Reduction of retention time in biogas reactors

Abstract

The present invention provides systems and methods for increasing throughput and biogas production in a biogas reactor by pretreatment with hyperthermophilic organisms so that the retention time of biomass in the bioreactors can be decreased.

Description

REDUCTION OF RETENTION TIME IN BIOGAS REACTORS

[0001] The present application claims priority to U.S. Provisional Application No. 63 / 549,079, filed February 2, 2024, which is incorporated herein by reference in its entirety.Field

[0002] The present invention provides systems and methods for increasing throughput and biogas production in a biogas reactor by pretreatment with hyperthermophilic organisms so that the retention time of biomass in the bioreactors can be decreased.Background

[0003] Biogas is produced by the anaerobic digestion of organic materials such as sewage sludge, animal waste, and municipal solid waste (MSW). As a sustainable clean energy carrier, biogas is an important source of energy for heat and electricity generation as it is one of the most promising renewable energy sources in the world. Biogas is produced by the anaerobic digestion (AD) of organic matter, such as manure, MSW, sewage sludge, biodegradable wastes, and agricultural slurry, under anaerobic conditions with the help of microorganisms .

[0004] Commercial biogas production has increased since it can be used as a fuel or source of energy, while also contributing to lower greenhouse gas (GHG) concentrations when collected in a closed process and not released into the atmosphere. The biogas produced contains 50-70% CH4and 30-50% CO2, with minor components such as hydrogen sulfide (H2S), nitrogen (N2), oxygen (O2), siloxanes, volatile organic compounds (VOCs), carbon monoxide (CO), and ammonia (NH3). Biogas usage is expected to double in the next few years, from 14.5 GW in 2012 to 29.5 GW in 2022, according to estimates. The components present in biogas comprise methane (55-75%), carbon dioxide (25-45%), nitrogen (0-5%), hydrogen (0-1%), hydrogen sulfide (0-1%), and oxygen (0-2%). Sewage sludge mainly contains proteins, sugars, detergents, phenols, and lipids.

[0005] During biogas production, biopolymers are converted to biogas under anaerobic conditions. Anaerobic digestion involves hydrolysis, acidogenesis, acetogenesis, and methanogenesis. Hydrolysis involves the breakdown of biopolymers into their monomers in the presence of water. Acidogenesis involves the formation of volatile acids from monomers. Acetogenesis produces acetates and acetic acid from various volatile acids. Finally, acetates and acetic acid are converted to methane and carbon dioxide during methanogenesis.Anaerobic digestion occurs in the presence of co-cultures containing hydrolytic, acidogenic, acetogenic, and methanogenic organisms.

[0006] While there are many conventional systems and methods available for biogas production, what is needed in the art are systems and methods that improve the efficiency of biogas production.Summary of the Invention

[0007] The present invention provides systems and methods for increasing throughput and biogas production in a biogas reactor by pretreatment with hyperthermophilic organisms so that the retention time of biomass in the bioreactors can be decreased.

[0008] Accordingly, in some embodiments, the present invention provides an industrial scale process for producing biogas comprising: in a first bioreactor, fermenting a biomass with a population of at least one genus of a hyperthermophilic organism to provide a pretreated biomass; introducing the pretreated biomass into a second bioreactor having a volume of from 1000 m3to 20000 m3and having therein a microbial consortium comprising methanogenic organisms; fermenting the pretreated biomass in the second bioreactor to produce biogas under conditions such that 1) the hydraulic retention time of the pretreated biomass in the second bioreactor averages from 8 to 25 days; and / or 2) biogas is produced at the same and / or increased levels as compared to biogas production without hyperthermophilic pretreatment when the hydraulic retention time of the pretreated biomass in the second bioreactor averages from 8 to 25 days; and / or 3) biogas is produced at the same and / or increased levels as compared to biogas production without hyperthermophilic pretreatment when the hydraulic retention time of the pretreated biomass in the second bioreactor is reduced by from 20% to 80% as compared to the average retention time in a commercial biogas reactor.

[0009] In some preferred embodiments, the hydraulic retention time of the pretreated biomass in the second bioreactor averages from 10 to 25 days, 15 to 25 days, 20 to 25 days, 10 to 22 days, 15 to 22 days, 10 to 20 days, 15 to 20 days, 8 to 22 days, 8 to 20 days or 8 to 15 days. In some preferred embodiments, the hydraulic retention time of the pretreated biomass in the second bioreactor is reduced by from 20% to 70%, from 20% to 60%, from 20% to 50%, or from 20% to 40% as compared to the average retention time in a commercial biogas reactor.

[0010] In some preferred embodiments, the hydraulic retention time of the biomass in the first bioreactor averages from 4 to 24 hours, 5 to 16 hours, or 6 to 12 hours.

[0011] In some preferred embodiments, the volume of the second bioreactor is from 5000 m3to 20000 m3, 5000 m3to 15000 m3, 5000 m3to 12000 m3, 7000 m3to 20000 m3, 7000 m3to 15000 m3, 7000 m3to 12000 m3, 8000 m3to 20000 m3, 8000 m3to 15000 m3, or 8000 m3to 12000 m3.

[0012] In some preferred embodiments, the volume of the first bioreactor is from 10 m3to 10000 m3, and most preferably from 1000 m3to 10000 m3.

[0013] In some preferred embodiments, the biomass is selected from the group consisting of sewage, agricultural waste products, brewery grain by-products, food waste, forestry waste, crops, grass, seaweed, plankton, algae, fish, fish waste, corn, potato waste, sugar cane waste, sugar beet waste, straw, paper waste, chicken manure, fish manure, fish sludge, cow manure, hog manure, switchgrass and combinations thereof.

[0014] In some preferred embodiments, the at least one genus of a hyperthermophilic organism is selected from the group consisting of the genera Pyrococcus, Thermococcus, Acidianus, Palaeococcus, Thermoplasma, Pyrobaculum, Pyrolobus, Pyrodictium, Methanotehrmus, Methanopyrus, Fervidobacterium, Thermotoga, and combinations thereof. In some particularly preferred embodiments, the at least one genus of a hyperthermophilic organism is Thermotoga.

[0015] In some preferred embodiments, the step of fermenting a biomass with a population of at least one genus of a hyperthermophilic organism to provide a pretreated biomass is performed at a temperature range of from 70.0 to 105.0°C, 70.0 to 100.0°C, 70.0 to 90.0°C, 70.0 to 85.0°C, 75.0 to 100.0°C, 75.0 to 90.0°C, 75.0 to 85.0°C, 76.0 to 84.0°C, 77.0 to 83.0°C, 78.0 to 82.0°C, 75.0 to 79.0°C, or 76.0 to 79.0°C.

[0016] In some preferred embodiments, the step of fermenting a biomass with a population of at least one genus of a hyperthermophilic organism to provide a pretreated biomass comprises fermentation in the presence of a cell density of at least one genus of a hyperthermophilic organism of greater 106, 107, 108or most preferably 109cells / ml, or from 106to 1010, 107to 1010, 108to 1010or 107to 1010or 108to 1010cells / ml.

[0017] In some preferred embodiments, the methods further comprise removing the biogas from the second bioreactor.Brief Description Of The Drawings

[0018] FIG. 1. Schematic depiction of bioreactor test set up.

[0019] FIG. 2. Graph showing methane (biogas) production for in the presence or absence of hyperthermophilic pretreatment at retention times of 22.5 and 30 days.

[0020] FIG. 3. Graph showing hydrogen production for in the presence or absence of hyperthermophilic pretreatment at retention times of 22.5 and 30 days.

[0021] FIG. 4. Graph showing relative methane (biogas) production for chopped Sargasso seaweed subjected to hyperthermophilic pretreatment, chopped Sargasso seaweed without hyperthermophilic pretreatment, and a cellulose control.

[0022] FIG. 5. Graph showing relative methane (biogas) production for mixed agricultural waste subjected to hyperthermophilic pretreatment, mixed agricultural waste without hyperthermophilic pretreatment, and a cellulose control.

[0023] FIG. 6. Graph showing relative methane (biogas) production for papermill waste subjected to hyperthermophilic pretreatment, papermill waste without hyperthermophilic pretreatment, and a cellulose control.

[0024] FIG. 7. Graph showing relative methane (biogas) production for spent grains subjected to hyperthermophilic pretreatment, spent grains without hyperthermophilic pretreatment, and a cellulose control.

[0025] FIG. 8. Graph showing relative methane (biogas) production for barley straw subjected to hyperthermophilic pretreatment, barley straw without hyperthermophilic pretreatment, and a cellulose control.Detailed Description

[0026] The present invention provides systems and methods for increasing throughput and biogas production in a biogas reactor by pretreatment with hyperthermophilic organisms so that the retention time of biomass in the bioreactors can be decreased. Unexpectedly, the present inventors have found that utilization of a hyperthermophilic fermentation pretreatment step on biomass can both decrease the retention time needed for the pretreated biomass when introduced into a biogas reactor and increase total biogas production as compared to biomass substrates that are not pretreated with a hyperthermophilic pretreatment step. This synergistic effect allows for both increased throughput of biomass through a biogas reactor as well as increased total biogas production. This can greatly increase the efficiency of biogas plant with a given footprint. The technical effect is that more biomass can be moved through a biogas reactor over a given period of time and / or that the number of bioreactor units in an installation can be decreased.

[0027] Section headings as used in this section and the entire disclosure herein are merely for organizational purposes and are not intended to be limiting.1. Definitions

[0028] The terms “comprise(s),” “include(s),” “having,” “has,” “can,” “contain(s),” and variants thereof, as used herein, are intended to be open-ended transitional phrases, terms, or words that do not preclude the possibility of additional acts or structures. The singular forms “a,” “and” and “the” include plural references unless the context clearly dictates otherwise. The present disclosure also contemplates other embodiments “comprising,” “consisting of’ and “consisting essentially of,” the embodiments or elements presented herein, whether explicitly set forth or not.

[0029] For the recitation of numeric ranges herein, each intervening number there between with the same degree of precision is explicitly contemplated. For example, for the range of 6- 9, the numbers 7 and 8 are contemplated in addition to 6 and 9, and for the range 6.0-7.0, the number 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, and 7.0 are explicitly contemplated.

[0030] Unless otherwise defined herein, scientific, and technical terms used in connection with the present disclosure shall have the meanings that are commonly understood by those of ordinary skill in the art. The meaning and scope of the terms should be clear; in the event, however of any latent ambiguity, definitions provided herein take precedent over any dictionary or extrinsic definition. Further, unless otherwise required by context, singular terms shall include pluralities and plural terms shall include the singular.

[0031] As used herein, the term “biomass” refers to biological material which can be used as fuel, for energy production, or for industrial production. Most commonly, biomass refers to plant matter grown for use as biofuel, but it also includes plant or animal matter used for production of fibers, chemicals or heat. Biomass may also include biodegradable wastes that can be used as fuel. It is usually measured by dry weight. The term biomass is useful for plants, where some internal structures may not always be considered living tissue, such as the wood (secondary xylem) of a tree. This biomass became produced from plants that convert sunlight into plant material through photosynthesis. Sources of biomass energy lead to agricultural crop residues, energy plantations, and municipal and industrial wastes. The term “biomass,” as used herein, excludes components of traditional media used to culture microorganisms, such as purified starch, peptone, yeast extract but includes waste material obtained during industrial processes developed to produce purified starch. According to the invention, biomass may be derived from a single source, or biomass can comprise a mixturederived from more than one source; for example, biomass could comprise a mixture of corn cobs and corn stover, or a mixture of grass and leaves. Biomass includes, but is not limited to, bioenergy crops, agricultural residues, municipal solid waste, industrial solid waste, sludge from paper manufacture, cellulose and / or hemicellulose containing waste, yard waste, wood and forestry waste. Examples of biomass include, but are not limited to, corn grain, corn cobs, crop residues such as corn husks, corn stover, corn steep liquor, grasses, wheat, wheat straw, barley, barley straw, grain residue from barley degradation during brewing of beer, hay, rice straw, switchgrass, waste paper, sugar cane bagasse, sorghum, soy, components obtained from processing of grains, bees, branches, roots, leaves, wood chips, sawdust, shrubs and bushes, soybean hulls, vegetables, fruits, flowers and animal manure. In one embodiment, biomass that is useful for the invention includes biomass that has a relatively high carbohydrate value, is relatively dense, and / or is relatively easy to collect, transport, store and / or handle.

[0032] As used herein, the term “bioreactor” refers to an enclosed or isolated system for containment of a microorganism and a biomass material. The “bioreactor” may preferably be configured for anaerobic growth of the microorganism.

[0033] As used herein, the term “hyperthermophilic organism” means an organism which can grow at or above 80°C. It will be understood that hyperthermophilic organisms may be used for fermentations at temperatures above or below 80°C, or above or below the optimum temperature for the culture of the hyperthermophilic organism.

[0034] As used herein, the term hydraulic retention time (HRT) is defined as the average time interval over which substrate is kept in a reactor such as a digester. HRT may generally be expressed in units of time such as days or hours. See, e.g., Dong et al., Chapter 10 - Manure treatment and recycling technologies, in Circular Economy and Sustainability Volume 2: Environmental Engineering 2022, Pages 161-180

[0035] Preferred methods and materials are described below, although methods and materials similar or equivalent to those described herein can be used in practice or testing of the present disclosure. All publications, patent applications, patents and other references mentioned herein are incorporated by reference in their entirety. The materials, methods, and examples disclosed herein are illustrative only and not intended to be limiting.2. Biomass

[0036] The present invention contemplates the degradation of biomass with hyperthermophilic organisms. The present invention is not limited to the use of any particular biomass or organic matter. Suitable biomass and organic matter includes, but is notlimited to, sewage, agricultural waste products, brewery grain by-products, food waste, organic industry waste, forestry waste, crops, grass, seaweed, plankton, algae, fish, fish waste, corn potato waste, sugar cane waste, sugar beet waste, straw (e.g., wheat, rice, oat or barley straw), hay, fish sludge, fish manure, fish waste, paper mill waste, chicken manure, cow manure, hog manure, switchgrass, and marine or fresh water algas such as cyanobacteria (blue-green algae), green algae (division Chlorophyta), brown algae (Phaeophyceae, division Phaeophyta), and red algae (division Rhodophyta) and combinations thereof. In some embodiments, the biomass is harvested particularly for use in hyperthermophilic degradation processes, while in other embodiments waste or by-products materials from a pre-existing industry are utilized.

[0037] In some preferred embodiments, the biomass is lignocellulosic. In some embodiments, the biomass is pretreated with cellulases or other enzymes to digest the cellulose. In some embodiments, the biomass is pretreated by heating in the presence of a mineral acid or base catalyst to completely or partially hydrolyze hemicellulose, decrystallize cellulose, and remove lignin. This allows cellulose enzymes to access the cellulose.3. Hyperthermophilic organisms

[0038] The present invention contemplates the use of hyperthermophilic organisms for fermenting biomass in a pretreatment step before introduction into an anaerobic digester (bioreactor) for methane (biogas) production. The present invention is not limited to the use of any particular hyperthermophilic organism. In some embodiments, mixtures of hyperthermophilic organisms are utilized. In some embodiments, the hyperthermophiles are from the archaeal order Thermococcales, including but not limited to hyperthermophiles of the genera Pyrococcus, Thermococcus, and Palaeococcus. Examples of particular organisms within these genera include, but are not limited to, Pyrococcus furiosus, Thermococcus barophilus, T. aggregans, T. aegaeicus, T litoralis, T alcaliphilus, T. sibiricus, T atlanticus, T siculi, T pacificus, T. waiotapuensis, T zilligi, T. guaymasensis, T. fumicolans, T. gorgonarius, T celer, T. barossii, T. hydrothermalis, T. acidaminovorans, T. profundus, T. stetteri, T. kodakaraenis, T. peptonophilis. In some embodiments, aerobic hyperthermophilic organisms such as Aeropyrum pernix, Sulfolobus solfataricus, Metallosphaera sedula, Sulfolobus tokadaii, Sulfolobus shibatae, Thermoplasma acidophilum and Thermoplasma volcanium are utilized. While in other embodiments, anaerobic or facultative aerobic organisms such as Pyrobaculum calidifontis and Pyrobaculum oguniense are utilized. Other useful archaeal organisms include, but are not limited to, Sulfolobus acidocaldarius andAcidianus ambivalens. In some embodiments, the hyperthermophilic organisms are bacteria, such as Thermus aquaticus, Thermus thermophilus, Thermus flavus, Thermus ruber, Bacillus caldotenax, Geobacillus stearothermophilus, Anaerocellum thermophilus, Thermoactinomyces vulgaris, and members of the order Thermotogales, including, but not limited to Thermotoga elfeii, Thermotoga hypogea, Thermotoga maritima, Thermotoga neapolitana, Thermotoga subterranea, Thermotoga petrophila, Thermotoga thermarum, Petrotoga miotherma, Petrotoga mobilis, Thermosipho africanus, Thermosipho melanesiensis, Fervidobacterium islandicum, Fervidobacterium nodosum, Fervidobacterium pennavorans, Fervidobacterium gondwanense, Geotoga petraea, Geotoga subterranea. In some preferred embodiments, the microorganism preferably is a member of the genus Thermotoga.4. Methanogenic Organisms

[0039] In some preferred embodiments Methanogenic organisms are archaea from the genus such as Methanothrix, Methanosarcina, Methanomicrobium, Methanobrevibacter, Methanocalculus, Methanoculleus, Methanofollis, Methanobacterium, Methanoregula, Methanococcus, Methanospirillum, Methanocorpuscullum, Methanogenium, Methanimicrococcus, Methanosphaera, Methanothermobacter, Methanolinea, Methanomethylovorans, Methanomassiliicoccus, Methanosaeta. The genera of Methanogens occurring may vary depending on the substrate used in the AD reactor (Vftezova, M.;Kohoutova, A.; Vitez, T.; Hanisakova, N.; Kushkevych, I. Methanogenic Microorganisms in Industrial Wastewater Anaerobic Treatment. Processes 2020, 8, 1546. https: / / doi.org / 10.3390 / pr8121546; table 7 within this reference) or depending on the temperature of the AD (Krakat, N., Westphal, A., Satke, K., Schmidt, S. and Scherer, P. (2010), The microcosm of a biogas fermenter: Comparison of moderate hyperthermophilic (60°C) with thermophilic (55°C) conditions. Eng. Life Sci., 10: 520-527. See world wide web at doi.org / 10.1002 / elsc.201000064). Their might be also syntrophic fatty acid-oxidizing bacteria, living in syntropy with Methanogenic organisms like Syntrophomonas, Smithella, Leptolinea, Syntrophus, Pelobacter, Syntrophorhabdus, Syntrophomonadaceae and thus contributing to the methane production (Lim JW, Park T, Tong YW, Yu Z. The microbiome driving anaerobic digestion and microbial analysis. Advances in Bioenergy. 2020;5:1-61. doi: 10.1016 / bs.aibe.2020.04.001. Epub 2020 May 4. PMCID: PMC7198183.)5. Biogas production processes with reduced retention time and increased biogas production

[0040] In some preferred embodiments, the present invention provides processes where a biomass is subjected to a hyperthermophilic fermentation with a hyperthermophilic organism in a first bioreactor as a pretreatment step. The resulting pretreated biomass, which may preferably be in the form of a liquid fermentation broth, is then introduced into a second bioreactor populated with methanogenic organisms or a methane producing microbial consortium for biogas production. As discussed above, the retention time in the second bioreactor can be substantially reduced as compared to when a non-pretreated biomass is utilized while at the same time generating more biogas from the biomass.

[0041] Accordingly, in some preferred embodiments, the present invention provides an industrial scale process for producing biogas comprising: in a first bioreactor, fermenting a biomass with a population of at least one genus of a hyperthermophilic organism to provide a pretreated biomass; introducing the pretreated biomass into a second bioreactor having a volume of from 10m3to 20000 m3, and most preferably from 1000m3 to 20000 m3, and having therein a microbial consortium comprising methanogenic organisms; and fermenting the pretreated biomass in the second bioreactor to produce biogas under conditions such that 1) the hydraulic retention time of the pretreated biomass in the second bioreactor averages from 8 to 25 days; and / or 2) biogas is produced at the same and / or increased levels as compared to biogas production without hyperthermophilic pretreatment when the hydraulic retention time of the pretreated biomass in the second bioreactor averages from 8 to 25 days; and / or 3) biogas is produced at the same and / or increased levels as compared to biogas production without hyperthermophilic pretreatment when the hydraulic retention time of the pretreated biomass in the second bioreactor is reduced by from 20% to 80% as compared to the average retention time in a commercial biogas reactor.

[0042] The use of a wide variety of bioreactors, also known as biodigesters, is contemplated. Examples include, but are not limited to, floating drum digesters, fixed dome digesters, Deenbandhu digesters, bag digesters, plug flow digesters, anaerobic filters, upflow anaerobic sludge blankets, and pit storage digestors. Full-scale plants that are suitable for use in the present invention can be purchased from providers such as Hitachi Zosen Inova Schmack GmbH, Schwandorf, DE or Vorn Bioenergy, Regensburg, DE. These systems may be modified to accept introduction of a slurry or substrate (preferably containing acetate) from the hyperthermophilic bioreactors of the present invention. In some preferred embodiments, the methanogen bioreactor is in fluid communication with the hyperthermophilic bioreactor.

[0043] In some preferred embodiments, the hydraulic retention time of the pretreated biomass in the second bioreactor averages from 10 to 25 days, 15 to 25 days, 20 to 25 days, 10 to 22 days, 15 to 22 days, 10 to 20 days, 15 to 20 days, 8 to 22 days, 8 to 20 days or 8 to 15 days.

[0044] In some preferred embodiments, the hydraulic retention time of the pretreated biomass in the second bioreactor is reduced by from 20% to 70%, from 20% to 60%, from 20% to 50%, or from 20% to 40% as compared to the average retention time in a commercial biogas reactor.

[0045] In some preferred embodiments, the hydraulic retention time of the biomass in the first bioreactor averages from 4 to 24 hours, 5 to 16 hours, or 6 to 12 hours.

[0046] In some preferred embodiments, the volume of the second bioreactor is from 5000 m3to 20000 m3, 5000 m3to 15000 m3, 5000 m3to 12000 m3, 7000 m3to 20000 m3, 7000 m3to 15000 m3, 7000 m3to 12000 m3, 8000 m3to 20000 m3, 8000 m3to 15000 m3, or 8000 m3to 12000 m3.

[0047] In some preferred embodiments, the volume of the first bioreactor is from 10 m3to 10000 m3, and most preferably from 100 m3to 10000 m3.

[0048] In some preferred embodiments, the step of fermenting a biomass with a population of at least one genus of a hyperthermophilic organism to provide a pretreated biomass is performed at a temperature range of from 70.0 to 105.0°C, 70.0 to 100.0°C, 70.0 to 90.0°C, 70.0 to 85.0°C, 75.0 to 100.0°C, 75.0 to 90.0°C, 75.0 to 85.0°C, 76.0 to 84.0°C, 77.0 to 83.0°C, 78.0 to 82.0°C, 75.0 to 79.0°C, or 76.0 to 79.0°C.Examples

[0049] The following are examples of the present invention and are not to be construed as limiting.Example 1

[0050] This example provides data demonstrating that pretreatment of a biomass by hyperthermophilic fermentation reduces the retention time required when the biomass is subsequently introduced into a biogas reactor in pilot scale reactors. In addition to reduction in retention time, an increase in biogas production was observed as compared to fermentation in a biogas reactor alone (i.e., without hyperthermophilic pretreatment.

[0051] The process flow for this example is depicted in FIG. 1. As can be seen, the biomass (termed substrate is either subjected to hyperthermophilic pretreatment in a hyperthermophilic bioreactor followed by fermentation in a standard anaerobic biogas reactor (AD) or introduced directed into a standard anaerobic biogas reactor (control AD), bypassing the hyperthermophilic (HT) bioreactor. The conditions utilized in the reactors as well as measured parameters can be summarized as follows. The HT fermentation was conducted with a Thermotoga ssp.HT reactor• Filling volume: 225 1 (-> HRT = 9 h)• Pumping speed: 25 1 / h (600 1 / d)• Temperature: 79-80°C• H2 measurementHT-AD reactor• Filling volume: 18,000 1 (-> HRT = 30 d = 720 h) & 13,500 1 (-> HRT = 22.5 d = 540 h)• Pumping speed: 25 1 / h (600 1 / d)• Temperature: 52 °C• Biogas and CH4 measurementControl AD reactor• Filling volume: 700 1 (-> HRT = 30 d = 720 h)• Pumping speed: 0.97 1 / h (23.3 1 / d)• Temperature: 52 °C• Biogas and CH4 measurement

[0052] For the bypass test, substrate was pumped from a buffer tank directly to the respective AD reactors without including a hyperthermophilic fermentation step. The result is an 8-10% lower biogas production of the HT-AD than with the control AD. The reason for that is probably the different design of the reactors. Substrates utilized in the tests are described in the following tables.Substrate for bypass testSubstrate for reduced retention time test

[0053] Description 30 days retention time test. For this phase the HT pretreatment was performed with 9h retention time of the substrate in the HT reactor before pumping the material to the AD reactor. There the retention time was 30 days. See phases 0 & al & a2. There were changes in the substrate mix from phase 0 (decanter liquid) to phase al and a2 (both with pig manure instead of decanter liquid)

[0054] Description 22.5 days retention time test. For this phase the HT pretreatment was performed with 9h retention time of the substrate in the HT reactor before pumping the material to the AD reactor. There the retention time was 22.5days. See phases bl & b2 & b3. Three retention times were required to reach almost complete exchange of the old 30 days RT (Retention Time) substrate with 22.5 days material to clearly demonstrate the effect. The results are presented in FIGs. 2 and 3. FIG. 2 provides the biogas production results for 30 days RT (0, al, a2) and 22.5days RT (bl, b2, b3). The shift from phase a (HRT 30d) to phase b (HRT 22.5d) took place from day 88 to day 95. FIG. 3 provides the hydrogen production results. This data shows that biogas production increases when the biomass is subjected to HT pretreatment even when retention time is decreased in the biogas AD. See FIG. 2.Example 2

[0055] This example describes the impact of HT pretreatment in lab scale fermentations. Two or three liter batch fermentations at 80 °C were performed for the time indicated and followed by a small-scale biogas potential test.

[0056] FIG. 4 provides the results for a test utilizing chopped Sargasso seaweed as a substrate (either pretreated by HT fermentation with a Thermotoga ssp. (denoted FR221122- R2, 21 day fermentation in tap water) or untreated (denoted Sargasso chopped)) and cellulose as a control. The results show that biogas production of fermented material provided a higher peak within the first 10 days and that total biogas production is finished earlier than unfermented material and cellulose control.

[0057] FIG. 5 provides the results for a test utilizing mixed agricultural waste as a substrate (either pretreated by HT fermentation with a Thermotoga ssp. (denoted FR220405- 21, 3 day fermentation) or untreated (denoted mixed agricultural waste)) and cellulose as a control. The results show that biogas production of fermented material provided a higher peak within the first 5-6 days and that total biogas production is finished earlier than unfermented material and cellulose control.

[0058] FIG. 6 provides the results for a test utilizing paper mill waste as a substrate (either pretreated by HT fermentation with a Thermotoga ssp. (denoted FR220103-31, 7 day fermentation) or untreated (denoted paper mill waste)) and cellulose as a control. The results show that biogas production of fermented material provided a higher peak within the first 5-6 days and that total biogas production is finished earlier than unfermented material and cellulose control.Example 3

[0059] This example describes the impact of HT pretreatment in lab scale fermentations. Two liter batch fermentations at 80°C were performed for the time indicated and followed by a small-scale biogas potential test. FIG. 7 provides the results for a test utilizing spent grains as a substrate (either pretreated by HT fermentation with a Thermotoga ssp. (denoted FR240531-R4, 2.9 day fermentation in tap water) or untreated (denoted spent grains)) and cellulose as a control. The results show that biogas production of fermented material provided a higher peak within the first 10 days and that total biogas production is finished earlier than unfermented material and cellulose control.Example 4

[0060] FIG. 8 provides the results for a test utilizing barley straw as a substrate (either pretreated by HT fermentation (denoted FR240531-R3, 2,9 day fermentation) with a mix of strains (i.e., a consortium denoted FL3-L7b-2-4) including at least a strain of Thermotoga spp. or untreated (denoted barley straw)) and cellulose as a control. The results show that biogas production of fermented material provided a higher peak within the first 5-6 days andthat total biogas production is finished earlier than unfermented material and cellulose control.

[0061] The scope of the present invention is not limited by what has been specifically shown and described hereinabove. Those skilled in the art will recognize that there are suitable alternatives to the depicted examples of materials, configurations, constructions, and dimensions. Variations, modifications, and other implementations of what is described herein will occur to those of ordinary skill in the art without departing from the spirit and scope of the invention.

[0062] Numerous references, including patents and various publications, are cited and discussed in the description of this invention. The citation and discussion of such references is provided merely to clarify the description of the present invention and is not an admission that any reference is prior art to the invention described herein. All references cited and discussed in this specification are incorporated herein by reference in their entirety.

Claims

ClaimsWhat is claimed is:

1. An industrial scale process for producing biogas comprising: in a first bioreactor, fermenting a biomass with a population of at least one genus of a hyperthermophilic organism to provide a pretreated biomass; introducing the pretreated biomass into a second bioreactor having a volume of from 1000 m3to 20000 m3and having therein a microbial consortium comprising methanogenic organisms; fermenting the pretreated biomass in the second bioreactor to produce biogas under conditions such that 1) the hydraulic retention time of the pretreated biomass in the second bioreactor averages from 8 to 25 days; and / or 2) biogas is produced at the same and / or increased levels as compared to biogas production without hyperthermophilic pretreatment when the hydraulic retention time of the pretreated biomass in the second bioreactor averages from 8 to 25 days; and / or 3) biogas is produced at the same and / or increased levels as compared to biogas production without hyperthermophilic pretreatment when the hydraulic retention time of the pretreated biomass in the second bioreactor is reduced by from 20% to 80% as compared to the average retention time in a commercial biogas reactor.

2. The process of claim 1, wherein the hydraulic retention time of the pretreated biomass in the second bioreactor averages from 10 to 25 days, 15 to 25 days, 20 to 25 days, 10 to 22 days, 15 to 22 days, 10 to 20 days, 15 to 20 days, 8 to 22 days, 8 to 20 days or 8 to 15 days.

3. The process of claim 1, the hydraulic retention time of the pretreated biomass in the second bioreactor is reduced by from 20% to 70%, from 20% to 60%, from 20% to 50%, or from 20% to 40% as compared to the average retention time in a commercial biogas reactor.

4. The process of any one of claims 1 to 3, wherein the hydraulic retention time of the biomass in the first bioreactor averages from 4 to 24 hours, 5 to 16 hours, or 6 to 12 hours.

5. The process of any one of claims 1 to 4, wherein the volume of the second bioreactor is from 5000 m3to 20000 m3, 5000 m3to 15000 m3, 5000 m3to 12000 m3, 7000 m3to 20000m3, 7000 m3to 15000 m3, 7000 m3to 12000 m3, 8000 m3to 20000 m3, 8000 m3to 15000 m3, or 8000 m3to 12000 m3.

6. The process of any one of claims 1 to 4, wherein the volume of the first bioreactor is from 10 m3to 10000 m3, and most preferably from 1000 m3to 10000 m3.

7. The process of any one of claims 1 to 6, wherein the biomass is selected from the group consisting of sewage, agricultural waste products, brewery grain by-products, food waste, forestry waste, crops, grass, seaweed, plankton, algae, fish, fish waste, corn, potato waste, sugar cane waste, sugar beet waste, straw, paper waste, chicken manure, fish manure, fish sludge, cow manure, hog manure, switchgrass and combinations thereof.

8. The process of any one of claims 1 to 7, wherein the at least one genus of a hyperthermophilic organism is selected from the group consisting of the genera Pyrococcus, Thermococcus, Acidianus, Palaeococcus, Thermoplasma, Pyrobaculum, Pyrolobus, Pyrodictium, Methanotehrmus, Methanopyrus, Fervidobacterium, Thermotoga, and combinations thereof.

9. The process of claim 8, wherein the at least one genus of a hyperthermophilic organism is Thermotoga.

10. The process of any one of claims 1 to 9, wherein the step of fermenting a biomass with a population of at least one genus of a hyperthermophilic organism to provide a pretreated biomass is performed at a temperature range of from 70.0 to 105.0°C, 70.0 to 100.0°C, 70.0 to 90.0°C, 70.0 to 85.0°C, 75.0 to 100.0°C, 75.0 to 90.0°C, 75.0 to 85.0°C, 76.0 to 84.0°C, 77.0 to 83.0°C, 78.0 to 82.0°C, 75.0 to 79.0°C, or 76.0 to 79.0°C.

11. The process of any one of claims 1 to 10, wherein the step of fermenting a biomass with a population of at least one genus of a hyperthermophilic organism to provide a pretreated biomass comprises fermentation in the presence of a cell density of the at least one genus of a hyperthermophilic organism of greater than 109cell / ml.

12. The process of any one of claims 1 to 11, further comprising removing the biogas from the second bioreactor.

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