Use of magnesium hydroxide to accelerate biogas production kinetics in an anaerobic digester

Abstract

Use of magnesium hydroxide to accelerate biogas production kinetics in an anaerobic digester The present invention relates to the use of magnesium hydroxide to accelerate biogas production kinetics in an anaerobic digester for a given incoming organic matter.

Description

Title of the invention: Use of magnesium hydroxide to accelerate the kinetics of biogas production in an anaerobic digester technical field

[0001] The present invention relates to the field of anaerobic digestion (methanation) of fermentable (digestible) materials for the quantitative production of biogas and / or the reduction of carbon pollution in agricultural inputs, municipal or industrial effluents, and waste sources. It further relates to a magnesium-based additive formulation that accelerates the kinetics of the methanation reaction for the same incoming organic feedstock, thereby enabling faster processing of the organic feedstock and thus the production of more biogas over time in a methanizer of a given size.

[0002] The present invention is therefore aimed at actors in the technical sector "Methanization" whose potential users are part of the following sectors: agriculture, industry, household waste and municipal wastewater treatment plant.

[0003] More particularly, it is intended for operators of a dry or liquid methanation unit, equipped with a continuous perfectly stirred reactor (CSTR), a plug flow reactor (PWR), a fluidized bed sludge (UASB) or a granular sludge bed (EGSB), for the purpose of biogas production, even more particularly when this biogas is subsequently directly injected into the network or recovered as electricity and heat by cogeneration and contributes to creating a source of income for the unit in question. Previous technique

[0004] To meet the environmental and energy challenges of the current situation, anaerobic digestion is an interesting and promising waste treatment technique since it allows the combination of "treatment of carbon pollution" and "energy production".

[0005] However, the sector also faces technical challenges that can destabilize the economic viability of a project: - Methanizers operate empirically, with digestion conditions that are complicated to find because there are large variations: inputs (mainly), seasonality, conditions from one farm to another. - Methanizers must operate under degraded conditions to meet feeding schedules on the one hand and biogas production targets on the other, inducing potential stress on microorganisms and therefore an inevitable loss of potential production. - A methanizer does not convert all of the available carbon into CH4. Therefore, there is a loss of productivity and a reduced environmental and financial benefit.

[0006] To date, one of the major technical problems facing the sector is therefore the low yield of a unit in relation to the total input charge due to the excessive time required to use the methanogenic potential of the input charge, i.e. that the kinetics of biogas production are not optimal at the scale of the process.

[0007] Maximizing biogas production for a fixed duration and quantity or installation size of incoming organic matter involves increasing the biogas production kinetics of the inputs considered.

[0008] The state of the art for increasing biogas production reveals several strategies already in place. Among them is co-digestion, which involves establishing input mixing strategies to take advantage of the specific characteristics of each. Livestock effluents (slurry and manure), abundant in agricultural methanization, have a lower methanogenic potential but allow for better pH maintenance in the digestion medium. Plant inputs, on the other hand, promote the healthy development of microbial biomass. These include energy crops (intermediate crops), vegetable residues, green waste, etc. Finally, other types of inputs, such as residues from the agri-food industry, can be used for their particularly high methanogenic potential to rebalance the load so that biogas production targets are met.

[0009] Co-digestion is a particularly important and strategic technique for units that have to process a wide variety of inputs. This is notably the case, for example, for units installed in energy centers that collect substrates from the agri-food sector.

[0010] However, it is not always possible to have a wide variety of inputs available, which may restrict the use of co-digestion, nor to have access to the precise characterization of the inputs (%MS, %MO, BMP, composition) available, which may lead to an increased risk of imbalance if there is antagonism between constituents.

[0011] Another approach to maximizing biogas production is to select and maintain very strict operating conditions in the digester, such as temperature, pH, the ratio between volatile organic acids and buffering capacity (FOS / TAC), residence time, percentage of feedstock, percentage of dry matter (DM), and percentage of organic matter (OM). However, this imposes constraints that are difficult to meet due to the empirical operation of digesters.

[0012] It is also possible to maximize this biogas production by using Physical techniques such as grinding or recirculation are used. However, this requires modifying the digesters and / or using more energy, which is costly and the result is not always up to expectations.

[0013] Finally, chemical additive techniques can be used, primarily for remediation, that is, as a corrective action in case of a problem. For example, iron oxides and hydroxides can be added to the digester to correct a sulfur buildup in the medium, and nutrients such as selenium and other micronutrients can be added to correct the nutrient medium for the bacteria.

[0014] Thus, it is known from application WO2009055793 to use alkaline agents to correct the pH of the digester. This application mentions Mg(OH)2 among the list of said alkaline agents. However, magnesium hydroxide is therefore only used as a pH corrector in digesters experiencing a pH problem.

[0015] The inventors were surprised to discover that magnesium hydroxide, particularly standard magnesium hydroxide, especially in powder form, accelerated the biogas production rate for a given input organic matter. This is quite surprising because the biogas production rate is very different from the methanogenic potential of an input. The methanogenic potential of an input is its intrinsic capacity to produce methane, and increasing this potential allows for the production of more biogas per unit of organic feed. In contrast, the biogas production rate is the rate at which methane is produced from an input, and increasing it allows for the processing of more organic feed—and therefore the production of more biogas—in a digester of a given size over a given period.Thus, an input can have a high methanogenic potential and slow kinetics, and conversely, an input can have rapid kinetics but a low methanogenic potential.

[0016] Furthermore, magnesium hydroxide in powder form offers the additional advantage over an aqueous suspension of being easier to handle, requiring less storage capacity, and not requiring any special or dedicated equipment, particularly if packaged in digestible form which can also be added to the digester. Dosing magnesium hydroxide in powder form is also simplified since it can be directly indexed to the incoming organic matter, and the product simply added to it.

[0017] Furthermore, the magnesium hydroxide according to the invention does not require a high specific surface area, which allows it to be manufactured using a simpler and less expensive process (without the need to calcine magnesium carbonate to MgO, a very emitting CO2) than a magnesium hydroxide with a high specific surface area or even using a natural product.

[0018] In addition, magnesium hydroxide according to the invention makes it possible to improve the conversion of organic carbon from the incoming organic matter into biomethane in the anaerobic digester. Description of the invention

[0019] The present invention therefore relates to the use of magnesium hydroxide to accelerate the kinetics of biogas production in an anaerobic digester for a given incoming organic matter.

[0020] For the purposes of this invention, "incoming organic matter" means the organic matter (OM) or carbonaceous matter constituting the inputs of an anaerobic digester that is capable of degrading into biogas and producing biomethane. The proportion of organic matter is generally measured by loss on ignition at 550°C of the dry matter (i.e., of the input dried at 105°C) according to standard NF EN 15935 dated 2021. Indeed, the input contains water, organic matter, and mineral matter.

[0021] For the purposes of this invention, "input" means any organic biomass intended for use in an anaerobic digester. In particular, it is defined in the decree of November 23, 2011 (amended by the decree of June 24, 2014) establishing the nature of inputs in the production of biomethane for injection into natural gas networks. Advantageously, the input is chosen from industrial waste (such as industrial process wash water, industrial sludge), particularly from the agri-food industry (such as lignocellulosic residues, fats, sludge, biowaste, fruits and vegetables, slaughterhouse waste, etc.), agricultural waste (such as livestock effluents and plant waste, in particular manure, slurry, animal by-products, crop residues), energy crops (such as whole plants, silage, hay, etc.).), urban waste (such as sorted household biowaste, or waste from collective catering, large and medium-sized stores, materials resulting from wastewater treatment (such as sludge, grease, organic liquids)) and their mixtures, in particular among livestock effluents (such as slurry, droppings, manure...), plant inputs, residues from the agri-food industry, sewage sludge and their mixtures, more advantageously among slurry, in particular from dairy cows, silage, in particular maize and / or cover crops, co-products of vegetable processing, co-products of camel processing, sewage sludge and their mixtures. .

[0022] Thus, advantageously, the incoming organic matter is chosen from among the organic matter of industrial waste, agricultural waste, energy crops and their mixtures, in particular among the organic matter of livestock effluents, plant inputs, residues from the agri-food industry, sewage sludge and their mixtures, more advantageously among the organic matter of slurry, silage, co-products of vegetable processing, co-products of camel processing, sewage sludge and their mixtures.

[0023] In the context of the present invention, the terms "between ... and ..." and "in the range of ... to ..." mean that the limits of the range are included.

[0024] For the purposes of the present invention, "accelerating the kinetics of biogas production in the anaerobic digester for a given incoming organic matter" means increasing the kinetics of biomethane production for a given incoming organic matter, particularly under the conditions of Example 3, i.e. increasing the rate at which a given incoming organic matter reaches its methanogenic potential and thus decreasing the time required to reach this methanogenic potential.

[0025] The magnesium hydroxide according to the invention can be in the form of an aqueous suspension or in the form of a powder. Advantageously, the density of the powder is in the range of 0.2 to 0.7 g / cm3, measured according to ASTM D7481-09.

[0026] In a particular embodiment, it is in the form of an aqueous suspension, advantageously obtained by precipitation of magnesium hydroxide in water.

[0027] Advantageously, the solids content of the aqueous magnesium hydroxide suspension according to the invention is at least 40% by mass, advantageously at least 50% by mass, more advantageously at least 53% by mass, relative to the total mass of the suspension.

[0028] In another embodiment, the aqueous suspension of magnesium hydroxide according to the invention comprises water as the sole solvent. It advantageously further comprises at least one dispersant, advantageously selected from the group consisting of homopolymers or copolymers of acrylic acid or methacrylic acid and their salts and mixtures thereof, and lignosulfonates and mixtures thereof, in particular selected from polycarboxylates, polyether polycarboxylates, polyacrylates, polyacrylate copolymers, acrylic and / or methacrylic copolymers, salts (in particular polyacrylate salts) and mixtures thereof, and / or at least one antifoaming agent, advantageously selected from the group consisting of silicone oils (such as polydimethylsiloxanes, in particular those marketed by Kurita or ArrMaz) or organic oils, polyglycols,fatty acid esters or polyesters and their mixtures, said oils or polyglycols being able to contain suspended organic or mineral particles, and / or a non-associative thickener or gelling agent (for example, cellulose derivatives, xanthan gum, alginates, polyvi- alcohols, nylic acid (PVA), polyethylene glycol (PEG) or polyoxyethylene (POE), polyvinylpyrrolidone (PVP) or certain members of the acrylic (co)polymer (ASE) family), alkali salts (e.g., magnesium acetate, potassium nitrate) and / or acid conditioners (e.g., acetic acid, citric acid) or a mixture thereof. In particular, the aqueous suspension comprises at least one dispersant.

[0029] In one embodiment, the viscosity of the aqueous magnesium hydroxide suspension according to the invention, measured at 1.7 s 1 at 20°C with a Brookfield viscometer, is less than 1000 mPa.s, preferably less than 700 mPa.s, in particular less than 300 mPa.s.

[0030] In particular, it may be the aqueous suspension described in the applicant's PCT / FR2022 / 050886 application or marketed by the applicant under the name MH53S.

[0031] In an advantageous embodiment, magnesium hydroxide in the form of an aqueous suspension according to the invention has a purity (on a dry matter basis) of at least 80%, advantageously of at least 90%.

[0032] In another particular embodiment, magnesium hydroxide is in powder form.

[0033] In a particular embodiment of the invention, the moisture content of the magnesium hydroxide powder according to the invention, measured by the gravimetric mass loss method at 105°C, is less than 5%, advantageously less than 1%.

[0034] In one embodiment, the magnesium hydroxide particles according to the invention (from the powder or aqueous suspension) have a volume average size, specifically a volume average diameter, D90 less than 200 pm, preferably less than 100 pm, in particular less than 45 pm, more preferably less than 25 pm, even more preferably less than 15 pm, measured by a laser granulometer, specifically the Mastersizer 2000 from Malvern Instruments, more specifically obtained after suspending the powder and diluting the suspension to 20000th and passing through the granulometer.

[0035] In another embodiment, the magnesium hydroxide particles according to the invention (from the powder or aqueous suspension) have a volume average size, specifically a volume average diameter, D50 less than 40 pm, preferably less than 20 pm, in particular less than 7 pm, measured by a laser particle size analyzer, specifically the Mastersizer 2000 from Malvern Instruments, more specifically obtained after suspending the powder and diluting the suspension to 20000th and passing through the particle size analyzer.

[0036] Advantageously the specific surface area of ​​magnesium hydroxide particles according to the invention (of the powder or aqueous suspension) measured by the multipoint BET method by N2 adsorption, in particular with Micro-meritics Gemini VII equipment, is between 1 and 100 m2 / g, more advantageously between 1 and 50 m2 / g, even more advantageously between 5 and 20 m2 / g, in particular between 15 m2 / g and 10 m2 / g, more particularly 10 m2 / g.

[0037] In an advantageous embodiment, magnesium hydroxide in powder form according to the invention has a purity of at least 80%, advantageously of at least 90%.

[0038] Magnesium hydroxide in powder form may be of natural origin (such as brucite ore) or synthetic and may be commercially available from the applicant.

[0039] Magnesium hydroxide in powder form according to the invention can be packaged in digestible packaging.

[0040] In an advantageous embodiment, the dry matter content of magnesium hydroxide used, in mg / g of input organic matter, is between 3 and 30, advantageously between 3.5 and 15, even more advantageously between 3.5 and 10.

[0041] In an advantageous embodiment, magnesium hydroxide according to the invention, particularly in powder form, further improves the conversion of organic carbon from the incoming organic matter into biomethane in the anaerobic digester.

[0042] For the purposes of this invention, "organic carbon," or "TOCg," means any carbon derived from living organisms. Organic carbon is therefore bound to other carbons or to elements such as hydrogen (H), oxygen (O), nitrogen (N), or phosphorus (P) in organic molecules. It can be measured according to standard NF EN ISO 10694, dated 1995, by dry combustion. The total carbon content can also be measured according to standard NF EN ISO 10694, dated 1995, by dry combustion.

[0043] For the purposes of the present invention, "improving the conversion of organic carbon from incoming organic matter into biomethane" means increasing the methanogenic potential of incoming organic matter in an anaerobic digester, in particular obtaining a gain in methanogenic potential of at least 5% for the incoming organic matter compared to the same incoming organic matter without the addition of magnesium hydroxide according to the invention. The methanogenic potential is measured in normo cubic meters (Nm3) of methane under standard temperature (15°C) and pressure (latm) conditions, relative to the quantity of organic matter (OM in tonnes) initially present in the sample used for the test (NmVtOM), and is evaluated by a biochemical methane potential (BMP) test over a period of 20 days. The methanogenic potential represents the quantity of biogas and The methanogenic potential test determines the maximum biogas production from a biomass sample. This test measures the rate of biogas production (methane, CH4) that can be produced by an input in an anaerobic digester until the cumulative amount of biogas produced stabilizes. The methanogenic potential test determines the maximum biogas production of a biomass sample. During this test, the rate of biogas production (fermentation kinetics) and the composition of the biogas produced (methane, CH4, carbon dioxide, H2S, and O2) are measured. This test can be performed on various biomass samples: livestock effluents (slurry, droppings, manure, etc.), agri-food waste (lignocellulosic residues, fats, sludge, etc.), municipal waste (biowaste, sewage sludge, etc.), energy crops (whole plants, silage, hay, etc.), and any other organic residue or by-product. This test is described in detail in Example 1.For this test, a fixed quantity and composition of substrate (ration) is placed in a reactor in contact with active anaerobic microorganisms (inoculum). In particular, the inoculum contains a consortium of bacteria enabling the digestion of incoming organic carbon under anaerobic conditions such as: - Hydrolytic and fermentative bacteria, the main species of which belong to the genera Clostridium, Bacillus, Ruminococcus, Enterobacteroides, Propionibacterium and Butivibrio. - Acetogenic bacteria, the main species of which are the homoacetogenic bacteria of the genera Clostridium, Acetobacterium, Sporomusa, Acetogenium, Acetoanaerobicum, Pelobacter Butyribacterium, Eubacterium..., the syntrophic bacteria of the genera Syntrophobacterium, Syntrophomonas, Syntrophus... and the sulfate-reducing bacteria of the genera Desulfobacter, Desulfotomaculum, Desulfomonas... - Methanogenic bacteria belonging to the Archaea group, the main species of which are Methanobacterium, Methanobrevibacter, Methanosphaera, Methanolobus, Methanococcus, Methanosarcina, Methanocorpusculum, Methanoculleus, Methanogenium, Methanoplanus, Methanospirillum, Methanococcoides, Methanohalophilus, and Methanohalobium. The medium is maintained under optimal fermentation conditions until the cumulative amount of biogas generated stabilizes. The methanogenic potential is the amount of methane produced.

[0044] In a particular embodiment, the anaerobic digester or methanizer is part of a dry or wet process methanation unit equipped with a continuous perfectly stirred reactor (CSTR), a plug flow reactor (PWR), a fluidized bed reactor (UASB), or a granular sludge bed (EGSB). In particular, the anaerobic digester is intended for the quantitative production of biogas, more specifically said biogas being intended to be injected into the network or used to generate electricity and heat through cogeneration, and / or for reducing carbon pollution in an agricultural input or municipal effluent, for example, from a treatment plant municipal or industrial wastewater treatment, or a source of waste, for example, household waste.

[0045] The present invention will be better understood upon reading the description in the figures and the following examples, which are given by way of illustration. Brief description of the drawings

[0046] [Fig-1] Fig. 1 represents the quantity of methane produced (cumulative volumes in NmVtMO) as a function of time (in days) under the conditions of Example 3 for a given ration (input) not added to magnesium hydroxide according to the invention (control) or added to 125 mg of powdered magnesium hydroxide according to the invention (3.8 mg / g OM) (MHP 125 mg) or 180 mg of liquid magnesium hydroxide according to the invention (5.5 mg / g OM). EXAMPLES

[0047] Example 1: Effect of Mg(OH)2 on the methanogenic potential of a ration derived from agricultural inputs

[0048] The effect of adding magnesium hydroxide on biogas production is evaluated by a biochemical methane potential (BMP) test. This test determines the maximum methane production that can be expected from the methanation of a substrate. This test can be performed on any type of biomass sample, waste, or digestate.

[0049] For this test, a fixed quantity and composition of substrate (ration) is placed in a reactor in contact with active anaerobic microorganisms (inoculum). The medium is maintained under optimal fermentation conditions until the cumulative quantity of biogas generated no longer changes. The methanogenic potential is the quantity of methane produced.

[0050] The equipment used is a laboratory pilot plant consisting of 1000 cm³ tanks, each equipped with a gas outlet and a stirring paddle. All the tanks are independent and positioned in an oven at 42°C for the entire duration of the test. A neutral atmosphere (N₂) is injected beforehand, prior to connection to the reactor, to ensure the anaerobic nature of the reaction.

[0051] The ration used is representative of a methanizer in agricultural operation and consists of the following raw materials: - Dairy cow slurry from a farm; - A 50 / 50 mass mixture of maize silage (freeze-dried and ground) and fresh cover crop silage

[0052] The raw materials used are characterized according to: - The dry matter content (%DM) measured by the difference in mass between the raw material and the raw material after drying in an oven at 105°C; - The volatile dry matter content (%DM) measured by the mass difference between the raw raw material and the raw material after drying at 550°C; - the MO ratio measured by the ratio between %MO and %MS. - Carbon content (%C) measured on raw substrate according to the NF ISO 10694 standard of 1995; - The nitrogen content (%N) measured on raw substrate according to standard NF ISO 13654-1 of 2002 and - the C / N ratio measured by the ratio between %C and %N.

[0053] They have the characteristics indicated in the following table 1:

[0054] [Tables 1] Slurry Silage %MS % 2.50 93.00 ratio MO % 99.10 96.00 %MO % 2.48 89.28 %C total % 0.84 42.69 %N Total % 0.08 0.96 %C / N % 10.5 44.5

[0055] The inoculum is obtained by direct sampling of the digestate from a methanization plant located on the farm from which the slurry used in the ration originates. It has the characteristics indicated in Table 2 below:

[0056] [Tables2] Digestate MS % 5.00 MO % 4.92

[0057] The final formulation is calculated so as to place optimal conditions for biogas generation.

[0058] In some tanks the medium is supplemented with a liquid (MHL) or solid (MHP) magnesium hydroxide.

[0059] The MHL additive (according to the invention) used is an aqueous suspension of magnesium hydroxide in water containing 53% by mass relative to the total mass of the suspension of magnesium hydroxide particles whose purity in Mg(OH)2 is 98%, whose particle size (measured by Malvern Instruments Mastersizer 2000 laser particle size analyzer) is less than 100 pm, and whose Specific Surface Area (SSA measured by multipoint BET method by N2 adsorption on Quantachrome Flowin) is 15 m2 / g.

[0060] The MHP additive (according to the invention) used is a magnesium hydroxide powder whose purity in Mg(OH)2 is 94%, whose particle size (measured by Mastersizer 2000 laser granulometer from Malvem Instruments) is less than 100 pm, and whose Specific Surface Area (SSA measured by multipoint BET method by N2 adsorption on Quantachrome Flowin) is 10 m2 / g.

[0061] They exhibit the characteristics indicated in the following table 3:

[0062] [Tables3] Solids Content Water Purity Mg(OH)2 (solid base) Particles passing 100pm SSA (m2 / g) MHL (liquid) 53% 47% 98% >99% 15 MHP (powder) 100% <1% 94% >99% 10

[0063] Several tanks are used in parallel and arranged as follows: - One tank is left empty, in order to create a blank. - Three tanks, hereafter referred to as control tanks, contain no additives and are loaded as follows: 500 g of digestate, 140 g of slurry and 5 g of silage (50 / 50 maize / CIVE). - Three tanks are treated with liquid magnesium hydroxide (MHL) according to the invention and three tanks are treated with solid magnesium hydroxide (MHP) according to the invention and are loaded in the following manner: 500 g of digestate, 140 g of slurry, 5 g of silage (50 / 50 maize / CIVE) and from 110 to 540 mg (on a dry basis) of additive (MHL or MHP).

[0064] The test is conducted over a period of 20 days. This period is sufficient for the cumulative quantity of biogas to remain constant.

[0065] The biogas produced is collected in bags, allowing the quantity generated to be measured. At the end of the test, the bags are analyzed by gas chromatography (GC) using an Agilent Micro GC system to determine the proportion of the different gases present (CO2, CH4, H2S and O2). The methanogenic potential can thus be determined. It is expressed in normo cubic meters (Nm3) of methane under standard temperature (15°C) and pressure (latm) conditions, relative to the quantity of organic matter initially present in the sample. used for the test (NmVtMO). The values ​​are averaged over the three identical cuvettes.

[0066] The gain in Methane Potential brought about by the use of additives is then expressed as the ratio between the values ​​of the control tanks and the tanks with additives.

[0067] The results for the MHL additive (according to the invention) are summarized in the following Table 4

[0068] [Tables4] Examples Quantity of MHL additive mg (dry basis) Content in mg / g OM Methanogenic potential (Nm3 / t OM) Control Methanogenic potential (Nm3 / t OM) Additive Gain from additive application Ex MHL A 540 16.5 489 537 +9.8% Ex MHL B 110 3.8 567 582 +2.6%

[0069] The results for the MHP additive (according to the invention) are summarized in the following Table 5

[0070] [Tables5] Examples Quantity of MHP additive mg (dry basis) Content in mg / g OM Methanogenic potential (Nm3 / t OM) Control Methanogenic potential (Nm3 / t OM) Additive Gain from additive application Ex MHP A 380 11.5 506 547 +8.1% Ex MHP B 125 3.8 854 905 +6.0%

[0071] It therefore appears that adding magnesium hydroxide in solid form to an agricultural input containing 4.92% organic matter increases its methanogenic potential. Furthermore, additive treatment with magnesium hydroxide powder proves to be as effective as additive treatment with a magnesium hydroxide suspension.

[0072] Furthermore, pH measurements of the medium are carried out at the end of the test. These are summarized in the following Table 6:

[0073] [Tableauxô] Example PH Control PH Additive Ex MHL A 7.90 7.90 Ex MHP A 7.96 7.96 Ex MHL B 8.10 8.10 Ex MHP B 8.12 8.08

[0074] It therefore appears that the addition of magnesium hydroxide does not affect, or does not significantly affect, the pH of the medium, and that the effect of gain in methane is therefore not linked to a mechanism of remediation of a pH that is too low.

[0075] Example 2: Effect of Mg(OH)2 on the methanogenic potential of a mixed ration derived from industrial and agricultural waste.

[0076] In this example, we seek to evaluate the repeatability of the effect observed in example 1 on a different formulation.

[0077] The material used is the same as in example 1.

[0078] The feed ration used this time comes from an industrial methanization unit that processes 60,000 tonnes of organic matter from various activities in the area: co-products of vegetable processing, co-products of camellia processing, sewage sludge, etc. The so-called "animal" inputs underwent a heat treatment for sanitization to eliminate any potential pathogens. The animal and plant inputs were then finely ground and mixed. They have the characteristics shown in Table 7 below:

[0079] [Tables7] Ration %MS % 13.9 ratio MO % 98 %MO % 13.7 %C total % 8.64 %N Total % 0.69 %C / N % 12.5

[0080] The inoculum is obtained by direct sampling of the digestate from the same methanization unit. It has the characteristics indicated in Table 8 below:

[0081] [Tables8] Digestate MS % 6.0 MO % 5.7

[0082] In certain tanks, the medium is supplemented with liquid (MHL) or solid (MHP) magnesium hydroxide. The MHP and MHL additives are identical to those described in Example 1.

[0083] Several tanks are used in parallel and arranged as follows: - One tank is left empty, in order to create a blank. - Three tanks, hereafter referred to as control tanks, contain no additives and are loaded as follows: 600.0 g of digestate and 83.4 g of ration. - Three tanks are treated with solid magnesium hydroxide (MHP) and are loaded as follows: 600.0 g of digestate, 83.4 g of ration and 125 mg (on a dry basis) of MHP additive. - Three tanks are treated with liquid magnesium hydroxide (MHL) and are loaded as follows: 600.0 g of digestate, 83.4 g of ration and 180 mg (on a dry basis) of MHL additive.

[0084] The test is conducted over a period of 19 days. This period is not sufficient for the cumulative quantity of biogas to remain constant, and is therefore not a measure of the total Methane Potential but of the CH4 production at 19 days.

[0085] The results are summarized in the following Table 9

[0086] [Tables9] Examples Additive (mg - dry base) content in mg / g DM CH4 production at 19 days (Nm3 / t DM) Control CH4 production at 19 days (Nm3 / t DM) Additive Gain from Additivation Ex MHL C 180 mg MHL 5.5 164,459 +180% Ex MHP C 125 mg MHP 3.8 164,457 +179%

[0087] This example confirms that adding 3.5 to 10 mg of magnesium hydroxide per mg of input organic matter to an input composed of industrial and agricultural waste with 5.70% organic matter increases biomethane production. Furthermore, additive treatment with magnesium hydroxide powder proves to be as effective as additive treatment with a magnesium hydroxide suspension.

[0088] Example 3: Effect of Mg(OH)2 on the kinetics of biomethane production

[0089] This test seeks to evaluate the effect of the addition of magnesium hydroxide on the kinetics of biomethane production.

[0090] The material used is the same as in examples 1 and 2.

[0091] The ratio used is the same as in example 2.

[0092] The additive used (MHP) is the same as that of Example 1.

[0093] Several tanks are used in parallel and arranged as follows: - A vat is left empty, in order to create a white. - Three tanks, hereafter referred to as control tanks, contain no additives and are loaded as follows: 600.0 g of digestate and 83.4 g of ration. - Three tanks are treated with magnesium hydroxide in powder form (MHP) according to the invention and are loaded as follows: 600.0 g of digestate, 83.4 g of ration and 125 mg (on a dry basis) of MHP additive. - Three tanks are treated with magnesium hydroxide in liquid form (MHL) according to the invention and are loaded as follows: 600.0 g of digestate, 83.4 g of ration and 180 mg (on a dry basis) of MHL additive.

[0094] The quantity of methane produced as a function of time is measured. The results are presented in [Fig. 1].

[0095] These results show that magnesium hydroxide in powder form according to the invention has an accelerating effect on the decomposition kinetics of the feed ration. The biogas gain for the additive-treated treatments compared to the control is indeed maximal after only a few days, before gradually decreasing. The additive-treated tanks reach their methanogenic potential more quickly.

Claims

Demands

1. Use of magnesium hydroxide to accelerate the kinetics of biogas production in an anaerobic digester for a given incoming organic matter.

2. Use according to claim 1, characterized in that the dry matter content of magnesium hydroxide, in mg / g of incoming organic matter, is between 3 and 30.

3. Use according to any one of claims 1 or 2, characterized in that the specific surface area of ​​the magnesium hydroxide particles measured by the multipoint BET method by N2 adsorption is between 1 and 100 m2 / g, advantageously between 1 and 50 m2 / g, more advantageously between 5 and 20 m2 / g.

4. Use according to any one of claims 1 to 3, characterized in that the magnesium hydroxide is in the form of an aqueous suspension.

5. Use according to claim 4, characterized in that the aqueous suspension of magnesium hydroxide is obtained by precipitation of magnesium hydroxide in water.

6. Use according to any one of claims 1 to 3, characterized in that the magnesium hydroxide is in powder form.

7. Use according to any one of claims 1 to 6, to further improve the conversion of organic carbon from the incoming organic matter into biomethane in the anaerobic digester.

8. Use according to any one of claims 1 to 7, characterized in that the input organic matter is selected from the organic matter of industrial waste, agricultural waste, energy crops, urban waste and mixtures thereof, in particular from the organic matter of livestock effluents, plant inputs, residues from the food industry, sewage sludge and mixtures thereof, advantageously from the organic matter of slurry, silage, co-products of vegetable processing, co-products of camel processing, sewage sludge and mixtures thereof.

9. Use according to any one of claims 1 to 8, characterized in that the anaerobic digester is part of a dry or wet biogas plant equipped with a continuous stirred tank reactor, a plug flow reactor, a fluidized bed or

10. of a granular sludge bed. Use according to any one of claims 1 to 9, characterized in that the anaerobic digester is intended for the quantitative production of biogas and / or the reduction of carbon pollution within an agricultural input, a municipal or industrial effluent or a waste source.

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