A novel approach for biogas production

Abstract

1. A method for increasing the amount of methane produced from a biodigester, the method comprising: - providing a digester adapted to receive a feed and to capture a biogas composition resulting from biological digestion; - adding to the digester at least one organic material and at least one inoculant capable of converting a portion of the at least one organic material to methane under anaerobic conditions; - providing substantially lignin-free biomass in an amount in the range of 0.1 to 5% w / w of a total feed, including at least one other organic material; - adding the biomass to the digester; - allowing a sufficient time in the digester to decompose at least a portion of the biomass and at least a portion of the organic material to produce a biogas composition comprising methane; - optionally continuously adding the substantially lignin-free biomass in an amount in the range of 0.1 to 5% w / w of a total feed, including at least one other organic material; - capturing the biogas composition; and - optionally storing the biogas.

Description

[Technical Field]

[0001] The present invention relates to the use of cellulose in the production of biogas, and more particularly to the use of low lignin content cellulose as an additive to organic matter in a biodigester. [Background technology]

[0002] Biogas is the product of microbial decomposition of various organic materials (both plant-based and animal-based products) in the absence of oxygen, i.e., in an anaerobic environment. This microbial decomposition in an oxygen-free environment is called anaerobic digestion. Biogas can refer to natural and industrially produced gases and generally contains 45 to 75 percent methane (CH4 or renewable natural gas (RNG)), 25 to 45 percent carbon dioxide (CO2), and trace amounts of various other gases.

[0003] Natural sources of biogas include environments such as swamps, which produce methane through the action of methanogens. A more common source of biogas is associated with industrial activities related to waste disposal, primarily landfills. A second, less widespread, human-derived source of biogas comes from anaerobic digesters, which produce methane and are used to recycle organic waste for use in fertilizing fields. Biogas is produced when organic waste is exposed to microorganisms—bacteria, archaea, and fungi—under anaerobic conditions (the absence of oxygen) to break down organic compounds. This biodegradation yields gas (biogas), liquids, and solids. The latter two, called digestate, can be used as soil amendments in agricultural fields. The composition and nutrient content of the digestate are greatly influenced by the feedstock undergoing biodigestion.

[0004] One end use of industrially produced biogas is to burn it to provide a heat source and generate electricity for buildings, boilers, and possibly even biodigesters. Biogas from landfills and digesters can also be purified to separate the methane (natural gas) from other undesirable components of biogas, such as, but not limited to, carbon dioxide, water vapor, and hydrogen sulfide. This purification process results in renewable natural gas (RNG), which can be used as is, injected into an existing natural gas grid, or even used in natural gas-powered vehicles.

[0005] A major benefit of biogas recovered from biodigesters or landfills is the reduction in fossil fuel use. Using biogas produced from biodigesters or landfills can provide a clean source of electricity, which also reduces the amount of methane released into the atmosphere. Because natural gas (methane) is a greenhouse gas that, weight for weight, is more than 20 times more dangerous to the atmosphere than carbon dioxide over a 20-year period, reducing its release into the atmosphere is desirable. Controlling the release of this gas from its primary industrial sources makes it possible to utilize the energy it provides while providing an environmentally friendly and sustainable alternative to power generation. Anaerobic digestion offers additional benefits to the community and the environment, such as reducing the risk of odor, pathogens, and water pollution associated with livestock manure, and improving soil health.

[0006] The United States currently has over 2,000 biogas systems deployed nationwide, with the potential to add at least 10,000 additional plants, thus creating a significant positive impact on the environment. In fact, properly harnessing the biogas potential in the United States alone would be equivalent to eliminating the emissions of several million cars each year.

[0007] In addition to the environmental benefits, the increased implementation of anaerobic digesters using various agricultural and food wastes will inevitably reduce the costs associated with waste management when such waste would simply be directed to landfills. Further benefits of larger-scale implementation of biodigesters in the United States include the creation of thousands of biogas systems that will support hundreds of thousands of construction jobs, and the resulting biodigester plants will employ tens of thousands of people to operate them.

[0008] Wastewater treatment plants may have on-site anaerobic digesters to process sewage sludge collected during treatment. Solids are separated while water is released, and often the methane produced is simply burned into the atmosphere (i.e., flared) without benefiting from the energy this combustion produces. Only about two-thirds of U.S. wastewater treatment plants with anaerobic digesters actually use the biogas they produce.

[0009] Biogas Feedstock Food waste in landfills accounts for over 20% of the volume of waste present in U.S. landfills. As this food waste decomposes, it is a significant source of natural gas. While landfills can capture the resulting biogas, placing organic waste in landfills does not allow operators to recover nutrients generated from source organic material, such as fats, oils, and grease collected from the food service industry, which are added to anaerobic digesters to increase biogas production.

[0010] Livestock waste is another significant source of methane. An average dairy cow weighing 1,000 pounds produces approximately 80 pounds of manure per day, a non-negligible source of methane. In 2015, it was estimated that livestock waste contributed to 10% of total methane emissions in the United States, yet only 3% of all manure was actually recycled in biodigester plants. This is not only environmentally careless, but also a significant missed opportunity.

[0011] Organic waste in landfills produces biogas, which is released into the atmosphere. Methane produced from landfills ranks as the third largest source (by volume) of such gases associated with human activity in the United States. Microorganisms present in landfills are similar to those found in biodigesters in that they can break down organic material and produce biogas. Because methane is a potent greenhouse gas, it is desirable to capture these emissions and utilize them as a potential energy source.

[0012] Crop residues are a source of organic material that can be processed in anaerobic digesters. These residues are meant to include, but are not limited to, stalks, straw, and plant trimmings. There is enough crop residue to leave some in the field to reduce the amount of soil erosion and harvest the rest for biogas production. It is estimated that there are over 100 million tons of crop residues that can be used in biogas systems. One drawback of crop residues is that they contain lignin, which is very poorly digested in biodigesters. Crop residues are typically mixed with various other organic materials to produce biogas.

[0013] Biogas composition The composition of biogas depends on the feedstock and biodigester conditions, such as temperature, pH, and organic loading. Typical biogas compositions consist of 45–75% methane, 25–45% carbon dioxide, and 5% various other gases. When using methane as an energy source, increasing the methane concentration is desirable. Various treatments can increase methane concentration up to 80%. However, all treatments incur additional costs. The produced biogas contains water vapor, which must be removed before further application. Other gases, including carbon dioxide and hydrogen sulfide, should be removed as much as possible before the biogas can be used as renewable natural gas.

[0014] Lignocellulosic biomass is a widely available resource that can be used for biogas production. Lignin, present in untreated biomass or in pulp after incomplete delignification, is used as part of the feedstock for biodigesters, resulting in reduced microbial activity. This is because lignin is highly resistant to biodegradation, especially under anaerobic conditions. An inverse relationship has been observed between the amount of lignin in plant biomass and its corresponding biomethane potential; lignin, being tightly bound to each other, limits the bioavailability of more readily degradable cellulose. Lignin accumulates as microbial communities preferentially target more readily biodegradable compounds, ultimately limiting microbial activity. Thus, to maximize methane yield, it is preferable to minimize the amount of lignin remaining in the feedstock when using it for anaerobic digestion to produce biogas.

[0015] In light of the above, it is clear that biogas production needs to increase in the future to reduce the country's dependence on petroleum and fossil fuel-based products, especially considering the ease with which such biogas facilities can be implemented. However, to optimize biogas production from such biogas facilities, it would be desirable to be able to provide a more consistent methane-rich biogas output. The composition of biogas produced in such facilities can vary throughout the year depending on the available feedstock used. In many regions, farmers who have biogas facilities on or near their farms can provide some of the feedstock. However, some feedstocks are not necessarily available year-round, and therefore, varying the feedstock composition throughout the year directly affects biogas production and its composition.

[0016] Therefore, there is a need to provide a method for producing methane-rich biogas that can account for variations in feedstock and that can use non-animal feedstocks to supplement other feedstocks used in biogas production. Summary of the Invention

[0017] According to the present invention, it is possible to increase methane yield from a biodigester by carefully adjusting the biomass composition. Preferably, one adjustment that can be made is to incorporate a cellulose-rich additive that is substantially free of lignin. Preferably, the lignin-free cellulose source can be produced by delignifying lignocellulosic biomass with modified Caro's acid. Preferably, the modified Caro's acid used is as disclosed in Canadian Patent Nos. 3,110,553, 3,110,555, and 3,110,558.

[0018] According to a first aspect of the present invention, there is provided a method of increasing methane production from a biodigester, said method comprising the addition of a biomass additive that is substantially free of lignin.

[0019] According to a preferred embodiment of the present invention, the biomass additive is cellulose that has been processed to be substantially free of lignin.

[0020] According to another aspect of the present invention, there is provided a method for increasing and stabilizing the volume of methane produced from a biogas digester by using substantially lignin-free cellulose as an additive to organic waste used in biogas production. Preferably, the substantially lignin-free cellulose is cellulose having less than 10% lignin remaining before the lignocellulosic biomass is delignified. More preferably, the substantially lignin-free cellulose is cellulose having less than 5% lignin remaining before the lignocellulosic biomass is delignified. Even more preferably, the substantially lignin-free cellulose is cellulose having less than 2.5% lignin remaining before the lignocellulosic biomass is delignified. Even more preferably, the substantially lignin-free cellulose is cellulose having less than 1% lignin remaining before the lignocellulosic biomass is delignified.

[0021] According to a preferred embodiment of the present invention, the substantially lignin-free cellulose is present in an amount ranging from up to 5% w / w of the total organic feed to the biodigester. Preferably, the substantially lignin-free cellulose is present in an amount ranging from 0.1 to 2.5% w / w of the total organic feed to the biodigester. More preferably, the substantially lignin-free cellulose is present in an amount ranging from 0.1 to 1% w / w of the total organic feed to the biodigester.

[0022] According to another aspect of the present invention, there is provided a method for producing biogas, comprising the steps of: - providing a digester adapted to receive the feed and capture a biogas composition resulting from anaerobic biological digestion; - adding to the digester at least one organic material and at least one inoculum capable of converting a portion of the at least one organic material into methane under anaerobic conditions; - providing a substantially lignin-free biomass in an amount ranging from 0.1 to 5% w / w of the total feed; - adding said biomass to said digester along with at least one other organic material; - allowing a sufficient time in the digester to decompose at least a portion of the biomass and at least a portion of the organic material to produce a biogas composition comprising methane; capturing said biogas composition; - optionally storing the biogas; A method is provided, comprising:

[0023] According to another aspect of the present invention, there is provided a method for increasing the amount of methane produced from a biodigester, said method comprising: - providing a digester adapted to receive a feed and to feed and capture a biogas composition resulting from anaerobic biological digestion; - adding to the digester at least one organic material and at least one inoculum capable of converting a portion of the at least one organic material into methane under anaerobic conditions; - providing a substantially lignin-free biomass in an amount ranging from 0.1 to 5% w / w of the total feed; - adding said biomass to said digester along with at least one other organic material; - allowing a sufficient time in the digester to decompose at least a portion of the biomass and at least a portion of the organic material to produce a biogas composition comprising methane; capturing said biogas composition; - optionally storing the biogas; A method is provided, comprising:

[0024] According to another aspect of the present invention, there is provided the use of substantially lignin-free cellulose as an additive to organic waste for biogas production to increase the volume of methane produced from the biogas digester, wherein the cellulose is added in an amount not exceeding 5% of the total feed in the biogas digester. Preferably, the substantially lignin-free cellulose stabilizes the volume of methane produced from the biogas digester.

[0025] According to another aspect of the present invention, there is provided the use of substantially lignin-free cellulose as an additive to organic waste intended for biogas production to reduce the volume of carbon dioxide produced from a biogas digester.

[0026] According to a preferred embodiment of the invention, the substantially lignin-free cellulose has a particle size in the range of up to 800 microns and a kappa number of less than 10. Preferably, the substantially lignin-free cellulose has a particle size in the range of 30-50 microns and a kappa number of less than 5. Preferably, the substantially lignin-free cellulose has a particle size in the range of 30-50 microns and a kappa number of less than 2. According to a preferred embodiment of the invention, the substantially lignin-free cellulose has a particle size in the range of 30-50 μm in length and about 4 μm in width and a kappa number of less than 2.

[0027] According to another aspect of the present invention, there is provided a method for producing biogas, said method comprising: - providing a digester adapted to receive the feed and capture a biogas composition resulting from anaerobic biological digestion; -the below described: at least one organic material, at least one inoculum capable of converting a portion of said at least one organic material into methane under anaerobic conditions; Biomass substantially free of lignin in an amount ranging between 0.1 and 5% w / w of the total feed; providing a supply comprising: - adding said feed to said digester; - allowing a sufficient time for the feed to decompose and decompose at least a portion of the biomass and at least a portion of the organic material to produce a biogas composition comprising methane; - optionally continuously adding said biomass substantially free of lignin in an amount ranging from 0.1 to 5% w / w of the total feed containing at least one other organic material; capturing said biogas composition; - optionally storing at least a portion of said biogas; A method is provided that includes:

[0028] Those skilled in the art will appreciate that biogas is produced after organic material (plant and animal products) is decomposed when exposed to microorganisms in an oxygen-free environment (i.e., under anaerobic conditions). This is also referred to as anaerobic digestion. Anaerobic digestion of organic material produces biogas and residual solids and liquids, called digestate. The digestate is rich in nutrients that were present in the original organic material, but are now readily available to plants and soil. The composition and nutrient content of the digestate is determined by the type of feedstock used to decompose the organic matter added to the digester.

[0029] According to a preferred embodiment of the present invention, a method for producing biogas is provided that uses a substantially lignin-free cellulose additive obtained from exposing lignocellulosic feedstock to modified Caro's acid under conditions substantially milder than other conventionally used pulping processes (such as kraft pulping). This approach allows for an overall more environmentally friendly process because the lignocellulosic feedstock does not divert food resources from animals or humans and uses a very low energy input delignification process. According to a preferred embodiment of the present invention, the biomass additive is cellulose, wherein the cellulose has a hemicellulose content of less than 15%, preferably less than 10%, more preferably less than 5%, and a kappa number of less than 10, more preferably less than 5, and even more preferably less than 2.

[0030] Biogas contains several gases, including but not limited to methane, carbon dioxide, hydrogen sulfide, and volatile fatty acids. In most cases, the remaining solids and liquids ("digestate") can be used as fertilizer for soil.

[0031] Features and advantages of the embodiments of the present application will become apparent from the following detailed description and accompanying drawings. [Brief explanation of the drawings]

[0032] [Figure 1] 1 is a graphical depiction of biogas production for samples from Experiment #1. [Figure 2] 1 is a graphical depiction of the methane percentage of samples from Experiment #1. [Figure 3] 1 is a graphical depiction of cumulative methane in mL / g VS of substantially lignin-free cellulose compared to a typical lignocellulosic digester feed (straw) from Experiment #2. [Figure 4] 1 is a graphical depiction of methane production for samples from Experiment #3. [Figure 5] 1 is a graphical depiction of biogas production and substantially lignin-free cellulose addition over time in a field trial. [Figure 6] 1 is a graphical depiction of biogas production and substantially lignin-free cellulose accumulation and theoretical biodegradation over time in a field trial. [Figure 7] 1 is a graphical depiction of FOS / TAC ratio and substantially lignin-free cellulose addition over time in a field trial. DETAILED DESCRIPTION OF THE INVENTION

[0033] According to a preferred embodiment of the present invention, a method for increasing methane production from a biogas digester is provided.

[0034] It has surprisingly been discovered that the use of substantially lignin-free cellulose as a small amount of additive to an organic waste mass for biogas production when placed in a biodigester with suitable microorganisms can increase the volume of methane gas produced. It should be noted that preferably, the amount of substantially lignin-free cellulose added to the biodigester produced a disproportionate amount of methane based on the mass input in the system.

[0035] According to a preferred embodiment of the present invention, there is provided a method for increasing and stabilizing the volume of methane produced from a biogas digester by using substantially lignin-free cellulose as a partial additive to organic waste intended for biogas production. Surprisingly, it has been found that the use of substantially lignin-free cellulose as a minor additive to an organic waste mass intended for biogas production when placed in a biodigester with suitable microorganisms can increase the volume of methane gas produced.

[0036] According to a preferred embodiment of the present invention, the composition of the gas comprises at least 60% methane, which is used as an efficient energy source.

[0037] Currently, biomass fed to anaerobic digesters is not delignified, and the presence of lignin causes inhibition of biodegradation of said biomass by the microorganisms present in the biodigester, thereby preventing optimal methane production from such units. Preferably, by using cellulose obtained from delignification of lignocellulosic biomass using modified Caro's acid as an additive to the anaerobic digester, the cellulose is in a form that is more readily available to the microorganisms in the biodigester.

[0038] According to a preferred embodiment of the present invention, the biomass additive is cellulose that has been processed to be substantially free of lignin.

[0039] Preferably, the addition of a substantially lignin-free biomass additive allows for increased methane production in the biodigester when the biomass additive is a small fraction of the total biodigester content. Preferably, the biomass additive is cellulose and is present in an amount ranging up to 5% w / w of the total organic feed in the biodigester. Preferably, the cellulose is hydrated, and in some instances, the water may be up to 90% by weight of the cellulose. According to a preferred embodiment, the cellulose is present in an amount ranging from 0.1 to 5.0% w / w of the total organic feed in the biodigester. According to a preferred embodiment, the substantially lignin-free cellulose is present in an amount ranging from 0.1 to 2.5% w / w of the total organic feed to the biodigester. According to yet another preferred embodiment, the cellulose is present in an amount of about 1% w / w of the total organic feed in the biodigester. Preferably, the amount of biomass additive may be adjusted based on the composition of the organic content present in the digester. Also, considering the potential for variation between different biodigesters (due to their different organic content and microbial populations), it is desirable to perform a preliminary determination to evaluate the optimal concentration of biomass additive to avoid incorporating suboptimal amounts, as the additive may be more expensive than other organic contents within the biodigester.

[0040] It is generally accepted that biogas is primarily formed by the decomposition of organic materials such as carbohydrates, proteins, and lipids. The lignin fraction present in various feedstocks added to digesters is known to be difficult to decompose by the microorganisms present in digesters. Anaerobic digestion of lignin has been observed in certain environments, but it requires a variety of microorganisms whose primary pathway involves enzymatic depolymerization of lignin. Even when these organisms are present, the process tends to be slow. The complexity of the microbial communities present in these systems makes them very difficult to reproduce on an industrial scale, making the applicability of anaerobic digestion of lignin a complex and challenging topic.

[0041] In kraft pulping, approximately 90% of the lignin present in the processed biomass is dissolved and removed from it. The remaining 10% of the original lignin remains attached to the cellulose fibers and is responsible for the brown color of unbleached pulp. When kraft pulp is added to a biodigester, the results are suboptimal because lignin is known to be resistant to degradation.

[0042] The addition of cellulose-rich additives that are essentially lignin-free has made it possible to increase methane production in biodigesters. Delignification of biomass by traditional methods, such as kraft pulping, produces pulp that is still high in lignin. Removal of the remaining lignin is typically achieved through a bleaching process, which involves harsh chemicals and conditions that are energy and environmentally unfriendly. Using bleached pulp in biodigesters is simply not commercially viable or applicable on an industrial scale due to the prohibitive costs.

[0043] According to a preferred embodiment of the present invention, the biomass additive is unbleached cellulose. Preferably, the cellulose is obtained by delignification of a biomass feedstock by exposure to modified Caro's acid according to the following method: - providing a container; - providing a biomass comprising lignin, hemicellulose and cellulose fibers in said vessel; providing a sulfuric acid component; - providing a peroxide component; - exposing said biomass to said sulfate and peroxide components; - contacting the sulfuric acid and peroxide components with the biomass for a period of time sufficient to cause a delignification reaction to occur and remove greater than 90% by weight of the lignin and hemicellulose from the biomass; Includes:

[0044] Preferably, a biomass containing lignin, hemicellulose, and cellulose fiber is exposed to a modified Caro's acid composition selected from the group consisting of Composition A; Composition B, and Composition C; The composition A is sulfuric acid in an amount ranging from 20 to 70% by weight of the total weight of the composition; - a modified compound containing an amine moiety and a sulfonic acid moiety selected from the group consisting of taurine; taurine derivatives; and taurine-related compounds; -Peroxide Including, The composition B is - alkyl sulfonic acids; and -Peroxide wherein the acid is present in an amount ranging from 40 to 80% by weight of the total weight of the composition, and the peroxide is present in an amount ranging from 10 to 40% by weight of the total weight of the composition; The composition C is -sulfuric acid; - Two-component modifiers containing: compounds containing an amine moiety; and -compounds containing a sulfonic acid moiety; and -Containing peroxides, Includes:

[0045] According to a preferred embodiment of the present invention, exposing the biomass to the modified Caro's acid composition causes a delignification reaction, allowing for the removal of more than 90% by weight of the lignin and hemicellulose from the biomass. Preferably, the substantially lignin-free cellulose is obtained from a delignification process of lignocellulosic material in the presence of the aforementioned modified Caro's acid and has not undergone a drying step before being added to the digester. Because the cellulose is not dried once obtained, it is more bioavailable than dried cellulose. This may be due to the absence or at least reduction of keratinization in the cellulose obtained after the delignification process. Cellulose keratinization is a loss that occurs as a result of swelling of the cellulose fiber walls upon drying of the cellulose. Drying the cellulose results in strengthening of the cellulosic fibers, which reduces their ability to form interfiber bonds.

[0046] Preferably, the delignification reaction is carried out at a temperature below 55°C by a method selected from the group consisting of: - adding water to said container; adding biomass to said vessel; and -Use a heat exchanger.

[0047] Preferably, the sulfuric acid, the compound containing an amine moiety and a sulfonic acid moiety, and the peroxide are present in a molar ratio of 1:1:1 or greater, and preferably, the sulfuric acid, the compound containing an amine moiety and a sulfonic acid moiety, and the peroxide are present in a molar ratio of 15:1:1 or less.

[0048] According to a preferred embodiment of the present invention, the sulfuric acid and the compound comprising an amine moiety and a sulfonic acid moiety are present in a molar ratio of 3:1 or greater.

[0049] According to a preferred embodiment of the present invention, the compound comprising an amine moiety and a sulfonic acid moiety is selected from the group consisting of taurine; taurine derivatives; and taurine-related compounds.

[0050] According to a preferred embodiment of the present invention, the taurine derivative or taurine-related compound is selected from the group consisting of taurolidine, taurocholic acid, taurocelecholic acid, tauromustine, 5-taurinomethyluridine and 5-taurinomethyl-2-thiouridine, homotaurine (tramiprosate), acamprosate, and taurates, and aminoalkylsulfonic acids, where alkyl is selected from the group consisting of C1-C5 linear alkyls and C1-C5 branched alkyls. Preferably, the linear alkylaminosulfonic acids are selected from the group consisting of methyl, ethyl (taurine), propyl, and butyl. Preferably, the branched aminoalkyl sulfonic acid is selected from the group consisting of isopropyl; isobutyl; and isopentyl.

[0051] According to a preferred embodiment of the present invention, the compound comprising an amine moiety and a sulfonic acid moiety is taurine.

[0052] According to a preferred embodiment of the invention, the sulfuric acid and the compound comprising an amine moiety and a sulfonic acid moiety are present in a molar ratio of 3:1 or greater.

[0053] According to a preferred embodiment of the present invention, the compound comprising an amine moiety is an alkanolamine selected from the group consisting of monoethanolamine; diethanolamine; triethanolamine; and combinations thereof.

[0054] According to a preferred embodiment of the present invention, said compound comprising a sulfonic acid moiety is selected from the group consisting of alkylsulfonic acids and combinations thereof.

[0055] According to a preferred embodiment of the present invention, the alkyl sulfonic acid is selected from the group consisting of alkyl sulfonic acids in which the alkyl group ranges from C1 to C6, and which are linear or branched, and combinations thereof.

[0056] According to a preferred embodiment of the present invention, the alkyl sulfonic acid is selected from the group consisting of methanesulfonic acid; ethanesulfonic acid; propanesulfonic acid; 2-propanesulfonic acid; isobutylsulfonic acid; t-butylsulfonic acid; butanesulfonic acid; isopentylsulfonic acid; t-pentylsulfonic acid; pentanesulfonic acid; t-butylhexanesulfonic acid; and combinations thereof.

[0057] According to a preferred embodiment of the present invention, the alkyl sulfonic acid and the peroxide are present in a molar ratio of 1:1 or greater.

[0058] According to a preferred embodiment of the present invention, said compound comprising a sulfonic acid moiety is methanesulfonic acid.

[0059] According to a preferred embodiment of the present invention, in composition C, the sulfuric acid and the compound comprising an amine moiety and the compound comprising a sulfonic acid moiety are present in a molar ratio of 1:1:1 or greater.

[0060] According to a preferred embodiment of the present invention, in composition C, the sulfuric acid, the compound comprising an amine moiety and the compound comprising a sulfonic acid moiety are present in a molar ratio ranging from 28:1:1 to 2:1:1.

[0061] According to a preferred embodiment of the present invention, the biomass additive is cellulose having a hemicellulose content of less than 15%, preferably less than 10%, more preferably less than 5%, and a kappa number of less than 10, more preferably less than 5, even more preferably less than 2.

[0062] Laboratory-scale testing Anaerobic digestion experiments were conducted using serum bottles. Serum bottles were set up by adding feedstock consisting of manure, inoculant (digestate from a commercial-scale digester), and agricultural waste and / or cellulose obtained through a delignification process involving the use of modified Caro's acid, as previously described. Each serum bottle batch was set up to run under mesophilic conditions. Biogas production and methane concentrations were measured periodically throughout the experiment. FOS / TAC measurements (measurements of volatile fatty acids and total organic carbon; an industry standard for assessing digester balance) were performed throughout the experiment.

[0063] According to a preferred embodiment of the present invention, the cellulose is a low kappa cellulose, said low kappa cellulose having the following characteristics: a particle size in the range of up to 800 microns and a kappa number of less than 10, more preferably less than 5, even more preferably less than 2.

[0064] Experiment #1 - Determining the Effect of a Substantially Lignin-Free Cellulose Additive For the first batch, a basic proof-of-concept was tested to see if the presence of low-lignin content cellulose would increase methane production in the system. Also, the performance of replacing a portion of the manure with cellulose (45% manure instead of 50% manure) or replacing a portion of the agricultural waste feedstock with cellulose (15% feedstock instead of 20%) could be evaluated and be more efficient.

[0065] The cellulose used in the experiment has an aspect ratio of approximately 7.5. The aspect ratio of a particle, in this case a cellulose fiber, is determined by the ratio of its length to its width. In the above case, the particle is approximately 30-50 μm long and approximately 4 μm wide.

[0066] This was tested by preparing the following samples (n=4): 1. Inoculum only (n=1) 2. 0% cellulose, cow manure 3. 5% cellulose, replacing manure 4. 5% cellulose, replacing the feedstock

[0067] Each sample contained 50% manure except for sample 4 (45% manure), and all samples contained 20% inoculant. The feedstock used was a combination of potatoes, flotation screening, and various other agricultural wastes. Samples were incubated at 40°C.

[0068] Throughout the experiment, it was observed that the cellulose-containing samples produced more biogas than the non-cellulose-containing samples (Figure 1). Methane concentrations were immediately highest in the cellulose-partially replaced feed samples, and this trend continued throughout the month. Methane concentrations in samples where cellulose replaced part of the feed were consistently higher than all other samples. By day 10, methane concentrations spiked into the cellulose-partially replaced manure samples, but did not continue to increase as much as the cellulose-substituted feed samples did (Figure 2).

[0069] Experiment #2 - Determination of Chemical Oxygen Demand (COD) and Biomethane Potential (BMP) COD is a measure of the amount of oxygen that can be consumed by reactions in the digester. It is used to calculate BMP, a substrate characteristic that defines the maximum amount of methane that can be produced by anaerobic digestion. It is typically measured in mL of methane per gram of volatile solids of the substrate. This value is commonly discussed in the biogas community when discussing potential feed values. BMP is typically tested in the laboratory in serum bottles or via automated BMP testing equipment.

[0070] Experiments were conducted to obtain the biomethane potential (BMP) of substantially lignin-free cellulose and compare it to the BMP of a typical lignocellulosic digester feed (straw).

[0071] The substrate (cellulose or straw) is digested in a bottle containing the digestate (inoculum) along with a blank bottle containing only the digestate. The methane value obtained from the blank is subtracted from the methane value obtained from the substrate-containing bottle to obtain the final cumulative methane production from the substrate alone.

[0072] The substrates were tested at a substrate-to-digestate ratio of 0.1:1. The chemical oxygen demand (COD), theoretical BMP, and volatile solids (VS) of each substrate were measured. Biogas production in the bottles was measured over a 78-day period. The results are shown in Table 1. [Table 1] Table 1 shows that cellulose has a significantly higher theoretical biomethane potential (BMP) than straw, a common agricultural waste material used in on-farm anaerobic digesters. Experimental BMP testing confirmed these results, with the average cumulative milliliters of methane produced per gram of volatile solids being significantly higher for substantially lignin-free cellulose than for straw (Figure 3). This suggests that the methane production potential per gram of substantially lignin-free cellulose is significantly higher than the methane production potential per gram of straw. To achieve the same amount of methane production, a much larger volume of straw would need to be fed into the digester than cellulose. This suggests that small amounts of substantially lignin-free cellulose can be fed into an anaerobic digester system to significantly increase methane production.

[0073] Experiment #3 - Determination of methane production on a laboratory scale Serum bottles were filled with digestate, manure, and agricultural feed. A substantially lignin-free cellulose additive was added to a portion of the bottle to replace a portion of the agricultural feedstock. Methane concentrations were measured over time using GC-FID. Biogas production was monitored throughout the experiment. The results of the test are shown in Figure 4.

[0074] The bottles contained approximately 7 g of manure and agricultural feed combined, and in the case of cellulose, the agricultural feed was partially replaced with cellulose to achieve the same mass. Cellulose was present in an amount of approximately 3.5% of the total combined feed. Bottles containing essentially 0.5% cellulose supplementation of the total lignin-free system produced nearly four times more methane per gram of volatile solids compared to no supplementation.

[0075] Field Test Two 2,112m 3 A field trial was conducted with an anaerobic digester connected to the system. The digester was capable of processing over 17,000 tons of organic waste per year, including manure, crop silage, and organic waste and refuse. The trial lasted for three weeks (no changes in feed) and the biodigester was monitored for seven weeks.

[0076] Observation of biogas composition during the test A short 7-day delay was observed between the addition of the cellulose peak and changes in biogas composition (Figure 5). Because cellulose is metabolized by microorganisms in the digester, some members of the microbial community are trophic. A symbiotic microbial community contains many different types of microorganisms with different metabolic pathways, and the products of these different metabolic pathways benefit other microorganisms in the community. In this type of interaction, cellulose metabolic products are transferred between two or more metabolically diverse microorganisms. The growth of one microorganism depends on nutrients, growth factors, or substrates provided by the other microorganism. Cellulose is biodegraded into smaller sugars (such as cellobiose or glucose). These sugars are then fermented by acetogenic microorganisms to acid and carbon dioxide, and these products can then be converted to methane by methanogenic archaea. The initial delay observed is likely due to the time it takes for all these processes to occur. After cellulose addition, a sustained increase in methane concentration and a decrease in carbon dioxide (approximately 5–10% relative to baseline) were observed. After the cellulose feed was stopped for the same 7-day delay, a sharp decrease in methane (>10%) and a corresponding increase in carbon dioxide (>20%) was also observed. Biogas production remained constant throughout the test, indicating that an increase in methane % corresponded to an increase in the volume of methane produced. The data collected during this test reveal that the use of cellulose as an additive results in a sustained increase in methane production, as well as a decrease in the carbon dioxide portion of the biogas produced.

[0077] The above results demonstrate the use of substantially lignin-free cellulose as an additive to organic waste for biogas production to increase the volume of methane produced from a biogas digester, where the cellulose is added in an amount not exceeding 5% of the total feed in the biogas digester. The above results also demonstrate the use of substantially lignin-free cellulose as an additive to stabilize the volume of methane produced from a biogas digester. Furthermore, the above results also support the use of substantially lignin-free cellulose as an additive to organic waste for biogas production to reduce the volume of carbon dioxide produced from a biogas digester.

[0078] The biogas changes observed in Figure 6 are consistent with the theoretical cellulose biodegradation calculated from the use of cellulose as an additive and the experimental BMP tests described above (Figure 3).

[0079] FOS / TAC ratio observed during the study The FOS / TAC ratio is an index for evaluating fermentation processes. The FOS / TAC value is the ratio of volatile organic acids (or "Fluchtige Organische Sauren" in German, FOS) to the total alkalinity or buffering capacity of the anaerobic digestion system (or "Total Anorganic Carbon" in German, TAC). Anaerobic digestion has four typical microbial transformations: hydrolysis, acidogenesis, acetogenesis, and methanogenesis. During acidogenesis, compounds obtained from the hydrolysis stage (i.e., sugars, amino acids, etc.) are decomposed by acidogenic microorganisms to produce volatile fatty acids (VFAs), such as acetic acid, propionic acid, and butyric acid. These VFAs are then consumed by acetogenic and methanogenic microorganisms for the production of biogas and, therefore, methane. As VFAs begin to accumulate, the buffering capacity of the digester (the TAC portion of the ratio) becomes a key parameter for countering the VFA-induced low pH and maintaining an optimal pH, which is crucial for the successful and correct functioning of the anaerobic digester.

[0080] An FOS / TAC ratio of 0.3 to 0.4 is optimal for peak biogas production in anaerobic digesters. This ratio is an excellent indicator of digester health, as it provides a guide to the volume of feed required by the digester, the stability of the microbial population, and the potential accumulation of volatile organic acids. The FOS / TAC ratio is affected by changes in feed rate, feed composition, mixing, temperature, pH, and microbial population shifts.

[0081] By providing a consistent carbon source, the addition of a cellulose-rich additive, essentially free of lignin, allowed the optimal FOS / TAC ratio to be achieved, even at low supplementation levels. As supplementation decreased, the FOS / TAC ratio subsequently fell outside the optimal range. Consistent supplementation using an essentially lignin-free cellulose additive potentially allows for a more stable nutrient microbial community. The large number of microorganisms simultaneously working to convert biological waste into biogas can be more consistently maintained when this easily accessible carbon source is provided. Table 2 highlights various ranges of ratios and indications of biodigester health. [Table 2]

[0082] Referring to Figure 7, it can be observed that the FOS / TAC values of the produced biogas were consistently lower than the optimal range before the start of the test. The FOS / TAC ratio is observed to steadily increase to achieve optimal levels (i.e., healthy levels) with the addition of cellulose.

[0083] The addition of a cellulose-rich additive, essentially lignin-free, as a supplement results in an FOS / TAC ratio within the optimal range. Maintaining the FOS / TAC ratio within the optimal range is important, which is not easy when the feedstock added to the bioreactor varies depending on its availability. Referring to Figure 7, it is established that the addition of cellulose supplements to anaerobic digestion enhances the health of the anaerobic digestion, resulting in a better FOS / TAC ratio and increased methane content in the resulting biogas stream.

[0084] According to a preferred embodiment of the present invention, cellulose additives for anaerobic digestion are only required at a minimal loading of the total daily feed (including organic material + cellulose) of the anaerobic digester (<0.3%) for significant sustained benefits.

[0085] Although the foregoing invention has been described in some detail for purposes of clarity and understanding, those skilled in the art, once familiar with the present disclosure, will appreciate that various changes in form and detail can be made therein without departing from the true scope of the invention as set forth in the appended claims.

Claims

1. A method for increasing and stabilizing the volume of methane produced from a biogas digester by using substantially lignin-free cellulose as an additive to the organic waste used in biogas production.

2. 10. The method of claim 1, wherein the substantially lignin-free cellulose is cellulose containing less than 10% lignin.

3. 10. The method of claim 1, wherein the substantially lignin-free cellulose is cellulose containing less than 5% lignin.

4. 10. The method of claim 1, wherein the substantially lignin-free cellulose is cellulose containing less than 2.5% lignin.

5. 10. The method of claim 1, wherein the substantially lignin-free cellulose is cellulose containing less than 1% lignin.

6. 6. The method of any one of claims 1 to 5, wherein the lignin-free cellulose is present in an amount ranging up to 5% w / w of the total organic feed in the biodigester.

7. 6. The method of any one of claims 1 to 5, wherein the lignin-free cellulose is present in an amount in the range of 0.1 to 2.5% w / w of the total organic feed to the biodigester.

8. 6. The method of any one of claims 1 to 5, wherein the lignin-free cellulose is present in an amount in the range of 0.1 to 1% w / w of the total organic feed in the biodigester.

9. 1. A method for producing biogas, said method comprising: providing a digester adapted to receive the feed and capture a biogas composition resulting from the biodigestion; adding to the digester at least one organic material and at least one inoculum capable of converting a portion of the at least one organic material to methane under anaerobic conditions; providing a substantially lignin-free biomass in an amount ranging from 0.1 to 5% w / w of the total feed, including at least one other organic material; adding the biomass to the digester; allowing a sufficient time in the digester to decompose at least a portion of the biomass and at least a portion of the organic material to produce a biogas composition comprising methane; Optionally, continuously adding said substantially lignin-free biomass in an amount ranging from 0.1 to 5% w / w of the total feed including at least one other organic material; capturing the biogas composition; Optionally, storing the biogas; A method comprising:

10. 1. A method for increasing the amount of methane produced from a biodigester, the method comprising: providing a digester adapted to receive the feed and capture a biogas composition resulting from the biodigestion; adding to the digester at least one organic material and at least one inoculum capable of converting a portion of the at least one organic material to methane under anaerobic conditions; providing a substantially lignin-free biomass in an amount ranging from 0.1 to 5% w / w of the total feed, including at least one other organic material; adding the biomass to the digester; allowing a sufficient time in the digester to decompose at least a portion of the biomass and at least a portion of the organic material to produce a biogas composition comprising methane; Optionally, continuously adding said substantially lignin-free biomass in an amount ranging from 0.1 to 5% w / w of the total feed including at least one other organic material; capturing the biogas composition; Optionally, storing the biogas; A method comprising:

11. 1. Use of substantially lignin-free cellulose as an additive to organic waste for the purpose of biogas production, to increase the volume of methane produced from a biogas digester, wherein the cellulose is added in an amount not exceeding 5 wt% of the total feed in the biogas digester.

12. 12. The use of claim 11, wherein the substantially lignin-free cellulose stabilizes the volume of methane produced from a biogas digester.

13. 1. Use of substantially lignin-free cellulose as an additive to organic waste for biogas production to reduce the volume of carbon dioxide produced from a biogas digester.

14. 14. The use according to any one of claims 11 to 13, wherein the substantially lignin-free cellulose has a particle size in the range of up to 800 microns and a kappa number of less than 10.

15. 14. The use according to any one of claims 11 to 13, wherein the substantially lignin-free cellulose has a particle size in the range of 800 microns and a Kappa number of less than 5.

16. 14. The use according to any one of claims 11 to 13, wherein the substantially lignin-free cellulose is obtained from a delignification process of lignocellulosic material in the presence of modified Caro's acid and has not undergone a drying step before being added to the digester.

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