Method for calculating an operating parameter of a digester in the presence of at least one inhibitor

Abstract

The invention relates to a method (1) for calculating an operating parameter of a digester suitable for producing a digestate and biogas, containing methane, the method comprising the following steps: - a step (2) of defining a concentration range of an input of the digester and an operating temperature range of the operation; - a step (3) of preliminarily estimating an intermediate concentration; - a step (4) of determining the pH within the digester; - a step (5) of estimating a concentration of at least one inhibitor compound present within the digester; - a step (6) of identifying one or more microorganisms exhibiting limiting kinetics present in the digester; - a step (7) of predicting the maximum growth rate of the one or more determined microorganisms; - a step (8) of identifying the maximum admissible load in the digester; and - a step (9) of calculating the operating parameter of the digester according to the identified maximum admissible load.

Description

[0001] Description

[0002] METHOD FOR CALCULATING AN OPERATING PARAMETER OF A DIGESTOR IN THE PRESENCE OF AT LEAST ONE INHIBITOR

[0003] The invention relates to the field of digesters, also called biogas reactors or methanizers.

[0004] More particularly, the invention relates to a method for calculating an operating parameter of a digester.

[0005] The purpose of a digester is to produce biogas through anaerobic digestion.

[0006] Anaerobic digestion is a cascade of biochemical reactions that convert organic matter in the digester into biogas, which is primarily a mixture of carbon dioxide and methane. The remaining material is called digestate.

[0007] This process is inherently complex because:

[0008] - each degradation step is carried out by distinct groups of microorganisms, each having their own kinetics, optimal growth conditions and specific inhibitory compounds;

[0009] - these groups of microorganisms interact with each other, which can result, for example, in competition or syntrophy phenomena;

[0010] - the operating conditions of the process, such as the feeding method as well as the nature of the input or even the temperature, strongly influence the kinetics of these groups of microorganisms.

[0011] This complexity makes it relatively difficult to size reactors and monitor this process.

[0012] In addition, inhibitory compounds frequently present in anaerobic digestion such as ammonia and hydrogen sulfide particularly affect certain groups of microorganisms, leading to a significant modification of the methane productivity of the process.

[0013] The management of these compounds is therefore crucial for the proper functioning of anaerobic digestion processes, particularly on sites treating inputs rich in nitrogen and sulfur.

[0014] Currently, several methods of managing these compounds and the resulting drop in process productivity are used, these methods are:

[0015] - reducing the feed rate based on a biogas or digestate monitoring parameter such as organic acid concentration. This involves reducing the digester input load when the monitoring parameter indicates potential inhibition and thus increasing the hydraulic residence time of the process;

[0016] - reducing the concentration of the digester input by diluting with water, for example. This method consists of adjusting the nitrogen and sulfur concentration at the digester input based on predefined thresholds;

[0017] - adjusting the quality of the digester input by adjusting the quantities of the different available inputs in order to feed the digester with a mixture without excess nitrogen and / or sulfur, based on predefined thresholds. This method is carried out in cases of co-digestion; and,

[0018] - the addition of reagents within the digester to regulate physicochemical and / or biological phenomena. For example, reagents containing iron can be added to precipitate the sulfur present in the digester and limit the concentration of hydrogen sulfide.

[0019] However, among all the methods currently used, none takes temperature as a variable for adjusting the digester influencing the inhibitors and consequently the growth of microorganisms.

[0020] In fact, during the sizing and construction of the digester, the temperatures are most often fixed a priori and are generally not modified during operation.

[0021] However, the optimal temperature for the growth of microorganisms during anaerobic digestion is not necessarily the same in the presence or absence of inhibitory compounds. Thus, there is a need for a method for identifying the optimal temperatures of an anaerobic digestion process depending on the quantity of inhibitors and microorganisms present in the medium in order to carry out optimal sizing and control of the process.

[0022] A method is proposed for calculating an operating parameter of a digester suitable for producing digestate and biogas, containing methane, said method comprising the following steps:

[0023] - A step of defining a concentration range of a digester input and a temperature range for operating the operation;

[0024] - A step of preliminary estimation of an intermediate concentration based on the defined concentration range of the digester input; said estimated intermediate concentration being defined as being the concentration of an inhibitory compound or the sum of the concentrations of several compounds including at least one inhibitory compound;

[0025] - A step of determining the pH within the digester over the entire temperature range defined during the definition step, and as a function of the intermediate concentration estimated during the preliminary estimation step;

[0026] - A step of estimating a concentration of at least one inhibitory compound present within the digester over the entire temperature range defined during the definition step, and as a function of the pH determined within the digester and the intermediate concentration estimated during the preliminary estimation step; - A step of identifying one or more microorganisms exhibiting limiting kinetics present in the digester;

[0027] - A step of predicting the maximum growth rate of the determined microorganism(s) over the entire temperature range defined during the definition step and the concentration of at least one inhibitory compound estimated during the estimation step;

[0028] - A step of identifying the maximum permissible load in the digester based on the predicted maximum growth rate, the microorganism(s) identified, the operating temperature range defined during the definition step and the concentration range of a defined digester input; and

[0029] - A step of calculating said operating parameter of the digester based on the maximum admissible load identified.

[0030] One advantage is thus to propose a method for calculating the operation of a digester taking into account the influence of one or more inhibitors.

[0031] Advantageously and limitingly, the operating temperature range of the operation is between 10 and 70°C.

[0032] An advantage is that the temperature range is large enough to cover a wide range of digester operating temperatures.

[0033] Advantageously and in a limiting manner, when the concentration of the digester input is imposed, the concentration range of the input is reduced to the imposed input concentration.

[0034] An advantage is to perform the calculation taking into account the operating conditions of the digester.

[0035] An advantage is to perform the calculation in the case where at least one inhibitory compound present in the digester is ammonia (NH3) and / or ammonium ion (NH4 + ).

[0036] An advantage is to perform the calculation taking into account at least one known inhibitory compound often present in a digester.

[0037] An advantage is to perform the calculation in the case where at least one inhibitory compound present in the digester is hydrogen sulfide (H2S) and / or hydrogen sulfide ion (HS ). An advantage is to perform the calculation taking into account at least one known inhibitory compound often present in a digester.

[0038] An advantage is to perform the calculation in the case where at least one inhibitory compound present in the digester is a heavy metal.

[0039] An advantage is to perform the calculation taking into account at least one known inhibitory compound often present in a digester.

[0040] The invention also relates to a device for calculating an operating parameter of a digester suitable for producing digestate and biogas, containing methane, in the presence of at least one inhibitor, said calculation device comprising: - Means for defining a concentration range of an input to the digester and an operating temperature range of the operation;

[0041] - Means for preliminary estimation of an intermediate concentration as a function of the concentration range of the input of the defined digester; said estimated intermediate concentration being defined as being the concentration of an inhibitory compound or the sum of the concentrations of several compounds including at least one inhibitory compound;

[0042] - Means for determining the pH within the digester over the entire temperature range defined during the definition stage, and as a function of the intermediate concentration estimated during the preliminary estimation stage;

[0043] - A step of estimating a concentration of at least one inhibitory compound present within the digester over the entire temperature range defined during the definition step, and as a function of the pH determined within the digester and the intermediate concentration estimated during the preliminary estimation step;

[0044] - Means of identifying one or more microorganisms with limiting kinetics present in the digester,

[0045] - Means for predicting the maximum growth rate of the determined microorganism(s) over the entire temperature range defined during the definition step and the concentration of at least one inhibitory compound estimated during the estimation step;

[0046] - Means for identifying the maximum permissible load in the digester based on the predicted maximum growth rate, the identified microorganism(s), the operating temperature range defined during the definition step and the concentration range of a defined digester input; and

[0047] - Means of calculating an operating parameter of the digester based on the maximum admissible load identified.

[0048] The device according to the invention here comprises a computer, or more generally at least one processor or any other type of digital calculator.

[0049] The device may also comprise a plurality of separate digital processors or computers, forming different means of the device, cooperating with each other. Other features and advantages of the invention will become apparent upon 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:

[0050] - [Fig. 1] is a flowchart of the calculation method according to the invention;

[0051] - [Fig. 2] is a curve illustrating the empirical relationship between pH and total ammoniacal nitrogen present in a digester in the case of an implementation of the invention;

[0052] - [Fig. 3] is a heat map illustrating the relationship between the concentration of NH3 in the digester (color) as a function of the dryness of the feed sludge (abscissa) and the operating temperature (ordinate) in the case of an implementation of the invention;

[0053] - [Fig. 4] is a heat map illustrating the relationship between the growth rate of the kinetically limiting microorganism as a function of the dryness of the feed sludge and the operating temperature in the case of an implementation of the invention;

[0054] - [Fig. 5] is a heat map illustrating the relationship between the maximum load applicable to the digester as a function of the dryness of the feed sludge and the operating temperature in the case of an implementation of the invention;

[0055] The calculation method according to the invention aims to calculate an operating parameter of a digester, fed by an input such as sludge from a treatment plant and producing at the output a digestate and biogas composed essentially of methane and carbon dioxide.

[0056] The calculation method according to the invention is also applicable for the calculation of an operating parameter of a biological process such as fermentation by microbial communities.

[0057] Each digester, due to the composition of the input or the anaerobic reactions involved, has different performances and therefore different optimal operating conditions.

[0058] By calculating the optimal operating conditions, the process can be designed and / or operated in such a way as to obtain maximum biogas yield and productivity.

[0059] With reference to figure 1, the calculation method 1 comprises a first step 2 of defining a concentration range of an input to the digester and an operating temperature range of the operation.

[0060] The definition of a digester input concentration range depends on the site's operational constraints. The dry matter input concentration, also called the digester input dryness, is measured in terms of the percentage of dry matter, which is an indicator of the dewatering of the sludge used as a digester input.

[0061] The percentage of dry matter is the ratio between the mass of dry matter and the mass of raw material. For example, digester input sludge can contain between 0% DM and 25% DM of dry matter.

[0062] The definition of the concentration range depends on the operating constraints of the site:

[0063] - if the site exists and is in operation, the concentration range corresponds to the working concentration range of the input at the output of the pretreatment process.

[0064] - if the site exists and is going to be started up or if a new input is used then the concentration range will be chosen according to its characterization. The range will be between its maximum concentration and below.

[0065] - if the calculation is carried out during site design then the chosen concentration range could be wider while being limited to a hypothetical value of a maximum concentration of the input.

[0066] In another embodiment, if a concentration of the digester input is imposed in the process then the concentration range will be reduced to the imposed input concentration.

[0067] As for the temperature range to be defined, it can cover different operating temperature zones. The so-called psychropile zone with a temperature between 0°C and 20°C, the so-called mesophilic zone with a temperature between 20°C and 40°C, the so-called thermophilic zone with a temperature between 40°C and 60°C and the so-called hyper-thermophilic zone with a temperature between 60°C and 80°C.

[0068] In the same way as for the definition of the concentration range, the definition of the operating temperature range of the digester depends on the operating constraints of the site:

[0069] - if the site exists and is in operation, the temperature range corresponds to the working temperature range of the process.

[0070] - if the site exists and is going to be started up or if a new input is used then the concentration range will be chosen according to the temperature of the input at the outlet of the pretreatment process or a predetermined working temperature range.

[0071] - if the calculation is carried out during the site design then the chosen temperature range can be wider while being limited to a hypothetical value of a predetermined maximum temperature.

[0072] In another embodiment, the operating temperature range of the method is between 10 and 70°C.

[0073] The calculation method 1 then comprises a second preliminary estimation step 3 of an intermediate concentration as a function of the defined digester input concentration range.

[0074] In a first embodiment, the intermediate concentration corresponds to the concentration of an inhibitor compound.

[0075] Inhibitory compounds are compounds that affect certain groups of microorganisms present within the digester. Thus, if the concentration of these compounds increases, the productivity of the digester will greatly decrease.

[0076] The most common inhibitory compounds are hydrogen sulfide (H2S) or hydrogen sulfide ion (HS), but also ammonia (NH3) or ammonium ion (NH4). Other inhibitory compounds may be present in the digester, such as heavy metals.

[0077] Examples include the following publications which present inhibitory compounds that may be present in the digester:

[0078] - Ying Jiang, et al. Ammonia inhibition and toxicity in anaerobic digestion: A critical review. Journal of Water Process Engineering, 2019.

[0079] - Qian Guoa, et al. Heavy metals interact with the microbial community and affect biogas production in anaerobic digestion: A review. Journal of Environmental Management, 2019.

[0080] - Hang P. Vu, et al. Hydrogen sulfide management in anaerobic digestion: A critical review on input control, process regulation, and post-treatment. Bioresource Technology, 2021. For example, if we take a heavy metal such as mercury or lead, the intermediate concentration is calculated for this inhibitory compound based on the defined digester input concentration range.

[0081] However, the intermediate concentration does not correspond to the actual concentration of this compound in the digester because certain parameters such as pH for example influence the concentration of this inhibitory compound. There is therefore a variation between the concentration calculable by the concentration of the digester input and the concentration of this compound in the digester.

[0082] Thus, the intermediate concentration calculated in this embodiment will be used in the next step to determine the pH within the digester.

[0083] In a second embodiment, the intermediate concentration corresponds to the sum of the concentrations of several compounds including at least one inhibitory compound.

[0084] Indeed, the concentration of certain inhibitory compounds cannot be calculated directly with the concentration of the digester input but requires other parameters, notably the pH. This is particularly the case for ammonia (NH3) or the ammonium ion (NH4 + ) For example.

[0085] Thus, if we take the example of ammonia (NH3), we estimate, during this preliminary estimation step 3, the concentration of total ammoniacal nitrogen (N-NH4) from the concentration of the input. The estimated total ammoniacal nitrogen concentration will be used during the next step to determine the pH within the digester.

[0086] The calculation method 1 thus comprises a third step 4 of determining the pH within the digester over the entire temperature range defined during the definition step, and as a function of the intermediate concentration estimated during the preliminary estimation step.

[0087] The purpose of this step is to determine the pH that allows for balancing all the acid-base reactions that can take place within the digester. This is why at least one of the compounds whose intermediate concentration is estimated belongs to an acid-base pair regardless of the method used.

[0088] The pH within the digester is not necessarily homogeneous. The skilled person will therefore be free to assume an infinitely mixed reactor for a homogeneous pH or, for example, the assumption of a plug-flow reactor for an evolving pH.

[0089] The determination of pH can be carried out from charts produced from experimental measurements or found in the literature.

[0090] Alternatively, it can be determined by calculation either by performing simplified calculations by making several assumptions or by using powerful calculation software taking into account several factors such as the precipitation of certain compounds for example. One can cite as an example the following book which presents a computer program designed to perform a wide variety of aqueous geochemical calculations and implementing several types of aqueous models:

[0091] Parkhurst, DL, and Appela, CAJ Description of input and examples for PHREEQC version 3 — A computer program for speciation, batch-reaction, one-dimensional transport, and inverse geochemical calculations. US Geological Survey Techniques and Methods, 2013.

[0092] However, the person skilled in the art will be free to select the determination method that suits him.

[0093] The calculation method 1 then comprises a fourth step 5 of estimating a concentration of at least one inhibitory compound present within the digester over the entire temperature range defined during the definition step, and as a function of the pH determined within the digester and the intermediate concentration estimated during the preliminary estimation step.

[0094] Thus, if we take ammonia (NH3) as an example, the pH will make it possible to determine the concentration of NH3 in relation to the concentration of total ammoniacal nitrogen, i.e. the proportion of NH3 in relation to the total ammoniacal nitrogen present in the digester.

[0095] As an example, the following publication can be cited, which presents examples of the range of ammonia concentrations in a digester. The ammonia concentration can therefore be between 0 mg / L and 1500 mg / L:

[0096] G. Capson-Tojo, R. Moscoviz, S. Astals, Robles, J.-P. Steyer. Unraveling the literature chaos around free ammonia inhibition in anaerobic digestion. Renewable and Sustainable Energy Reviews, 2020.

[0097] The calculation method 1 then comprises a fifth step 6 of identifying one or more microorganisms exhibiting limiting kinetics present in the digester. In the digester, several species of microorganisms may be present such as hydrogenotrophic methanogenic archaea, acetoclastic methanogenic archaea or even syntrophic bacteria oxidizing propionate or acetate.

[0098] The species of microorganisms growing in the digester do not have the same growth rate. Thus, some species will exhibit limiting kinetics because they will have a slower growth rate than certain other species, thus limiting the speed of the overall reaction of the digester.

[0099] The aim of this step is therefore to identify the species(s) of microorganism(s) presenting limiting kinetics for the calculation of an operating parameter since it is these species which will limit the reaction.

[0100] The identification of the microorganism(s) exhibiting limiting kinetics can be carried out in several ways, either from databases created or found in the literature, or by experiment using data determined in the previous stages.

[0101] Experience means that after several applications of this step, the person skilled in the art will have sufficient data and experience to choose the limiting microorganism(s) based on the various data from the previous steps.

[0102] An example of microorganisms exhibiting limiting kinetics is the bacterium Methanosarcina barkeri, which is cited in particular in the following article:

[0103] Gloria M. Maestrojuan and David R. Boone. Characterization of Methanosarcina barkeri MST and 227, Methanosarcina mazei S-6T, and Methanosarcina vacuolata Z-761. International Journal of Systematic Bacteriology, 1991.

[0104] Then, the calculation method comprises a sixth step 7 of prediction of the maximum growth rate of the limiting microorganism(s) determined over the entire temperature range defined during the definition step and of the concentration of at least one inhibitory compound estimated during the estimation step.

[0105] Indeed, in the digester, the growth of microorganisms depends essentially on the temperature, the pH and the concentration of inhibitor compound. These factors will more or less slow down or accelerate the reaction. It is therefore necessary to take into account the dependence of the growth of microorganisms on these factors in order to choose the optimal operating conditions for the process.

[0106] The dependence of the growth rate on these factors can be modeled by mathematical models. They are widely described in the literature for many known microorganisms present in digesters.

[0107] We can cite for example the following article: I. Angelidaki, L. Ellegaard, and BK Ahring. A Mathematical Model for Dynamic Simulation of Anaerobic Digestion of Complex Substrates: Focusing on Ammonia Inhibition. Biotechnology and Bioengineering, 1993.

[0108] This paper presents a mathematical model of the growth rate of 4 groups of microorganisms (glucose-fermenting acidogens, propionate-degrading acetogens, butyrate-degrading acetogens, and acetic acid methanogens) as a function of pH, temperature, and ammonia inhibition.

[0109] The following article can also be cited as an example: Batstone, DJ, Keller, J., Angelidaki, L, Kalyuzhnyi, SV, Pavlostathis, SG, Rozzi, A., Sanders, WTM, Siegrist, H., Vavilin, VA., 2002. The IWA Anaerobic Digestion Model No 1 (ADM1). Water Science and Technology, 2002.

[0110] This article, for its part, introduces the ADM1 model, an international reference in the field, which is a dynamic model allowing the simulation of the phenomena governing the different stages of anaerobic digestion by integrating a large number of factors having an influence on the different kinetics, in particular the growth rate of microorganisms.

[0111] Once the growth rates have been determined based on the different factors, the maximum growth rate of the limiting microorganism(s) identified in the previous step in the digester is predicted by studying this function and identifying its optimum.

[0112] The calculation method comprises a seventh step 8 of identifying the maximum admissible load in the digester as a function of the predicted maximum growth rate of the identified microorganism(s), the operating temperature range defined during the definition step and the concentration range of a determined methanization substrate.

[0113] The maximum permissible load in the digester can be identified based on the various parameters already known in the digester.

[0114] For example, for an infinitely mixed continuous reactor, the maximum growth rate of a microorganism can be directly related to the dilution rate of the reactor. The maximum permissible load of the digester can then be identified as a function of the dryness of the digester input and the operating temperature.

[0115] Finally, the calculation method 1 includes a final calculation step 9 of the operating parameter of the digester as a function of the identified maximum admissible load. This operating parameter of the process may be the concentration of the input, the residence time or the flow rate of the input in the process or the temperature.

[0116] If calculation method 1 is carried out for an existing site, then the parameter will be chosen according to the constraints of this process. For example, the concentration of the input can be modified by diluting it before entering the reactor.

[0117] If calculation method 1 is carried out during the design stage, then the parameter should be chosen based on a predetermined safety margin, the constraints of the site on which the process will be installed, or according to technical and economic constraints taking into account, for example, the materials to be used and the size of the equipment. The example presented below is an application of the calculation method to the sizing of a digester treating sludge from a sewage treatment plant.

[0118] First, in definition step 1, a concentration range of a digester input between 4 and 8% DM and an operating temperature range of the operation between 30°C and 45°C are defined.

[0119] Then, in the preliminary estimation step 2, for the concentration range defined in step 1, an intermediate concentration is estimated to correspond to the total ammoniacal nitrogen (sum of the concentration in NEE and NEE) between 1.5 and 3 gN.L -1 .

[0120] This concentration was determined based on a nitrogen mineralization potential test for this sludge. The data were taken from the article Bareha et al., Modeling of nitrogen transformation processes in anaerobic digestion. Application to the optimization of digestate recovery, 2018.

[0121] Step 3 of determining the pH within the digester is carried out using a chart shown in Figure 2 which shows the relationship between pH and total ammoniacal nitrogen in a digester. This data is taken from experimental measurements.

[0122] The result of step 4 corresponding to the estimation of the concentration of the inhibitory compound, here ammonia (NEE), is presented in Figure 3 in the form of a heat map of the NEE concentration in the digester as a function of the concentration of the digester input and the operating temperature of the operation. The method for estimating the ammonia concentration is taken from the article Capson-Tojo et al., 2020 cited previously.

[0123] Under these conditions, according to the article Capson-Tojo et al., 2020, the limiting phase is acetoclastic methanogenesis. We can thus identify in step 5, the microorganism Methanosaeta concilii as having limiting kinetics. It is part of the acetoclastic methanogenic archaea which are microorganisms typically present in a wastewater treatment plant sludge digester.

[0124] The description of this microorganism is made in the article (Patel and Sprott, 1990), this allows to carry out step 6 of the calculation process. We can then know the dependence of its maximum growth rate as a function of temperature and pH. In addition, a dependence of the growth rate as a function of the NH3 concentration can be represented by a non-competitive inhibition function, as proposed in the ADM1 model (Batstone et al., 2002), using an IC50 value as reported in the literature (Capson-Tojo et al., 2020).

[0125] The maximum growth rate of this microorganism, shown in Figure 4, can then be deduced as a function of the dryness of the digester feed sludge and the temperature.

[0126] Assuming the reactor is a continuously stirred tank, the growth rate of this microorganism is related to the dilution rate of the reactor. Thus, the maximum permissible load is identified, step 7, based on the concentration of the digester input and the operating temperature of the operation. The maximum permissible load is shown in Figure 5.

[0127] Finally, since microorganisms never operate at their maximum growth rate in practice, a safety factor must be applied to the sizing of the digester. By taking a safety factor of 3, we then obtain an optimal load to be applied to the digester of 2.15 kgMS / m3 / d obtained for a working temperature of 35°C and an input concentration of 4.8%MS.

Claims

Claims) A computer-implemented method for calculating an operating parameter of a digester adapted to produce digestate and biogas containing methane, said method comprising the following steps: - A step of defining a concentration range for an input to the digester and a temperature range for the operation of the process; - A preliminary estimation step of an intermediate concentration based on the defined concentration range of the digester input; said estimated intermediate concentration being defined as the concentration of an inhibitory compound or the sum of the concentrations of several compounds, including at least one inhibitory compound; - A step to determine the pH within the digester over the entire temperature range defined during the definition step, and according to the estimated intermediate concentration; - A step of estimating the concentration of at least one inhibitory compound present within the digester over the entire temperature range defined during the definition step, and as a function of the pH determined within the digester and the intermediate concentration estimated during the preliminary estimation step; - A step to identify one or more microorganisms with limiting kinetics present in the digester; - A step of predicting the maximum growth rate of the microorganism(s) determined over the entire temperature range defined during the definition step and the concentration of at least one inhibitory compound estimated during the estimation step; - A step to identify the maximum permissible load in the digester based on the predicted maximum growth rate of the identified microorganism(s), the operating temperature range defined during the definition step, and the concentration range of a defined digester input; and - A calculation step for said digester operating parameter as a function of the identified maximum permissible load. ) Calculation method according to claim 1 characterized in that the operating temperature range is between 10 and 70°C. ) Calculation method according to claim 1 or 2, characterized in that when the concentration of the digester input is imposed, the input concentration range is reduced to the imposed input concentration. ) Calculation method according to any one of claims 1 to 3, characterized in that at least one inhibitory compound present in the digester is ammonia (NH3) and / or the ammonium ion (NH4 + ) A calculation method according to any one of claims 1 to 3, characterized in that at least one inhibitory compound present in the digester is hydrogen sulfide (H2S) and / or the hydrogen sulfide ion (HS). ) A calculation method according to any one of claims 1 to 3, characterized in that at least one inhibitory compound is a heavy metal. ) A device for calculating an operating parameter of a digester in the presence of an inhibitor suitable for producing digestate and biogas containing methane, said calculation device comprising: - Means of defining a concentration range for an input to the digester and a temperature range for the operation of the process; - Means of preliminary estimation of an intermediate concentration as a function of the concentration range of the input of the defined digester; said estimated intermediate concentration being defined as the concentration of an inhibitory compound or the sum of the concentrations of several compounds of which at least one is an inhibitory compound; - Means of determining the pH within the digester over the entire temperature range defined during the definition stage, and according to the intermediate concentration estimated during the preliminary estimation stage; - Means of estimating the concentration of at least one inhibitory compound present within the digester over the entire temperature range defined during the definition step, and as a function of the pH determined within the digester and the intermediate concentration estimated during the preliminary estimation step; - Means of identifying one or more microorganisms with limiting kinetics present in the digester, - Means of predicting the maximum growth rate of the microorganism(s) determined over the entire temperature range defined during the definition step and the concentration of at least one inhibitory compound estimated during the estimation step; - Means of identifying the maximum permissible load in the digester based on the predicted maximum growth rate of the identified microorganism(s), the operating temperature range defined during the definition step, and the concentration range of a defined digester input; and - Means of calculating a digester operating parameter as a function of the maximum permissible load identified.

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