of the first and possibly second parts; and

- means for short-circuiting (3) the first and second parts. According to a particular embodiment, the kit according to the invention does not include a membrane, a source of electrical energy, such as a voltage or current source, or electric charge.

Preferably, the kit according to the invention consists of said elements above. The first and second parts as well as the microorganism (s) and short circuiting means are defined as above.

Advantageously, the kit is suitable for immersion in a single reactor containing said organic materials to be treated, said microorganisms capable of forming an EA film, the electron acceptor; it does not include a separating element, such as a membrane.

The means of short-circuiting can in particular be chosen from any conductive element, of the lowest resistance possible, in particular substantially zero, and in any case less than 10 ohms.

The kit according to the invention may also comprise any element, instrument or compound usually used, making it possible to improve the implementation of the method, useful in particular for the pretreatment of the device, a possible seeding, monitoring of the system, its maintenance and its piloting. The pretreatment may comprise a polarization phase carried out in potentiostatic or intentiostatic mode either with the aid of a traditional electrochemical apparatus, or by galvanic coupling with a submerged electrode known to ensure a constant potential, such as zinc or alloy electrodes magnesium for example. These instruments are part of the kit. The seeding may be carried out by pure strains, or more effectively by consortia of microorganisms taken from EA biofilms, for example specifically cultivated for this purpose. These inocula of EA biofilms are part of the kit. The maintenance may consist of reproducing the preprocessing phases at predefined time intervals or when a decrease in the efficiency of the device is detected. The monitoring may be carried out in particular by measuring the potential of the device relative to a reference electrode forming part of the kit. The control can consist in supplying a voltage or a current intensity as described above, with the instruments (potentiostat, current generator, galvanic coupling ...) forming part of the kit.

figures

FIG. 1 represents a particular embodiment in which the system is formed of a single element, a bar for example, one end of which represents the first part (1) and the other end of which represents the second part (2). , the interface between the two parts constituting the short circuit (3). On the surface of the first part is formed an EA biofilm (4), while on the surface of the second part (2) is deposited a catalyst (5) and / or an EA biofilm (5 ') is formed. The system is immersed in the effluents to be treated (6) contained in a reactor (7).

FIG. 2 shows a variant according to which the system consists of two elements, two bars for example, the lower bar representing the first part (1) and the upper bar representing the second part (2), connected to each other by a driver ( 3). On the surface of the first part is formed an EA biofilm (4), while on the surface of the second part (2) is deposited a catalyst (5) and / or an EA biofilm (5 ') is formed. The system is immersed in the effluents to be treated (6) contained in a reactor (7).

The following example is given by way of non-limiting illustration of the present invention. Three identical bioreactors consist of glass tubes 60 mm in diameter and contain 500 ml of seawater. In order to promote rapid microbial growth, the three reactors are inoculated with the same microbial consortium collected by scraping a submerged surface at sea. In order to simulate the presence of a large organic load, successive additions of known amounts of sodium acetate are carried out simultaneously in each of the three reactors. The system according to the invention consists of a 50 cm ² graphite felt surface connected by a 30 cm titanium rod to a 5 cm ² platinum grid which constitutes the upper portion. Graphite is known to promote the formation of EA biofilms in marine environments, platinum wire is chosen to maximize the electrochemical reduction rates of dissolved oxygen. The system according to the invention is placed vertically in the reactor the platinum zone at the top, in the part that is assumed to be the most aerated of the reactors.

- Bioreactor A is the control bioreactor. It allows to follow the natural consumption of the acetate by the flora introduced in the medium.

The system according to the invention is introduced into the bioreactor B.

- Bioreactor C is equipped with the same system according to the invention with electrochemical assistance. In this case, the potentiostatic type of assistance is carried out using a potentiostat which imposes a fixed potential of -0.1V / ECS (saturated calomel reference electrode) to the oxidizing part of the system according to the invention. (anode).

This case simulates, for example, a pre-treatment phase of the device with electrochemical assistance.

Sodium acetate is added simultaneously to each bioreactor at a final concentration of 1 g / L. Several successive additions of acetate were made after complete disappearance of the initial charge.

The consumption of acetate is monitored in each reactor by taking 1 ml of sample and measured by an enzymatic assay (Boehringer-Mannheim kit, R-

Bioharm). The abatement is expressed in% of the load of each successive addition (1 g / L). Identical additions of acetate are made on days 0 (beginning of the experiment), 5,

10, 15, 20 simultaneously in the three bioreactors. The acetate measurements made before the new additions on days 5, 10 and 15 indicate a 100% abatement (total acetate consumption) in the three bioreactors. The average acetate abatement rate is around 0.2 g / L / day (ie 5 days to consume the 1 g / L added).

Significant differences appear from the ^4th adding acetate (day 15). The fifth addition is carried out on day 20, the measurements are performed day 18 and 19 (or 3 and 4 days after the ^4th addition) and days 23 and 24 (or 3 and 4 days after the ^5th addition). The acetate abatement rates reported in the table below indicate that:

the control reactor only manages to consume approximately 50% of the added acetate after 3 days; during the same period, the system according to the invention provides 61% abatement after the ^4th addition and 71% after the ^5th addition. These two results indicate that the system according to the invention is being put into operation, the performance of which improves over time. additions of acetate, certainly due to the progressive formation of EA biofilm on the oxidizing part of the system according to the invention.

- The system according to the invention assisted by electrochemistry retains a reduction rate identical to that of the start (0.2 g / L / day). In this case, the electrochemical assistance forces a faster formation of the EA biofilm, which may constitute a pretreatment procedure of the device. This makes it possible to evaluate the progress capability of the system according to the invention.

C - TE attends by

A - control B - potential TE imposed

^4th addition (day 15)

Day 18 52% 61% 79%

Day 19 71% 93% 99%

^5th added (day 20)

Day 23 51% 71% 80%

Day 24 65% 83% 89%

Claims

1. - Process for the oxidation of organic materials comprising the application to said organic materials to be treated of a system comprising: a first portion (1) of conductive material;

contacting the first part with said organic materials and one or more microorganisms (4) forming an electrochemically active biofilm (EA) on the surface of said first part,

contacting said second portion with an electron acceptor in the presence of a catalyst (5) and / or one or more microorganisms (5 ') forming an electrochemically active biofilm (EA) on the surface of said second part, and

- The electrical contact of said first and second parts by a short circuit.

2. - Method according to claim 1 such that said first and second parts form a same electrically conductive element.

3. - The method of claim 1 such that said first and second parts are distinct and short-circuited by an electrical conductor (3).

4. A process according to any preceding claim such that said electron acceptor selected from oxygen, nitrates, nitrites, sulfates, thiosulfate.

5. - Process according to any one of the preceding claims such that said catalyst (5) is deposited on the surface of said second part.

6. - Process according to any one of the preceding claims, such that the conductive materials of the first and second parts, identical or different, are chosen from graphites, carbons, metallic materials such as stainless steels or materials usually used for electrodes.

7. - Process according to any one of the preceding claims such that said (s) one or more microorganism (s) (5 ') form (s) an electrochemically active biofilm on the surface of the second part (2) ).

8. - Process according to any one of the preceding claims such that said (s) microorganism (s) (4) and optionally (5 ') exist (s) spontaneously in the reaction mixture to be treated.

9. A process according to any one of the preceding claims comprising the preliminary step of seeding the reaction mixture to be treated (6) by means of colonies of microorganism (s) appropriate.

10. - Method according to any one of the preceding claims such that said first and second parts (1), (2) are respectively constituted by the conductive parts of the reactor (7) in which the method is implemented.

11. - Method according to any one of the preceding claims wherein the system is applied so that the first part (1) is immersed in a zone of the reaction mixture (6) rich in microorganisms capable of forming an EA biofilm.

12. - Method according to any one of the preceding claims, such that the first part (1) and / or the second part (2) is (are) previously treated (s) so as to improve the adhesion and / or the development of the biofilm EA (4) and / or (5 ').

13. The method of claim 12 such that the pretreatment includes grooving, sanding, micro- or nanostructuring.

14. Kit for carrying out the method according to any one of the preceding claims, comprising:

- a first portion (1) of conductive material;

- a second portion (2) of conductive material;

one or more microorganisms capable of forming an EA biofilm; and

- means for short-circuiting (3) the first and second parts.

15. Kit according to claim 16, wherein said first part, second part, conducting material and / or microorganism are as defined according to any one of claims 1 to 13.