Method for determining the mass proportion of additive to be injected into a digester

Abstract

A method for determining (1) a mass proportion of an additive to be injected into an anaerobic digester, said additive being intended to promote at least one reaction of degradation of organic matter by microorganisms, said method comprising: - a step of acquiring (2) one or more samples of said digestate, each sample being enriched by a first concentration of a compound inhibiting anaerobic digestion and by a second concentration of another compound chosen from the products of acidogenesis; - an analysis step (3), during which, for each sample, a mass proportion of said additive is added, and a methane production kinetic is measured; - a step (4) of determining from said analyses (4) a relationship between the mass proportions of additive added and the methane production kinetics;- a step (5) of predicting a parameter representative of the maximum activity of microorganisms, and - a step (6) of determining the mass proportion of additive to be added to said input. Figure of the abstract: Figure 1;

Description

Title of the invention: Method for determining a mass proportion of additive to be injected into a digester Field of invention

[0001] The invention relates to the field of digesters, also called biogas reactors or methanizers.

[0002] More particularly, the invention relates to a method for determining a mass proportion of additive to be injected into a digester. The additive being capable of promoting at least one reaction of degradation of the organic matter by microorganisms in the digester. State of the art

[0003] It is known that anaerobic digestion is a key process for recovering energy present in various organic materials, including by-products of many industries as well as energy crops. This technology is used to process these organic materials, in order to produce biogas, which is a renewable energy source and can be used to produce biomethane, electricity or heat. This process is also used in wastewater treatment plants to treat residual sludge and reduce its volume while producing biogas.

[0004] Anaerobic digestion is a cascade of biochemical reactions that convert the organic matter present in the digester into biogas, which is mainly a mixture of carbon dioxide and methane. The remaining materials are called digestate.

[0005] This process is intrinsically complex because:

[0006] - each degradation step is carried out by groups of microorganisms distinct, each having their own kinetics, optimal growth conditions and specific inhibitory compounds;

[0007] - these groups of microorganisms interact with each other, which can result in example in phenomena of competition or syntrophy;

[0008] - the operating conditions of the process, such as the feeding mode as well as the nature of the input or even the temperature, strongly influence the kinetics of these groups of microorganisms.

[0009] This complexity makes the sizing of reactors and the operation of this process relatively difficult.

[0010] In addition, inhibitory compounds frequently present in anaerobic digestion such as ammonia (NH3) and hydrogen sulfide particularly affect certain groups of microorganisms leading to a significant reduction in the methane productivity of the process.

[0011] The management of these compounds is therefore crucial for the proper functioning of anaerobic digestion processes, with priority given to sites treating inputs rich in nitrogen and sulfur.

[0012] Currently, several methods for managing these compounds and the resulting drop in process productivity are used, including the addition of an additive that promotes at least one reaction taking place in the digester, such as trace elements or biochar. An additive is a substance added to a reactant or product to improve its characteristics or those of the reaction. Among the additives of interest for digestion, we can, for example, cite trace elements or biochar.

[0013] The mechanism associated with the improvement of anaerobic digestion by additives is not always fully known. For example, in the case of trace elements, it is known that they are necessary for the production of enzymes by anaerobic flora. However, the necessary and optimal quantity is not known, particularly given the high variability of inputs, microorganisms, trace elements and the lack of control of their bioaccessibility in additives. In the case of biochar, numerous mechanisms and effects are cited in the literature, at different levels of evidence. For example, the use of additives as a support for biofilm growth, for the adsorption of inhibitors, the improvement of buffering capacity and the promotion of direct electron exchange thanks to its conductivity and redox properties. In addition, cross-effects are potentially present. For example, biochar could constitute in itself a supply of trace elements.Added to this difficulty is the fact that the associated mechanisms and reactions will be highly dependent on the operating parameters of the digester, in particular the temperature and the pH.

[0014] Indeed, certain additives make it possible to temporarily capture electrons from a donor and then transfer them to an acceptor thanks to its electrical conductivity and its surface chemistry. In addition, at high NH3 concentrations, methane production is carried out by hydrogenotrophic archaea (microorganisms) which are less sensitive to inhibition by NH3. These archaea depend on a delicate syntrophy from a thermodynamic point of view and their substrate (dihydrogen) is largely produced by so-called syntrophic bacteria degrading propionate and acetate, this reaction being unfavorable at a high partial pressure of dihydrogen.In this case, low activity of these bacteria can result in an accumulation of volatile fatty acids, which can cause a drop in pH capable of inhibiting the methanogenic biological activity of the digester and can produce concentrations of volatile fatty acids that inhibit the reaction from a thermodynamic point of view. Additives facilitate this relationship because they can potentially . replace dihydrogen in the transfer of electrons between these bacteria and archaea.

[0015] The use of an additive can therefore be an effective means of improving the efficiency of the process. However, the optimal dose of additive to be injected during anaerobic digestion is not necessarily identical depending on the process input and the operating parameters.

[0016] Thus, there is a need for a method for determining the optimal mass proportion of additive to be added in order to carry out optimal sizing and / or control of the process. Summary of the invention

[0017] A method is proposed for determining a mass proportion of additive to be injected into an anaerobic digester suitable for producing digestate and biogas containing methane, from an input comprising organic matter, said additive being intended to promote at least one degradation reaction of the organic matter by microorganisms in said digester, said method comprising:

[0018] - a step of acquiring one or more representative samples from said digestate from the digester, each sample being enriched by a first concentration of a compound inhibiting anaerobic digestion and by a second concentration of another compound chosen from the products of acidogenesis;

[0019] - an analysis step, during which, for each sample acquired, we add to the enriched sample a mass proportion of said additive, and a methane production kinetics is measured, the mass proportions of additive being distinct for each sample;

[0020] - a step of determining from said analyses a relationship between the pro mass portions of additive added and methane production kinetics;

[0021] - a step of predicting a parameter representative of the maximum activity of the mi organisms based on said determined relationship, and

[0022] - a step of determining the mass proportion of additive to be added to said input as a function of the parameter representative of the maximum activity of the predicted microorganisms.

[0023] This method makes it possible to determine the optimal mass proportion of additive to be added in order to carry out optimal sizing and / or control of an anaerobic digester. For this, the measurements and experiments are carried out under conditions that are not very favorable to digestion with high concentrations of another compound chosen from the products of acidogenesis such as propionic acid and in an inhibitor molecule. Although unfavorable, these conditions are those where the additive can maximally promote the appearance of a syntrophic relationship between the different species of microorganisms present to consume the other compound chosen from the products of acidogenesis and thus improve the efficiency of digestion.

[0024] In addition, the input of a digester is very variable in terms of composition and concentration of organic matter present, thus creating instability of the digester which makes its operation difficult. The use of this process will make it possible to overcome this constraint since the concentration of the additive to be injected will be adapted according to the digestate modified by the input.

[0025] Advantageously and in a non-limiting manner, the additive is chosen from biochar, iron oxide, activated carbon and / or a trace element such as iron, nickel, cobalt, molybdenum, selenium, tungsten, zinc, and tin.

[0026] Optionally, during the analysis step, the mass proportion of additive is between 1 g / kg and 50 g / kg inclusive for biochar, iron oxide or activated carbon or 0.01 to 10 mg / kg of input organic matter for one or more trace elements individually or as a mixture.

[0027] The proportion differs depending on the type of additive to be used because their effect does not translate to the same intensity and the microorganisms present do not have the same needs depending on the type of additive to be injected.

[0028] Advantageously and in a non-limiting manner, during the enrichment of the sample, the inhibiting compound is chosen from ammoniacal nitrogen, a heavy metal, a chlorophenol, a halogenated aliphatic compound, a pesticide, an antibiotic, and a lignocellulose hydrolyzate.

[0029] The inhibitory compounds that can be chosen are compounds usually present in digestion. They can be chosen according to the species of microorganisms present in the digester.

[0030] Optionally, the inhibiting compound is ammoniacal nitrogen at a first concentration of at least 1 g / L.

[0031] Optionally, when enriching the sample, the second concentration of another compound chosen from the products of acidogenesis is at least 1 g / L.

[0032] The temperature and / or pH can also be varied concomitantly in order to optimize these two major operating levers and to quantify their impact in synergy with the supply of additives. An experimental design can be implemented in order to reduce the number of conditions to be tested (eg, Box-Behnken at 3 levels of biochar concentration, trace elements and temperature).

[0033] Advantageously and in a non-limiting manner, the parameter representative of the maximum activity of the microorganisms is chosen from a specific growth rate of the microorganisms in the digestate and / or a maximum rate of methane production.

[0034] The invention also relates to a method for controlling a proportion mass of additive to be injected into a digester suitable for producing digestate and biogas, containing methane, in which:

[0035] - a mass proportion of additive to be injected is determined by the method of determining mination described above; and,

[0036] - the determined mass proportion of additive is injected into the digester.

[0037] The invention also relates to a device for determining a mass proportion of additive to be injected into an anaerobic digester adapted to produce a digestate and biogas containing methane, from an input comprising organic matter, said additive being intended to promote at least one degradation reaction of the organic matter by microorganisms in said digester, said device being characterized in that it comprises:

[0038] - means for acquiring one or more representative samples of said digestate from the digester and the enrichment means, from each sample, in a first concentration of an anaerobic digestion inhibitor compound and in a second concentration of another compound chosen from the products of acidogenesis;

[0039] - means for analyzing each acquired sample, comprising means adding, to the enriched sample, a mass proportion of said additive, and means for measuring methane production kinetics;

[0040] - means for determining a relationship between the mass proportions additive and methane production kinetics;

[0041] - means for predicting a parameter representative of the maximum activity of the microorganisms according to said determined relationship, and,

[0042] - means for determining the mass proportion of additive to be added to said input as a function of the parameter representative of the maximum activity of the predicted microorganisms.

[0043] The invention also relates to a device for controlling a mass proportion of additive to be injected into a digester adapted to produce digestate and biogas, containing methane, comprising:

[0044] - the determination device described above; and,

[0045] - means for injecting the determined mass proportion of additive into the digester.

[0046] The injection of the additive can be carried out at all levels in the digestion circuit, whether at the level of the input pipe, the digestate in the digester or at the level of the recirculation pipe.

[0047] Other features and advantages of the invention will emerge from reading the description given below of a particular embodiment of the invention, given for information purposes, but not as a limitation, with reference to the appended drawings in which:

[0048] [Fig.l] [Fig.l] is a flowchart of the determination method according to the invention;

[0049] [Fig.2] [Fig.2] is a curve illustrating methane production as a function of the time following the percentage of biochar added at a fixed temperature of 42.5°C;

[0050] [Fig.3] [Fig.3] is a curve illustrating the quantity of methane produced in log in function of time;

[0051] [Fig.4] [Fig.4] is a curve illustrating the different specific growth rates calculated for different doses of trace element, with or without addition of 1% biochar and different digestion temperatures.

[0052] Determination method

[0053] The determination method according to the invention aims to determine an optimal mass proportion of additive to be injected into an anaerobic digester in order to best promote at least one reaction of degradation of the organic matter by microorganisms in the digester.

[0054] The determination method according to the invention is also applicable for calculating the mass proportion of additive to be injected into a biological process such as fermentation by microbial communities in order to promote the fermentation reaction.

[0055] Each digester, due to the composition of the input preferably corresponding to any input comprising fermentable organic matter or anaerobic reactions involved, has different performances and consequently different optimal operating conditions. The addition of certain additives has the advantage of improving the performance of the process while allowing it to be used as a biofilm support for the development of microorganisms present in the digester.

[0056] By calculating the optimal mass proportion of additive to be injected, the process can thus be designed and / or operated in such a way as to obtain maximum yield and productivity in biogas.

[0057] The additive to be injected is chosen from biochar, iron oxide, activated carbon and / or trace elements in more or less pure solutions or in a mixture, adsorbents such as zeolite and ferrous / ferric reagents. The additive to be injected can also be a combination of these elements. Preferably, the additive chosen is biochar.

[0058] Biochar is a solid coal resulting from the pyrolysis of biomass, the properties of biochar differ depending on the pyrolyzed biomass and the process used. The choice of biochar is not limited to its origin, however for each biochar of different origin used, it will be necessary to reapply the determination method according to the invention to modify the optimal mass proportion to be injected.

[0059] Trace elements, also called trace elements, are chemical elements present in small quantities in nutrients essential for the development of living organisms. Trace elements are notably chosen from Iron, Nickel, Cobalt, Molybdenum, Selenium, Tungsten, Zinc, and Tin.

[0060] With reference to [Fig.l], the determination method 1 according to the invention firstly comprises a step 2 of acquiring one or more samples of the digestate from the digester which will serve as inoculum. The inoculum being a sample intended to be introduced into a favorable or unfavorable environment in order to study it.

[0061] The determination method 1, according to the invention, can be carried out before the construction of the digester and during its dimensioning. In this case, the samples will be acquired from pilot digesters or an already existing digester whose composition of the input and digestate is close to those which will be used by the digester under construction.

[0062] During acquisition step 2, each sample is enriched with a first concentration of an inhibitory compound and a second concentration of another compound chosen from the products of acidogenesis.

[0063] Inhibitory compounds are compounds that affect certain groups of microorganisms present within the digester. Thus, if the concentration of these compounds increases, then the productivity of the digester will greatly decrease.

[0064] When enriching each sample, the inhibitor compound is chosen from ammoniacal nitrogen, heavy metals, chlorophenol, halogenated aliphatics, pesticides, antibiotics, and lignocellulose hydrolysates. Preferably, the inhibitor compound is ammoniacal nitrogen.

[0065] The other compound chosen from the products of acidogenesis corresponds to an intermediate compound of digestion produced during the acidogenesis step. This compound may also be an inhibitor of the reaction. It may be volatile fatty acids, ethanol or lactic acid. Preferably, the other compound chosen from the products of acidogenesis is propionic acid.

[0066] The enrichment of each sample thus aims to place the microbial flora of the digester in “stress” conditions, that is to say in conditions that inhibit digestion. These conditions only allow the degradation of propionate into dihydrogen, which will be consumed by the bacteria present, in particular the hydrogenotrophic archaea. For this, the first concentration of ammoniacal nitrogen is at least 1 g / L and the second concentration of another compound chosen from the products of acidogenesis is at least 1 g / L. The choice of the first and second concentrations is made according to the microbiology of the inoculum and the expected kinetics of biodegradation of the carbon and nitrogen of the digester inputs.

[0067] Then, the determination method 1 comprises an analysis step 3, during which, for each sample acquired, a mass proportion of the additive for which the mass proportion to be injected is to be determined is added to the enriched sample, and a methane production kinetics is measured (corresponding to the quantity of methane produced over time), the mass proportions of additive being distinct for each sample.

[0068] This step 3 is implemented for each sample acquired, so the more samples there are, the more precise the mass proportion of additive to be injected will be determined.

[0069] For each implementation, the mass proportion of additive is different from the others and the portion of enriched input is distinct from the others. This makes it possible to obtain methane production kinetics for different proportions of additive and thus determine the optimal quantity subsequently.

[0070] The mass proportion of additive is chosen from a range which differs according to the nature of the additive. For example, the range differs according to whether the additive is biochar or a trace element. If the additive is biochar, an iron oxide or activated carbon then the mass proportion is for example between 1 g / kg and 50 g / kg of input organic matter inclusive whereas if the additive is a trace element then the mass proportion is for example between 0.01 to 10 mg / kg of input organic matter for one or more trace elements individually or as a mixture.

[0071] The kinetics of methane production is then measured from the measurement of the pressure or flow rate of gas produced and the study of the composition of the gas, thus making it possible to know the proportion of methane.

[0072] During analysis step 3, the temperature is also set because it can influence the digestion performance. For example, the temperature is between 20°C and 40°C, i.e. in the mesophilic range. Alternatively, the temperature is between 40°C and 60°C, i.e. in the thermophilic range. Generally, it is set according to the nature of the input, i.e. the biochemical composition, and the working temperature of the digester from which the digestate or inoculum was taken.

[0073] In the case where process 1 is carried out before the construction of the digester and during its sizing, then as for the samples, the working temperature of the pilot digesters from which the digestate was taken or the working temperature for which one wishes to have the data or operate the sized digester is chosen.

[0074] The determination method 1 then comprises a determination step 4 from said analyses of the analysis step 3 of a relationship between the mass proportions of additive added and the kinetics of methane production.

[0075] For this, the kinetics of methane production is studied as a function of the percentage of additive added to the enriched input by plotting, for example, a graph and extrapolating the curve obtained as shown in [Fig.2] which corresponds to a graph of methane production as a function of time following the percentage of biochar added at a temperature fixed at 42.5°C.

[0076] Preferably, the methane production kinetics has two possible types of relationship: an exponential relationship or a linear relationship.

[0077] The exponential relationship means that the digestate is not acclimatized to the inhibiting conditions. Thus, methane production shows an acclimatization phase also called the lag phase of the microorganisms to the conditions and then an exponential phase during which the production of methane is due to the exponential development of the acclimatized microorganisms.

[0078] On the contrary, the linear relationship means that the digestate is active and acclimatized to the inhibiting conditions. The microorganisms present are, therefore, already capable of consuming propionic acid, and thus, they are not limited by the amount of substrate which justifies the linear production of methane until the concentration of the other compound chosen from the products of acidogenesis becomes limiting. The curve representing this relationship will then present a linear part until reaching a plateau.

[0079] Then, depending on the determined methane production relationship, the method comprises a step 5 of predicting a parameter representative of the maximum activity of the microorganisms depending on said determined relationship. Depending on the determined relationship, the parameter representative of the maximum methane activity to be calculated is chosen from a specific growth rate of the microorganisms in the digestate or a maximum methane production rate.

[0080] Indeed, if the relationship determined previously is exponential then the parameter to be calculated is the specific growth rate of the microorganisms in the digestate. The specific growth rate makes it possible to express the multiplication rate of the bacteria present in the biomass. It is predicted either by taking the best determined value or by calculating it from a mathematical relationship determined as a function of the time derivative of the production curve expressed in logarithm on a part where the curve is linear.

[0081] [Fig.3] shows a graph representing the logarithm of the quantity of methane produced as a function of time expressed in days. In [Fig.3], the highlighted part corresponds to the linear part which will be used to calculate the specific growth rate.

[0082] [Fig.4] presents a graph representing the different specific growth rates calculated for different doses of trace element, with or without the addition of 1% biochar and different digestion temperatures.

[0083] If the previously determined relationship is linear then the parameter to be calculated is the maximum methane production rate of the process. It is predicted either by taking the best determined value or by calculating it from a mathematical relationship determined as a function of the derivative of the linear part of the methane production curve as a function of time.

[0084] Finally, the determination method 1 comprises a final step 6 of determining the mass proportion of additive to be added to the input as a function of the parameter representative of the maximum activity of the predicted microorganisms.

[0085] Whatever the parameter calculated in the previous step 5, the mass proportion of additive to be added is calculated as a function of this but also as a function of the process constraints or the technical-economic constraints, for example the cost of the additive.

[0086] Indeed, if process 1 is carried out for an already existing site then the quantity of additive is calculated according to the constraints of this process but also the choice of additive, its cost or even the maximum flow rate that can be injected into the process.

[0087] On the contrary, if process 1 is carried out during the design stage then it should be calculated according to a predetermined safety margin, the constraints of the site on which the process will be implemented, or even according to technical-economic constraints taking into account for example the materials to be used, the size of the equipment, the cost of the additive, among others.

[0088] Furthermore, in the case where an exponential relationship has been determined during step 4, an optimal strategy can then be defined for digestates which are not suitable for anaerobic digestion comprising high concentrations of ammoniacal nitrogen or for restarting a digester which has undergone an inhibition phenomenon, for example, when an input having a proteinaceous methanization substrate and which can generate high concentrations of ammoniacal nitrogen. A very typical case of digestates not acclimated to ammoniacal nitrogen at high concentrations is digested sewage treatment plant sludge.

[0089] In the case of linear growth, this method 1 can, for example, allow the optimization of the sizing or operation of a methanizer in steady state.

[0090] Control method

[0091] The invention also relates to a method for controlling a mass proportion of additive to be injected into a digester.

[0092] The mass proportion of additive to be injected is first determined using method 1 described above.

[0093] Once the mass proportion is determined, the process then controls the injection of the additive in the digester.

[0094] Determination device

[0095] The invention also relates to a determination device making it possible to implement the different steps of the method for determining a mass proportion of additive to be injected into a digester suitable for producing digestate and biogas.

[0096] The device firstly comprises means for acquiring a portion of one or more samples of the digestate from the digester. These means may be automated or manual, in which case the input will be taken by an operator. The sampling means are preferably at the level of the recirculation or extraction pipe of the digester.

[0097] The device then comprises means for enriching each acquired sample comprising means for adding a first concentration of ammoniacal nitrogen and a second concentration of another compound chosen from the products of acidogenesis. These means can be automated and are then used on the production line but preferably they are carried out manually by an operator in the laboratory. The addition and enrichment means are then materials usually used in the laboratory.

[0098] The device further comprises analysis means comprising means for adding to each enriched sample a mass proportion of additive, and means for measuring methane production kinetics. Each sample comprises a mass proportion of additive different from the others.

[0099] As for the enrichment means, these means can be automated and are then used on the production line but preferably they are carried out manually by an operator in the laboratory. The means for adding the additive are then materials usually used in the laboratory. The means for measuring the kinetics of methane production are, for example, flow meters or barometers installed at the outlet of a sealed container in which the digestion of another compound chosen from the products of acidogenesis by the digestate samples in the presence of the inhibitors takes place.

[0100] The device also comprises means for determining a relationship between the mass proportions of additive and the kinetics of methane production, as well as means for predicting a parameter representative of the maximum activity of the microorganisms as a function of the determined relationship, and means for determining the mass proportion of additive to be added as a function of the parameter representative of the calculated maximum methane activity.

[0101] For the implementation of these latter means or the preceding automated means, the device comprises a computer, or more generally at least one processor or any other type of digital calculator. The device may also comprise a plurality of separate digital processors or computers, forming different means of the device, cooperating with each other. The device may be implemented in real time or there may be a delay between the different stages of this device.

[0102] Control device

[0103] The invention finally relates to a device for controlling a mass proportion of additive to be injected into a digester adapted to produce a digestate and biogas, containing methane, comprising the determination device described above as well as means for injecting the determined mass proportion of additive into a digester. The injection means may, for example, be openings which may be present throughout the digestion circuit, whether at the level of the substrate recirculation pipes, the digester input or in the digester.

Claims

Claims

1. Method for determining (1) a mass proportion of additive to be injected into an anaerobic digester adapted to produce a digestate and biogas containing methane, from an input comprising organic matter, said additive being intended to promote at least one reaction of degradation of the organic matter by microorganisms in said digester, said method comprising: - a step of acquiring (2) one or more representative samples of said digestate from the digester, each sample being enriched by a first concentration of a compound inhibiting anaerobic digestion and by a second concentration of another compound chosen from the products of acidogenesis;- an analysis step (3), during which, for each acquired sample, a mass proportion of said additive is added to the enriched sample, and methane production kinetics are measured, the mass proportions of additive being distinct for each sample; - a step (4) of determining from said analyses a relationship between the mass proportions of additive added and the methane production kinetics; - a step (5) of predicting a parameter representative of the maximum activity of the microorganisms as a function of said determined relationship, and - a step (6) of determining the mass proportion of additive to be added to said input as a function of the predicted parameter representative of the maximum activity of the microorganisms.;

2. Determination method (1) according to claim 1, characterized in that the other compound chosen from the products of acidogenesis is propionic acid.

3. Determination method (1) according to claim 1 or 2, characterized in that the additive is chosen from biochar, iron oxide, activated carbon and / or a trace element such as iron, nickel, cobalt, molybdenum, selenium, tungsten, zinc, and tin.

4. Determination method (1) according to claim 3, characterized in that during the analysis step (3), the mass proportion of additive is between 1 g / kg and 50 g / kg of input organic matter inclusive for biochar, iron oxide or activated carbon or 0.01 to 10 mg / kg of input organic matter for one or more oligo- elements individually or in mixture.

5. Determination method (1) according to any one of claims 1 to 4, characterized in that during the enrichment of the sample, the inhibiting compound is chosen from ammoniacal nitrogen, a heavy metal, a chlorophenol, a halogenated aliphatic compound, a pesticide, an antibiotic, and a lignocellulose hydrolyzate.

6. Determination method (1) according to claim 5, characterized in that the inhibiting compound is ammoniacal nitrogen at a first concentration of at least 1 g / L.

7. Determination method (1) according to any one of claims 1 to 6, characterized in that during the enrichment of the sample, the second concentration of another compound chosen from the products of acidogenesis is at least 1 g / L.

8. Determination method (1) according to any one of claims 1 to 7, characterized in that the parameter representative of the maximum activity of the microorganisms is chosen from a specific growth rate of the microorganisms in the digestate and / or a maximum rate of methane production.

9. Method for controlling a mass proportion of additive to be injected into a digester adapted to produce digestate and biogas, containing methane, in which: - a mass proportion of additive to be injected is determined by the determination method (1) according to any one of the preceding claims; and, - the determined mass proportion of additive is injected into the digester.

10. Device for determining a mass proportion of additive to be injected into an anaerobic digester adapted to produce a digestate and biogas containing methane, from an input comprising organic matter, said additive being intended to promote at least one reaction of degradation of the organic matter by microorganisms in said digester, said device being characterized in that it comprises: - means for acquiring one or more representative samples of said digestate from the digester and means for enriching each sample in a first concentration of an anaerobic digestion inhibitor compound and in a second concentration of another compound chosen from the products of acidogenesis; - means of analysis of each sample acquired, comprising means of addition, to the enriched sample, of a mass proportion of said additive, and means of measuring methane production kinetics; - means of determining a relationship between the mass proportions of additive and the kinetics of methane production; - means for predicting a parameter representative of the maximum activity of microorganisms as a function of said determined relationship, and, - means of determining the mass proportion of additive to be added to said input as a function of the parameter representative of the maximum activity of the predicted microorganisms.

11. Device for controlling a mass proportion of additive to be injected into a digester adapted to produce digestate and biogas, containing methane, comprising: - the determination device according to claim 10; and, - means of injecting the determined mass proportion of additive into the digester.

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