FR2924441A1 - Continuous bio-treatment of organic material of plant and/or animal origin to transform materials into biogas energy and compost, comprises e.g. aerobic hydrolysis of organic materials and acidogenesis and anaerobic acetogenesis of material - Google Patents

Abstract

Method for continuous bio-treatment of organic material of different plant and/or animal origin by using microorganisms for transforming the materials into biogas energy and compost, comprises (a) aerobic hydrolysis of organic materials, (b) acidogenesis and anaerobic acetogenesis of hydrolyzed organic material, (c) transformation of anaerobic methanogenesis by acidogenesis and acetogenesis, to produce the biogas, a concentrate and a liquid effluent, and (d) aerobic composting of the concentrate after solid/liquid separation.

Description

PROCESS FOR THE BIO-TREATMENT OF ORGANIC MATERIALS FOR THE PRODUCTION OF BIO-GAS AND COMPOST

FIELD OF THE INVENTION The invention relates to a process for bioprocessing organic materials for the purpose of producing bio-gas and compost from aerobic and anaerobic fermentations. STATE OF THE ART The production of compost by biotreatment processes of the aerobic type of organic material is normally carried out in open and ventilated windrows or in simple reactors. Such treatments are less complex and less expensive than anaerobic bio-treatments. However, anaerobic treatments are relatively more tolerant than aerobic treatments in the presence of foreign bodies in the organic material to be treated. However, because the process is comparatively slow, the anaerobic treatment requires a substantially greater volume of treatment of treated organic material when compared to aerobic treatments, and further such aerobic treatment does not lead to the production of energy. in the form of bio-gas.

Anaerobic bio-treatments of organic materials are, in turn, very effective in suppressing pathogenic germs and are, moreover, capable of producing energy in the form of biogas. These anaerobic biotreatments are relatively fast and are also less energy consuming when compared to the volume to be treated and when compared to aerobic treatments. However, olfactory nuisances inherent to anaerobic treatments require that such processes be conducted in closed buildings and in sealed reactors incorporating efficient odor treatment systems. Such technical sophistication leads to an expensive process, and in terms of installation, and in terms of operating cost.

Anaerobic treatment of organic materials in closed reactors is a proven technology applied to a wide variety of organic wastes such as animal slurry, liquid effluents and wastewater or effluents resulting from the processing of agro-food industries.

Typically, the technology is applied in an environment that can implement controlled industrial processes and where the organic material to be treated is available in a preferentially liquid form, sometimes also in solid form.

Several methods and technologies are available in the state of the art, for treating, under anaerobic conditions, organic materials; however, a too great heterogeneity of the organic material to be treated has the usual consequence of the unacceptable increase in the treatment costs and therefore in the production costs of the recoverable by-product, in particular biogas. In addition, the methane levels in the biogas produced are not as high as desired to then optimize the energy yields in the thermal generating units of electricity.

Obviously the current priorities of energy production from biomass, waste and more generally renewable materials, reinforce the interest of such approaches. This is why recent developments have sought to incorporate the advantages of economies of scale inherent in anaerobic degradation processes operating continuously with the possibilities of aerobic treatments. Thus, US 2005/0035058 discloses a method of treatment and a system, ie an installation for the continuous decomposition of organic materials first under anaerobic conditions and then under aerobic conditions for production purposes. bio-gas and compost. The installation comprises: a primary reactor defining at least two zones for the continuous reception of the organic material, one of said reactor zones being adapted to receive said organic material, while the other zone allows the collection of the organic material; decomposed organic matter recovered in the form of raw compost; drainage means for evacuating the organic leachate produced in the primary reactor; a secondary reactor for the anaerobic digestion of bio-treated organic leachate from the primary reactor and the production of biogas; Recirculation means for recycling the bio-treated organic leachate from the secondary reactor to the primary reactor; means for collecting biogas generated in the primary and secondary reactors; aeration means for aerobic decomposition of the organic material in the primary reactor; means for extracting the generated compost from the primary reactor, in order to release a reactor zone and thus to be able to receive another charge of organic matter.

The primary reactor is more precisely composed of a series of discrete zones, each adapted to be used for subsequent successive operations. organic matter loading, anaerobic decomposition of organic matter, aerobic decomposition of organic matter, and extraction of compost. The primary reactor is divided into contiguous zones, physical barriers separating the zones of the reactor from each other, these zones being able to be physically completely separated respectively in the clean structures.

The bioprocessing method for decomposing the organic matter to produce biogas and compost comprises the following successive stages: - the loading, in a dedicated zone of the primary reactor, of the organic matter, this primary reactor having at least two reaction zones for receiving the organic material by successive loading; decomposing the organic matter charge, under anaerobic conditions, for a predetermined period of time, in a zone of the reactor; aeration and aerobic treatment of organic matter, previously decomposed under anaerobic conditions, in the same reactor zone, to produce raw compost; the extraction of the raw compost from the reactor zone, in order to be able to prepare the loading of another charge of organic matter in the dedicated zone of the reactor.

The process uses a primary reactor having two reaction zones, one of the zones being charged with organic matter while the organic material decomposes in situ in the other zone of the reactor, this decomposition in these other additional zones being done under anaerobic conditions.

The method uses a primary reactor having a reaction zone charged with organic matter, said organic material decomposing in another zone of the reactor under aerobic conditions after an anaerobic decomposition period, the decompositions in any additional reaction zone being carried out. under anaerobic conditions.

The method can also implement a primary reactor having a plurality of reaction zones.

One of the zones is loaded with organic matter, then decomposed under aerobic conditions following anaerobic decomposition, the raw compost being extracted from another composting zone, following an aerobic decomposition, while the material organic in each of the additional zones of the reactor decomposes under anaerobic conditions.

The organic material entering the reactor is amended with additions to facilitate its decomposition, the organic matter charges being made so as to alternate layers of material to be treated and of material with drainage capacity, such materials with drainage capacity can be inorganic and therefore may remain present in the compost thus produced.

The bio-gas collected comes from both the primary reactor and the secondary reactor.

However, such a method seems to develop a slow kinetics of transformation of organic materials and not be able to assume or assume incomplete and insufficient, that is to say with a low yield, the depolymerization and / or the transformation of large molecules for example the cellulosic waste, hemicellulose, lignocellulose into simpler molecules likely to lead to the formation of bio-gas.

US 5,599,451 also describes an integrated anaerobic and aerobic process, but for the biotreatment of toxic waste in substantially liquid form. The process uses a reactor incorporating anaerobic / aerobic biotreatment methods. This reactor uses a biofilm that works by creating a decreasing oxygen gradient. This wastewater treatment method takes advantage of the best aspects of the aerobic process, which is inexpensive, and generates little sludge or bio-gas discharge and combines them with the methanogenic capabilities of the anaerobic process. This biological film consists of a granular bed of anaerobic sludge in suspension colonized by aerobic bacteria. This bio-reactor has a water inlet allowing the arrival of liquid waste, as well as two exits: one for the exit of treated water, the other for the release of gas. The anaerobic / aerobic biofilm of the bioreactor has an outer surface lined with aerobic bacteria as well as a central core harboring strict anaerobic bacteria and methanogenic bacteria. A decreasing gradient of oxygen concentration towards the core of the biological film is obtained by the controlled injection of a gas or an oxygen-containing liquid into the effluent liquid recycle loop. Biofilm allows aerobic and anaerobic treatment in a single system. The organization of the three-layer bio-film guarantees optimal conditions for the proliferation of different populations of microorganisms and protects the strict anaerobic bacteria of the nucleus from the harmful effects of oxygen. The stabilized biological film offers a flexible concept in that the core of the bio-reactor can also include inert micro-carriers, such as expanded clay particles or any other porous material meeting the requirements, in order to immobilize the cells and stabilize the biological film in suspension, maximizing coupling degradation of oxidative and reducing conditions. The frequency of re-circulation of liquids in the bio-reactor can be adjusted to provide better control over oxygenation and methane extraction. Inflow control minimizes residual oxygen production to maximize the combination of oxygen degradation and reduction. It is a sort of anaerobic / aerobic synchronous treatment of effluents containing chemical pollutants such as pesticides.

Such a process is however not oriented towards the dedicated production of methane and compost. Such a process is obviously very specific as to the type of organic material to be treated.

There is therefore an unmet need for a simple and inexpensive bioprocessing process that allows the valorization in the form of production of quality bio-gas and in the form of a quality by-product of the compost type, materials organic of various origins.

SUMMARY OF THE INVENTION Therefore, the object of the invention is to create a continuous process of biotreatment for effectively converting available organic materials of the same nature or of different natures, whether in the form of waste, in mixture or in the form of dedicated organic raw materials, in solid or other form, in two recoverable products, one in the form of bio-gas, most of which consists of methane and the other in the form of compost of good agronomic quality for soil conditioning.

The process, according to the invention, of continuous bio-treatment of organic matter of various vegetable and / or animal origins, by means of micro-organisms with a view to transforming said materials into energy biogas and into compost, characterized in that it uses, in successive phases of bio-transformation: a) an aerobic hydrolysis phase of the organic materials, b) an anaerobic phase of acidogenesis and acetogenesis of the hydrolysed organic materials, c) a phase anaerobic methanogenesis of organic materials transformed by acidogenesis and acetogenesis producing energy bio-gas, a concentrate and a liquid effluent; d) a phase of aerobic composting of the concentrate after solid / liquid separation.

DETAILED DESCRIPTION OF THE INVENTION The progress made in the field of bio-treatments of dedicated or available organic waste materials in the form of waste, makes it possible to obtain transformation products which are chemical intermediates and chemical or energetic products. directly usable by humans at low costs and reasonable processing efficiencies.

These renewable organic materials include all terrestrial or aquatic plants such as forest and agricultural residues, algae, peat, organic residues of peach, animal matter, consisting of carbohydrates, lipids and proteins.

As an illustration, if the only domain of all terrestrial and aquatic plants is examined, it appears that the main constituents of this plant are carbohydrates or carbohydrates, ie sugars and starches that are polysaccharides and lignocellulosic compounds.

In the particular case of lignocellulosic compounds, these compounds consist of cellulose, hemicellulose and lignin which are: for cellulose, glucose polymers hydrolyzable in an acid medium, for example, for hemicellulose, complex molecules of polysaccharides, for lignin, polymers of high chemical stability which makes it difficult to degrade by chemical or biological reagents.

However, according to the object of the invention, the process of biotransformation of organic materials by microorganisms which may be bacteria and / or yeasts takes place in three highly interdependent phases which are: A hydrolysis phase specific, through the action of strict aerobic hydrolytic bacteria, which circumvents the difficulties that anaerobic bacteria have to hydrolyze certain organic residues, such as lignocellulosic materials, this hydrolysis by aerobic bacteria having the capacity to depolymerize and to to transform the complex molecules of organic matter such as carbohydrates, lipids and proteins into simpler molecules and also to promote protein synthesis. A phase of acidogenesis and acetogenesis by the action of strict anaerobic bacteria transforming, by acidogenesis, the hydrolysed organic materials and in particular the monomers produced during the hydrolysis phase into fatty acids, alcohols, hydrogen and carbon dioxide (CO2) and products of acetogenesis in methane precursors, Finally a phase of methanogenesis by the action of strict anaerobic bacteria synthesizing methane from hydrogen and carbon dioxide and transforming organic acids such as acetic acid methane and carbon dioxide.

Thus, the bioprocessing method according to the invention involves, in each of its transformation phases, the presence of different bacteria and / or yeasts, strict aerobic and then strict anaerobic, bio-transformation and synthesis, adapted to available organic compounds. in each phase of bio-treatment and in physicochemical and biochemical conditions of specific development.

Moreover, the continuous process of biotreatment according to the invention practices the principles of: - bio-increase by inoculation of organic matter to be treated by means of bacterial populations and media selected and adapted to the metabolization of the organic matter to be treated; bio-fixation by retention of anaerobic bacterial strains on substrates that are the packing materials of anaerobic bioreactors, constituting fixing and growth supports for said bacterial strains to increase the in-situ concentrations. Furthermore, the biotransformation mechanisms can be accelerated by the addition of mixtures of exogenous strains that are particularly active with regard to pollutants present in the organic materials to be biotreated or resulting from the bio-transformation of said materials. organic, for example, micro-organisms capable of degrading aromatic compounds or other compounds.

The originality of the continuous process of bioprocessing, according to the invention, appears to lie in the implementation of a bioprocessing pathway separating the phases of the three biochemical operations, that is to say the hydrolysis phase of the organic matter, the acidogenesis and acetogenesis phase, and the methanogenesis phase.

The decomposition according to the invention of organic materials by bacteria takes place in four highly interdependent phases which describe a fermentation cycle: aerobic hydrolysis, anaerobic acidogenesis-acetogenesis, anaerobic methanogenesis and aerobic composting of the concentrates. Each step involves the activity of different bacteria, adapted to the available organic materials, under the conditions of specific development.

Cellulose, hemicellulose and lignin are the major macromolecules of many plants and products derived from them. During hydrolysis reactions, if hemicellulose and cellulose are easily broken by the bacterial medium, lignin is degraded very slowly under aerobic conditions and remains completely inert under anaerobic conditions. Some organic waste is rich in lignin.

The steps of acidogenesis and acetogenesis which follow see some microorganisms present use the compounds from the hydrolysis reactions for their own development and reject acidic organic molecules, especially acetic acid.

The final step of methanogenesis allows other bacteria to degrade the compounds derived from acidogenesis and acetogenesis by biotransforming them into methane (CH4) and carbon dioxide (CO2).

Each phase of the bioprocessing process according to the invention is examined below in detail.

Hydrolysis phase of organic matter

This bio-treatment phase is carried out aerobically by means of a seeding constituted of an inoculum whose quality and mass depend on the nature and quantities of the organic matter to be treated. This hydrolysis phase by biotreatment appears highly innovative in that: it makes it possible to promote the synthesis of proteins from the carbon and nitrogen organic compounds present; it transforms the organic nitrogen of the nitrogenous organic compounds present in order to increase the subsequent methanization yields of said organic compounds. The objective in this hydrolysis phase is to rapidly nitrify the nitrogen portion of the organic materials by converting the amino and ammonia nitrates present, into nitrites and nitrates in order to increase the yields of the methanogenesis phase.

To do this, the inoculum constituting the seeding is prepared so that it contains a defined mass of strict aerobic nitrification bacteria, such as for example nitrosomonas, nitrosoglae, nitrosocystis, nitrosospora, nitrobacter, and others, capable of carry out the nitritation and the nitratation of the organic matter to be treated in the presence of oxygen according to the following reactions:

NH4 + +3/2 02. 2H + + H20 + NO2-NO2 + + 1/2 02 -4.103- This aerobic hydrolysis bio-treatment phase also makes it possible to promote protein synthesis.

Therefore, carrying out this aerobic hydrolysis phase makes it possible to circumvent the difficulty that anaerobic bacteria have in hydrolyzing certain organic residues such as, in particular, the lignocellulosic waste associated with nitrogenous waste, which constitutes one of the major components of the organic waste to be treated. The continuous action of bacteria and / or associated enzymes makes it possible to optimize this hydrolysis phase in a role of preparing the organic matter to be treated for subsequent transformations by acid, aceto and methanogenesis. Large complex molecules of organic materials such as carbohydrates, lipids, proteins, are depolymerized and converted into simpler molecules by the action of hydrolytic bacteria such as, for example, Clostridium Thermocellum which converts cellulose to acetic acid and lactic acid.

The transformation of organic materials by this aerobic hydrolysis bi-treatment leads to the production of a biomass according to rapid bacterial synthesis. A short aerobic residence time is required not to amplify the ammonification which would favor the excess transformation of organic nitrogen into ammoniacal nitrogen by heterotrophic bacteria.

In this first hydrolysis phase, it is necessary to proceed with the seeding of the medium consisting of the organic material to be treated which is subjected to this hydrolysis. This seeding can be discontinuous or continuous.

The nature of the aforementioned strains constituting the inoculum differs according to the constitution of the organic materials to be treated.

Strains are produced sequentially in sterile fermenters. The selected bacteria and / or yeasts are first concentrated by centrifugation and then mixed. A growth medium and a supply of organic carbon and nitrogen in the form of amino acids are added.

The seed assembly is conveniently referred to as 3S inoculation and comprises: strains such as bacteria and / or yeasts; a carbon and nitrogen substrate, in particular carbohydrates and amino acids; - Mineral salts, containing the growth factors not included or in low concentration in the organic materials to be treated.

The seeded aerobic hydrolysis phase is carried out on rectified organic materials, that is to say the composition of which has been arranged, from contributions of specific carbonaceous constituents such as amino acids and / or extracts of yeasts and / or vitamins and other constituents.

The seeded aerobic hydrolysis phase additionally comprises a supply of enzymes derived from fermentation, in particular lipidic, proteinidic and carbohydrate enzymes. The mass of inoculum is defined for an initial dryness of between 12 and 40% by weight of moisture and preferably between 18 and 22

This dryness value of the hydrolysis phase is important for the following phases of acidogenesis-acetogenesis as well as for the methanogenesis phase because it facilitates the gas / liquid exchange.

According to the invention, this hydrolysis phase may require a supply of specific organic material in order to favor the yield of the following phases and in particular that of the production of methane.

An important characteristic of the hydrolysis phase of the bioprocessing process according to the invention is the carbon / nitrogen ratio (C / N) of the organic materials to be treated, this ratio having to be in the range of 15 to 15%. at 4015 and preferably between 20 and 30 when expressed by weight of presence of carbon and weight of nitrogen.

In the case where this ratio is less than 20, that is to say such that 12 <C / N <20, and in situations where there is inability to add a source of organic carbon, this ratio can be admitted in the state. In this case it will be necessary to control the transformation of the mineral nitrogen by the supply of nitrifying strains, and to take into account thereafter for the phase of acidogenesis whose pH will be brought back to a value close to 6.5 by introducing an acid such as, for example, orthophosphoric acid. In addition, a low C / N ratio implies an increase in the residence time during the acidogenesis phase.

In the same way, an excessively high C / N ratio leads to other disadvantages, in particular to inadequate conversion kinetics.

Therefore, the control of this optimum C / N ratio preferably between 20 and 30 requires the upstream preparation of the organic materials to be treated, combining organic materials carbon and / or nitrogen of various natures, origins, origins, as selected in the plant or animal world.

Aerobic hydrolysis requires a residence time of the order of about 2 days. The fermentation temperature in the hydrolysis phase after seeding by the aerobic inoculum depends on the composition of the organic matter to be treated. It can be in the range 25 to 40 ° C and preferably 30 to 37 ° C. In the case of an organic material to be treated consisting essentially of protein compounds from agro-food industries, this temperature can be mesophilic and of the order of 30 ° C. In the case of an organic material consisting essentially of compounds incorporating a cellulose fraction, a temperature of the order of 35 ° C promotes the conversion of cellulose to sugars under optimal conditions of medium and salinity provided by the medium. .

This phase of bio-transformation of organic materials by aerobic hydrolysis leads to the production of monomers which in the following phases are at least partly converted into fatty acids, alcohol, hydrogen and carbon dioxide.

In the context of the aerobic hydrolysis of the organic materials to be treated according to the invention, air is injected into the reaction medium to promote agitation of the mixture and oxygenation of the aerobic bacterial strains, and to allow the transformation of ammoniated and amine nitrogen to nitrite and nitrate.

The air flow rate is according to the composition and the nature of the organic materials to be treated of between 5 and 15 v / v / h, ie volume of air, per volume of treated material and per hour.

Finally, the aerobic hydrolysis medium can receive a liquid recycled fraction, rich in various components and in particular in bacterial strains.

Acidogenesis and Acidogenesis Phase A large proportion of the monomers produced by the aerobic hydrolysis of the organic material to be treated is converted during the acidogenesis phase into fatty acids, such as, for example, butyric, propionic and acetic acids. and alcohols such as ethanol, methanol, and hydrogen and carbon dioxide (CO2).

The bacterial populations involved in acidogenesis are strict anaerobes such as, for example, Ruminocula Clostridium, Bifido bacterium. After isolation, these strains can be produced in sterile fermenters and introduced by bio-increase into the acidogenesis reactor.

Acetogenesis Acetogenesis converts the products of acidogenesis into precursors of methane, in particular acetic acid, formic acid, hydrogen and carbon dioxide.

Transformation reactions of products resulting from acidogenesis during acetogenesis avoid the accumulation of volatile fatty acids other than acetic acid, which, at high concentrations, become inhibitors of methanogenesis.

Although most of the strains responsible for acetogenesis remain to be identified, the most well-known bacteria active in this phase are, for example, Desulfovibrio, Clostridium thermoaceticum, Clostridium Formioaceticum, Acebacterium Woodii.

All these species live in symbiosis with the bacteria of methanogenesis; they are also hydrogen consumers.

The control of acetic acid and formic acid formed is regularly carried out during this acidogenesis-acetogenesis phase, these two acids in particular being precursors of the formation of methane.

Products leaving the hydrolysis and entering the acidogenesis-acetogenesis phase are subjected to mixing and homogenization by mechanical means and / or by the use of an oxygen-free recycling gas stream.

The acidogenesis-acetogenesis phase maintains a high concentration of biomass, this biomass being formed by active anaerobic bacteria and / or yeasts, by biofixation at the internal periphery of the digester.

In order to prevent the formation of agglomerates between the organic matter particles, a surfactant surfactant may be added. Such a surfactant can be among those known, in particular those of polyoxyethylene type.

Methanogenesis Phase The methanogenesis phase makes it possible to synthesize methane, in particular from hydrogen and carbon dioxide, according to the reaction: CO2 + 4H 2 -eM 4 + 2H 2 O

and from acetic acid according to the reaction: CH3-COOH ù> CH4 + CO2

The bacteria involved in methanogenesis are strict anaerobes and are selected from the group consisting of, inter alia, Methanobacterium, Thermoantrophicum, Methanosarcina Barkeri and the like.

In general, the methanogenesis phase takes place at a temperature of between 30 ° C. and 55 ° C.

Some strains have an optimum growth rate at mesophilic temperatures between 30 and 45 ° C. However, most species show optimum growth at thermophilic temperatures between 50 and 55 ° C.

The pH of the medium of the methanogenesis phase is in the range between 7 and 7.5. Growth kinetics are slow, 5 to 6 times slower than acidogenic bacteria, resulting in a longer residence time in the methanogenesis digester. Some bacteria live in association, such as, for example, Desulfovibrio organisms in the presence of Methanobacterium MOH, sulphate-reducing bacteria in the presence of methanogenic bacteria, which allows the realization of thermodynamically impossible reactions.

The four major groups of methanogenesis bacteria are still associated in methanolic fermentations and require reasoning in terms of mixed cultures, these groups being well known from the state of the art.

Aerobic composting phase The aerobic composting treatment of the concentrates resulting from the methanogenesis phase after solid / liquid separation is carried out by means of aerobic strains according to any method well known in the state of the art.

Parameters of the process according to the invention

The implementation of an aerobic pre-treatment, ie aerobic hydrolysis according to the invention, and the diversity of the microorganisms involved in all the phases of the bio-treatment process make it possible to the easier the optimal conduct of the methanic fermentation depending on the parameters of the anaerobic digestion. At each stage, the activity of the deployed strains may be complementary or inhibitory. In addition, the diversity of the organic materials to be treated makes it all the more difficult to conduct the algorithm that guarantees the best yield of methane synthesis.

To allow an optimization of each phase, the continuous process of bio-treatment, takes into account the difference of the parametric constraints of each phase, ie those of hydrolysis, acidogenesis and acetogenesis and methanogenesis.

Aerobic pre-treatment, ie the phase of aerobic hydrolysis of organic materials, associated with the separation of the anaerobic phases, acid / acetogenesis on the one hand and methanogenesis on the other, aims to use as rationally as possible a wide variety of strains whose functions may have complementary or inhibitory effects.

Depending on the nature of the organic materials to be treated, and objectives of methane synthesis, it is necessary to control the fermentation parameters by using the use of industrial sensors and control assemblies placed at each stage of treatment.

Temperature parameters During the hydrolysis phase, and although the fermentation is exothermic, the aerobic pre-treatment can be carried out at ambient temperature, possibly controlled. However, the choice of a low residence time does not allow to rise to a desired optimum temperature such as of the order of 30 ° C to 35 ° C depending on the nature of the organic material to be treated.

In general, the unwinding temperature of the hydrolysis phase is in the range 25 ° C to 40 ° C and preferably 30 ° C to 37 ° C. The installation of a heat exchanger makes it possible to stabilize the temperature and to optimize the hydrolysis yield.

During the acidogenesis and acetogenesis phase, the temperature selected for the acidogenesis is between 40 ° C and 50 ° C depending on the nature of the organic materials to be treated. An internal exchanger makes it possible to regulate the temperature. During the methanogenesis phase, the production of methane passes through two optima, one in the mesophilic zone at 40 ° C and the other in the thermophilic zone around 50 ° C. Maintaining a regulated temperature in the digester in the smallest possible range is one of the conditions required for the proper functioning of the fermentation. The advantages and disadvantages of methane fermentation in the mesophilic or thermophilic zone are well known: For the mesophilic pathway, there is less water vapor and less CO2 in the gas produced, which allows an easier valuation for biogas. In addition, the spectrum of methanogenic microbial species is wider. Finally, the energy balance is more favorable, because of the possibility of using low temperatures

For the thermophilic path, there is greater reactivity, which results in a lower retention time. There is also a decrease in the volume of sludge formed, and destruction of pathogenic and phytopathogenic microorganisms. Finally, the maintenance of anaerobic conditions is facilitated.

In general, the temperature of the methanogenesis phase can be between 35 and 55 ° C., depending on whether mesophilic or thermophilic conditions are being sought.

In a very preferential manner, the continuous process of biotreatment according to the invention retains the thermophilic route because of the guarantees of hygienization provided and the maintenance of anaerobic conditions. The optimization of the residence time is also involved in this choice, as well as concerns5 reduction of the volume of work, important factor to minimize the energy expenditure attributed to heating.

PH parameters The pH value is defined according to the treatment phases. The values are between 6.5 and 8.

During the hydrolysis phase, the aerobic fermentation of the organic compounds constituting the organic material to be treated before any treatment is carried out at a pH close to neutrality, that is to say at a pH of between 6.5 and 7. As the residence time is reduced, the initial pH of 6.5 can increase in 36 hours to reach 7, and this, for aeration of, for example 15 volume of air / volume of organic material to be treated / hour (v / v / h). If it is necessary to reduce the pH to a value between 6.5 and 7, the use of an acid is practiced. Ortho-phosphoric acid is preferred to simultaneously adjust the value of the PH and compensate for any phosphorus deficiencies that may be observed at the end of the methanation.

On the one hand, it is a question of creating a compost of good agronomic quality and, on the other hand, of managing the liquid effluent leaving the methanisation after solid liquid so that this liquid effluent has a ratio between: biological demand in oxygen, nitrogen content, phosphorus content compatible with the required ratio, ie BOD / N / P of 100/5/1.

Conversely, an initial pH that is too low will be corrected by adding an alkaline agent, in particular soda or lime.

During the acidogenesis-acetogenesis phase, a decrease in pH below 6.5 can result in a high concentration of volatile fatty acids and results in an inhibition of methanogenesis.

During this same phase of acidogenesis - acetogenesis a pH greater than 8 promotes the formation of hydrogen, ammonia and hydrogen sulphide at the expense of methane production. Thus, the pH of the anaerobic acidogenesis-acetogenesis phase is carried out at a pH in the range 6.5 to 8.

PH balance is provided by a correctional officer; bicarbonate which can easily be dissolved in the aqueous medium is preferred. The bicarbonate concentration must be of the order of 1500 mg / l in order to maintain the pH of the aqueous medium in the abovementioned range, and this to ensure the anaerobic fermentation with a view to maximum yield of energy bio-gas.

During the methanogenesis phase, for most of the organic materials to be treated, the optimum pH of the methanogenesis is between 7 and 7.5.

Given the buffering capacity of the medium, it is rarely necessary to correct the pH during methanogenesis. If necessary, it can be reduced, for example, with lime milk. Soda ash will be avoided due to the risk of excess Na + cations in the compost formulated from the final sludge.

Resistance time parameters The residence time of the organic materials to be treated, in the installations making it possible to implement the continuous biotreatment process according to the invention, is defined from the composition of said organic materials to be treated, parametric conditions. of functioning, characteristics of the effluents resulting from the digestion. This parameter is decisive for sizing each step of the process. Preferably, a volume load of organic material to be treated as high as possible will be considered, in order to optimize the size of the equipment and thus reduce the cost of digestion equipment.

During the aerobic hydrolysis phase, a residence time between 36 and 72 hours is required, depending on the nature of the organic materials to be treated, the effective size of the suspended solids and the C / N ratio.

During the acidogenesis and acetogenesis phase, the residence time is defined from the kinetics of the bacterial populations adapted to the degradation of the organic matter to be treated. The bio-fixation inside the reactor makes it possible to maintain the concentration of the active mass of the strains according to the organic load to be treated. Depending on the materials constituting the entrants, the residence time of the acidogenesis - acetogenesis phase is between 12 and 15 days.

During the methanogenesis phase, the growth rate of the strains responsible for methanogenesis is low and most species are sensitive to parametric fluctuations. Bio-fixation makes it possible to maintain a constant mass of bacteria in the bio-reactor. If strains inhibiting compounds are present, the retained active mass reduces the incidence of toxic effects. The residence time of the methanogenesis is generally between 20 and 50 days. According to the organic matter and according to the majority of the cases to treat it is between 36 and 42 days. This residence time is reduced when there is sludge recycling and can, for some organic materials to be treated be between 25 and 30 days.

Parameters of redox potential The medium must be reducing and maintained reductive throughout the acidogenesis - acetogenesis and methanogenesis phases, which implies the absence of oxygen. In order to avoid the introduction of oxidizing elements into the reactors, it is necessary to assume the perfect seal. The anaerobic bacterial populations preferentially act at low redox potential of between -300 to -330 mV. Consequently, the control of the redox potential is carried out regularly, preferably every day, on the median part of the anaerobic reactors.

Parameters constituted by mineral nutrients and inhibitors The constitution of the medium formed by the organic matter to be treated in the presence of water differs for each phase of the process, hydrolysis, acetogenesis and acidogenesis, methanogenesis.

The C / N ratio is the benchmark for quantifying the distribution of mixtures of organic materials to be treated.

For the hydrolysed fraction, it is easy to subtract the aqueous portion and proceed to Carbon, Nitrogen, Phosphorus analysis to determine ratios C / N, C / P, and BOD / N / P.

Preferably, the BOD / N / P ratio of the liquid effluent leaving the methanogenesis after the desired solid liquid separation must tend towards the well-known ratio 100/5/1.

The strict anaerobic portion of the treatment requires an optimal C / N of 32 to 35 and a C / P ratio of 150. Nitrogen is generally provided by organic materials from agro-food industries, while carbon comes mainly from agricultural products such as that for example wheat, corn. In the majority of inputs, nitrogen is in sufficient quantity that the methanogenesis phase does not produce biomass and consumes very little nitrogen.

The nitric nitrogen content (NO3) must be controlled at the level of methanogenesis because its oxidizing power has the effect of raising the redox potential. The concentration of sulphates must be controlled at the acidogenesis-acetogenesis and methanogenesis phases.

The sulphate content should not exceed 100 to 200 mg / l in these two phases of acidogenesis-acetogenesis and methanogenesis. Sulphates are inhibitors of methanogenesis. They lead to the production of hydrogen and hydrogen sulphide, the corrosive effects of which are damaging to equipment.

It is nevertheless admitted that a small amount of hydrogen sulphide and hydrogen can have a favorable effect insofar as the redox potential is lowered. This also induces the precipitation of toxic cations such as Cu, Zn, Ni, Hg, Fe, Pb, in the form of sulphides. All heavy metals have bacteriostatic or bactericidal effects, even at low concentrations.

Agitation parameters The agitation of the medium makes it possible to maintain the homogeneity of the organic matter to be treated and the inoculum associated with nutrients and other additions, in order to constitute an active biomass. In addition, agitation promotes heat exchange and participates in the degassing of sludge. Several modes of agitation can be implemented within the framework of the continuous process of biotreatment according to the invention: mechanical agitation from turbines placed on the surroundings; agitation from the recirculation of gases or effluents. The gases can be recirculated and dispersed by booster at the base of the reactor. The effluents, after simple decantation, can be recycled at the base of the digesters.

However, the method according to the invention proposes, in addition to these technologies, a mode of degassing and recycling by internal recirculation using the same energy source for the hydraulic recycling and the transfer of gases. Such a technique also ensures the thermal homogeneity of the biotreatment reactor commonly called digester.

The recycle rate of the gases is 10-12 v.v.h when expressed in volume of gas per m3 of organic material to be treated in the biotreatment reactor and per hour. This re-circulation promotes the exchange between the organic matter and the bacteria by increasing the contact rate at the level of the peripheral biolocation of the biotreatment reactor. For this purpose the height of the gas diffuser is one third of the water height of the biotreatment reactor.

The internal pressure of the biotreatment reactor is maintained from an external column consisting of a gooseneck pipe equal in height to the liquid height for the digester.

The digester can be equipped with a valve calibrated between 18 and 25 mm of pressure. However, the simplest solution is to directly store the gases in flexible gasometer at the end of the digester.

Finally, the liquid and solid effluents are separated and stored in order to undergo recovery treatments and / or compliance with environmental requirements.

Thus, the continuous bioprocessing process according to the invention appears to be particularly interesting and useful for the bio-transformation of organic matter of plant and / or animal origin into energy biogas, and compost of agronomic quality.

FIG. 1 represents the assembly of a plant for the biotreatment of organic materials implementing the method of the invention making it possible to obtain a bio-gas rich in methane and a compost of good agronomic quality and thus easily recoverable.

The initial flow "A", ie the organic matter to be treated for its transformation into biogas and compost, consists of crushed organic residues of predominantly vegetable and animal origin. These crushed organic residues are mixed and homogenized at an inlet hopper (1).

The introduction of aerobic bacterial strains, "B", is done by means of an injection device located in the feed zone of the type, for example metering screw (2) of the hydrolysis tank (3) operating in aerobic diet.

The flow to be treated "A", loaded with bacterial strains "B", is successively subjected to the three treatment phases mentioned above, respectively in the hydrolysis tank (3), the anaerobic biotreatment reactor (4) in which operates the acidogenesis and acetogenesis phase, and the anaerobic digester (5) in which the methanogenesis phase takes place.

The formulated organic material, constituting the initial flow to be treated "A", loaded with bacterial strains "B", is suspended in water and is aerated by means of a stream of air coming from the compressor (7). The flow rate of air circulation is at least 10 v / v / h and preferably varies between 20 and 30 v / v / h. A vent (8) allows the evacuation of aeration air and brewing.

The anaerobic biotreatment reactor (4), in which the acidogenesis and acetogenesis phase operates, is provided with a stirring system (9) and packing materials (10) for the bio-fixation by retention of the strains. anaerobic bacterial population. The products resulting from acidogenesis and acetogenesis, are conducted via a pipe (11) in the methanogenesis reactor, that is to say the digester (5). The gaseous effluents resulting from the reaction of acidogenesis and acetogenesis are conducted via line (12) in the storage tank (6) of the energy biogas produced.

The digester (5) is provided with a gas circulation (13) operating via a partial recycling of the biogas produced during the methanogenesis and which allows the regular stirring of the organic products resulting from the acidogenesis and the 'acetogenesis. The digester (5) is also provided with packing materials (14) for retention bio-fixation of anaerobic bacterial population strains. The evacuation of the methane flow takes place via a pipe (15) opening into (12) and leading into the storage tank (6) through the pipe (16).

A solid / liquid / gas separator (18) is fed via the pipe (17) with effluents from the digester (5). Within this separator, a separation occurs in three phases, a gas phase evacuated through the pipe (19) to the reservoir (6), a decanted solid phase exiting through the pipe (20), a portion of which is recycled by the pipe (21) in the pipe (11), for reintegration into the digester (5) and the other part is discharged through the pipe (22) for treatment in accordance with a valued agricultural use .

As for the liquid phase, it is evacuated via the pipe (23) to a biological treatment unit, at least a portion of which can be withdrawn and conducted via line (24) into the aerobic hydrolysis reactor (3). ).

Claims (24)

1. Process for the continuous biological treatment of organic matter of various plant and / or animal origins, using microorganisms for the purpose of transforming said materials into energetic bio-gas and into a compost, characterized in that it implements in successive phases of bio-transformation: a) a phase of aerobic hydrolysis of organic matter, b) a phase of acedogenesis and anaerobic acetogenesis of hydrolysed organic matter, c) a phase of anaerobic methanogenesis of materials organic transformed by acidogenesis and acetogenesis, producing energy bio-gas, a concentrate and a liquid effluent; d) an aerobic composting phase of the concentrate after solid / liquid separation. 2. biotreatment process according to claim 1, characterized in that the aerobic hydrolysis phase is seeded into microorganisms in a continuous or discontinuous manner. 3. Biotreatment process according to either of claims 1 or 2, characterized in that the aerobic hydrolysis phase is seeded into microorganisms using an inoculum comprising: aerobic strains of bacteria and or yeasts-a carbon and nitrogenous substrate comprising in particular carbohydrates and amino acids; mineral salts, containing growth factors of bacteria and / or yeasts not included or in low concentration in the organic materials to be treated 4. biotreatment process according to any one of claims 1 to 3, characterized in that the aerobic microorganisms are bacteria and / or yeasts nitrification and bacteria and / or hydrolytic yeasts. 5. Continuous bioprocessing process according to at least one of claims 1 to 4, characterized in that the seeded aerobic hydrolysis phase is carried out on organic materials rectified by means of contributions of specific carbonaceous constituents. 6. Continuous bioprocessing process according to claim 5, characterized in that the specific carbonaceous constituents are amino acids and / or yeast extracts, and / or vitamins. 7. Continuous bioprocessing process according to at least one of claims 1 to 6, characterized in that the seeded aerobic hydrolysis phase comprises a supply of enzymes derived from fermentation, in particular lipid, proteinid and carbohydrate enzymes. 8. Continuous bioprocessing process according to at least one of claims 1 to 7, characterized in that the aerobic hydrolysis seed phase seeded requires a carbon / nitrogen ratio (C / N) between 15 and 40 and preferably between 20 and 30 . 9. Continuous bioprocessing process according to at least one of claims 1 to 8, characterized in that the seeded aerobic hydrolysis phase is carried out at a temperature between 25 ° C and 40 ° C and preferably between 30 ° C and 37 ° C. 10. Continuous biotreatment process according to at least one of claims 1 to 9, characterized in that the aerobic hydrolysis phase takes place at a pH of between 6.5 and 7. 11. Continuous bioprocessing process according to at least one of claims 1 to 10, characterized in that the organic material entering the aerobic hydrolysis phase has a dryness of between 12 and 40% and preferably between 18 and 22%. in weight of moisture. 12. Continuous biotreatment process according to at least one of claims 1 to 11, characterized the pH of the acidogenesis-acetogenesis phase is adjusted by addition of acid, preferably orthophosphoric acid. 13. Continuous bioprocessing process according to at least one of claims 1 to 12 characterized in that the acidogenesis-acetogenesis phase comprises a control of acetic acid and formic acid formed. 14. Continuous bioprocessing process according to at least one of claims 1 to 13, characterized in that the acidogenesis-acetogenesis phase maintains a high concentration of active anaerobic bacteria and / or yeasts by bio-fixation at the periphery of the digester. acidogenesis-acetogenesis. 15. Continuous biotreatment process according to at least one of claims 1 to 14, characterized in that a surface-active surfactant is added to the acidogenesis-acetogenesis phase. 16. Continuous bioprocessing process according to at least one of claims 1 to 15, characterized in that the acidogenesis-acetogenesis phase takes place at a pH of between 6.5 and 8. 17. Continuous bioprocessing process according to at least one of claims 1 to 16, characterized in that the acidogenesis-acetogenesis phase is carried out at a temperature between 40 ° C and 50 ° C. 18. Continuous bioprocessing process according to at least one of claims 1 to 17, characterized in that the pH is maintained throughout the methanogenesis phase to a value between 7 and 7.5. 19. Continuous bioprocessing process according to at least one of claims 1 to 18, characterized in that the methanogenesis phase is carried out at a temperature in the range of 30 ° C to 55 ° C. 20. Continuous biotreatment process according to at least one of claims 1 to 19, characterized in that the methanogenesis phase takes place under a controlled redox potential at a level between -300 and -330 mV. 21. Continuous bioprocessing process according to at least one of claims 1 to 20, characterized in that the concentrate from the methanogenesis is separated from the liquid effluents and then recycled partly into the methanogenesis phase. 22. Continuous bioprocessing process according to at least one of claims 1 to 21, characterized in that the methanogenesis phase maintains a high concentration of active bacteria and / or anaerobic yeasts by bio-fixation at the periphery of the methanogenesis digester. 23. Continuous biotreatment process according to at least one of claims 1 to 22, characterized in that the homogeneity and the mixing of the organic material during the methanogenesis phase is effected by means of a re-circulating system. bio-gas. 24. Use of the bioprocessing process according to at least one of claims 1 to 23, the transformation into energetic bio-gas and compost of organic matter of plant and animal origin.