EP3001844A1 - Procédé de fermentation régulée par le ph et de production de biogaz - Google Patents

Procédé de fermentation régulée par le ph et de production de biogaz

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Publication number
EP3001844A1
EP3001844A1 EP14729850.9A EP14729850A EP3001844A1 EP 3001844 A1 EP3001844 A1 EP 3001844A1 EP 14729850 A EP14729850 A EP 14729850A EP 3001844 A1 EP3001844 A1 EP 3001844A1
Authority
EP
European Patent Office
Prior art keywords
organic material
organic
biogas
anaerobic
lime pressure
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP14729850.9A
Other languages
German (de)
English (en)
Inventor
Frank Ulrik ROSAGER
Stefan Borre-Gude
Anders Peter Jensen
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
NGF Nature Energy Biogas AS
Original Assignee
XERGI NIX TECHNOLOGY AS
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by XERGI NIX TECHNOLOGY AS filed Critical XERGI NIX TECHNOLOGY AS
Publication of EP3001844A1 publication Critical patent/EP3001844A1/fr
Withdrawn legal-status Critical Current

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12P—FERMENTATION OR ENZYME-USING PROCESSES TO SYNTHESISE A DESIRED CHEMICAL COMPOUND OR COMPOSITION OR TO SEPARATE OPTICAL ISOMERS FROM A RACEMIC MIXTURE
    • C12P5/00—Preparation of hydrocarbons or halogenated hydrocarbons
    • C12P5/02—Preparation of hydrocarbons or halogenated hydrocarbons acyclic
    • C12P5/023—Methane
    • C—CHEMISTRY; METALLURGY
    • C05—FERTILISERS; MANUFACTURE THEREOF
    • C05F—ORGANIC FERTILISERS NOT COVERED BY SUBCLASSES C05B, C05C, e.g. FERTILISERS FROM WASTE OR REFUSE
    • C05F17/00—Preparation of fertilisers characterised by biological or biochemical treatment steps, e.g. composting or fermentation
    • C05F17/50—Treatments combining two or more different biological or biochemical treatments, e.g. anaerobic and aerobic treatment or vermicomposting and aerobic treatment
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12M—APPARATUS FOR ENZYMOLOGY OR MICROBIOLOGY; APPARATUS FOR CULTURING MICROORGANISMS FOR PRODUCING BIOMASS, FOR GROWING CELLS OR FOR OBTAINING FERMENTATION OR METABOLIC PRODUCTS, i.e. BIOREACTORS OR FERMENTERS
    • C12M21/00—Bioreactors or fermenters specially adapted for specific uses
    • C12M21/04—Bioreactors or fermenters specially adapted for specific uses for producing gas, e.g. biogas
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12M—APPARATUS FOR ENZYMOLOGY OR MICROBIOLOGY; APPARATUS FOR CULTURING MICROORGANISMS FOR PRODUCING BIOMASS, FOR GROWING CELLS OR FOR OBTAINING FERMENTATION OR METABOLIC PRODUCTS, i.e. BIOREACTORS OR FERMENTERS
    • C12M29/00—Means for introduction, extraction or recirculation of materials, e.g. pumps
    • C12M29/24—Recirculation of gas
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12M—APPARATUS FOR ENZYMOLOGY OR MICROBIOLOGY; APPARATUS FOR CULTURING MICROORGANISMS FOR PRODUCING BIOMASS, FOR GROWING CELLS OR FOR OBTAINING FERMENTATION OR METABOLIC PRODUCTS, i.e. BIOREACTORS OR FERMENTERS
    • C12M45/00—Means for pre-treatment of biological substances
    • C12M45/02—Means for pre-treatment of biological substances by mechanical forces; Stirring; Trituration; Comminuting
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12M—APPARATUS FOR ENZYMOLOGY OR MICROBIOLOGY; APPARATUS FOR CULTURING MICROORGANISMS FOR PRODUCING BIOMASS, FOR GROWING CELLS OR FOR OBTAINING FERMENTATION OR METABOLIC PRODUCTS, i.e. BIOREACTORS OR FERMENTERS
    • C12M45/00—Means for pre-treatment of biological substances
    • C12M45/06—Means for pre-treatment of biological substances by chemical means or hydrolysis
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12M—APPARATUS FOR ENZYMOLOGY OR MICROBIOLOGY; APPARATUS FOR CULTURING MICROORGANISMS FOR PRODUCING BIOMASS, FOR GROWING CELLS OR FOR OBTAINING FERMENTATION OR METABOLIC PRODUCTS, i.e. BIOREACTORS OR FERMENTERS
    • C12M45/00—Means for pre-treatment of biological substances
    • C12M45/20—Heating; Cooling
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12P—FERMENTATION OR ENZYME-USING PROCESSES TO SYNTHESISE A DESIRED CHEMICAL COMPOUND OR COMPOSITION OR TO SEPARATE OPTICAL ISOMERS FROM A RACEMIC MIXTURE
    • C12P7/00—Preparation of oxygen-containing organic compounds
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E50/00—Technologies for the production of fuel of non-fossil origin
    • Y02E50/30—Fuel from waste, e.g. synthetic alcohol or diesel
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/10—Process efficiency
    • Y02P20/133—Renewable energy sources, e.g. sunlight
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/141—Feedstock
    • Y02P20/145—Feedstock the feedstock being materials of biological origin
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/50—Improvements relating to the production of bulk chemicals
    • Y02P20/59—Biological synthesis; Biological purification
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
    • Y02W30/00—Technologies for solid waste management
    • Y02W30/40—Bio-organic fraction processing; Production of fertilisers from the organic fraction of waste or refuse

Definitions

  • the present invention is in the field of biomass processing and bioenergy production.
  • the present invention aims to increase the amount of biogas one can produce when processing organic material.
  • Biomass represents one source of renewable energy.
  • biomass energy is to have a long-term, commercial future, the organic material must be processed to generate affordable, clean and efficient energy forms, such as liquid and gaseous fuels, or electricity.
  • Biomass processing remains important to ensure an efficient exploitation of the biomass energy.
  • the energy potential can often be difficult to exploit and it can be present in a form which may only be exploited following extensive processing of the biomass.
  • An increased exploitation of the energy potential of a biomass may result in an increased production of renewable energy sources, such as biogas.
  • one challenge is to extract as much energy as possible from the biomass, by use of as little energy as possible, in order to increase the total energy yield of the process.
  • the present invention aims to secure this objective. Summary of the Invention
  • the present invention facilitates efficient biomass processing and an increased production of renewable energy from processing and anaerobic fermentation of a wide variety of organic materials.
  • organic materials have a high energy potential which can be exploited by processing the organic material.
  • One form of processing an organic material is by performing an anaerobic fermentation resulting in the production of biogas. This process represents a conversion of an energy potential to a readily usable energy source.
  • Pre-treatment of biomasses - including lime pressure cooking - and partial stripping of ammonia N prior to performing a biogas fermentation is not always sufficient to preclude an undesirable inhibition of biogas producing bacteria by ammonia released from organic bound N not stripped during the pre-treatment step.
  • a dual fermentation method for generating biogas from anaerobic fermentation of processed organic material comprising solid and liquid parts, said method comprising the steps of i) subjecting an organic material comprising one or more sources of nitrogen to a facultative anaerobic fermentation resulting in at least partial hydrolysis of the organic material and at least partial conversion of organic N (nitrogen) present in the organic material to inorganic N, and wherein essentially no biogas is produced; subjecting the organic material fermented in step i) to lime pressure cooking, wherein the lime-pressure cooking results in a further hydrolysis of said organic material, and wherein said lime pressure cooking step results in the conversion of inorganic N to ammonia fluids which are diverted from the lime pressure cooker and thereby separated from the organic material; iii) subjecting the organic material fermented in step i) and subjected to lime pressure cooking in step ii) to a strictly anaerobic fermentation resulting in the production of biogas under conditions where
  • the pre-incubated and lime pressure cooked organic material is diverted from said lime pressure cooker to a buffer tank and the pH value of the pre-incubated and lime pressure cooked organic material is lowered by contacting the pre-incubated and lime pressure cooked organic material with with a carbon dioxide (C0 2 ) containing gas.
  • the lowering of the pH value of the pre-incubated and lime pressure cooked organic material in the buffer tank can be assisted by the addition of an acid, such as an organic or inorganic acid, to the organic material.
  • the diversion to the buffer tank of C0 2 containing gas, or an organic or inorganic acid controls the pH of the organic material diverted to the buffer tank.
  • the pH of the organic material diverted to the buffer tank is typically above 8.5 when the organic material is initially received from the lime pressure cooker, and it is generally preferred to maintain the pH of the organic material present in the buffer tank within a pH value of from preferably 7.0 to 8.2.
  • a pH value of from 7.0 to 8.2 is also preferred in the anaerobic digester in which the strictly anaerobic fermentation resulting in the production of biogas is conducted under conditions wherein the pH level is kept within this predetermined pH range in order to reduce the conversion of NH 4 + to NH 3 as NH 3 is an inhibitor of methanogenic microorganisms.
  • a method for generating biogas from an anaerobic fermentation of processed organic material comprising solid and liquid parts, said method comprising the steps of i) diverting a first organic material comprising one or more sources of nitrogen to a pre-incubation tank and subjecting said organic material to a mineralisation by chemical and/or biological means, wherein the mineralisation results in the conversion of organic N (nitrogen) present in the organic material to inorganic N; ii) diverting the pre-incubated first organic material to a lime pressure cooker and subjecting said first pre-incubated organic material to lime pressure cooking, wherein said lime pressure cooking step results in the formation of ammonia fluids which are diverted from the pressure cooker and thereby separated from the organic material present in the lime pressure cooker; and iii) diverting pre-incubated and lime pressure cooked organic material from said lime pressure cooker to a buffer tank and lowering the pH value of the pre- incubated and lime pressure cooked material in the buffer tank.
  • the method may comprise the further step of
  • the pre-incubated and lime pressure cooked organic material may be mixed in the buffer tank with a further organic material; wherein the further organic material preferably has not been subjected to lime pressure cooking prior to the mixing with the lime pressure cooked organic material.
  • the pH value of the pre-incubated and lime pressure cooked organic material which is diverted from the lime pressure cooker to the buffer tank is lowered in the buffer tank by contacting the pre-incubated and lime pressure cooked organic material in the buffer tank with a carbon dioxide (C0 2 ) containing gas.
  • the lowering of the pH value of the organic material in the buffer tank may optionally be assisted by the addition of an acid to the organic material.
  • the carbon dioxide (C0 2 ) containing gas diverted to the organic material in the buffer tank can be biogas diverted to the buffer tank from an anaerobic fermenter which is receiving as input biomass material the organic material present in the buffer tank.
  • the diversion to the buffer tank of C0 2 containing gas controls the pH of the organic material present in the buffer tank.
  • the pH of the organic material diverted to the buffer tank is typically above 8.5 when initially received from the lime pressure cooker, and it is generally preferred to maintain the pH of the organic material present in the buffer tank within a pH value of from preferably 7.0 to 8.2.
  • a pH value of from 7.0 to 8.2 is also preferred in the anaerobic digester in which the strictly anaerobic fermentation resulting in the production of biogas is conducted under conditions wherein the pH level is kept within this predetermined pH range.
  • This pH interval is preferred in order to reduce the conversion of NH 4 + to NH 3 as NH 3 is an inhibitor of methanogenic microorganisms.
  • the optionally mixed, organic material(s) are diverted from the buffer tank to at least one, anaerobic biogas fermenter suitable for conducting an anaerobic, bacterial digestion of the organic material, wherein the anaerobic, bacterial digestion results in the generation of biogas by fermenting, under anaerobic fermentation conditions, the organic material diverted to the anaerobic biogas fermenter from the buffer tank, and collecting the biogas resulting from said anaerobic fermentation of said organic material.
  • a method for generating biogas from an anaerobic fermentation of processed organic material including solid and liquid parts, includes i) diverting a first organic material comprising one or more sources of nitrogen to a lime pressure cooker; ii) subjecting said first organic material to a lime pressure cooking step resulting in at least partly hydrolysing said first organic material comprising one or more sources of nitrogen, wherein said lime pressure cooking step results in the formation of ammonia fluids; iii) diverting said ammonia fluids formed in the lime pressure cooker to an absorption unit; iv) absorbing and condensing ammonia fluids diverted to the absorption unit from the lime pressure cooker; v) diverting lime pressure cooked organic material from said lime pressure cooker to a buffer tank; vi) mixing lime pressure cooked organic material with a further organic material in the buffer tank; vii) contacting the mixed, organic materials with a C0 2 containing gas, such as e.g.
  • a method for generating biogas from an anaerobic fermentation of processed organic material comprising solid and liquid parts, said method comprising the steps of i) diverting a first organic material comprising one or more sources of nitrogen to a pre-incubation tank and subjecting said organic material to a mineralisation by chemical and/or biological means, wherein the mineralisation results in the conversion of organic N (nitrogen) present in the organic material to inorganic
  • a method for generating biogas from an anaerobic fermentation of processed organic material comprising solid and liquid parts, said method comprising the steps of i) diverting a first organic material comprising one or more sources of nitrogen to a pre-incubation tank and subjecting said organic material to a mineralisation by chemical and/or biological means, wherein the
  • mineralisation results in the conversion of organic N (nitrogen) present in the organic material to inorganic N; ii) diverting the pre-incubated first organic material to a lime pressure cooker and subjecting said first pre-incubated organic material to lime pressure cooking, wherein said lime pressure cooking step results in the formation of ammonia fluids; iii) diverting pre-incubated and lime pressure cooked organic material from said lime pressure cooker to a buffer tank and lowering the pH value of the pre- incubated and lime pressure cooked material in the buffer tank.
  • the present invention generally provides improved methods for processing organic biomass materials, converting organic nitrogen (N) fractions, including protein N and uric acid, into inorganic nitrogen (N) fractions by mineralization, removing by stripping or extraction inorganic nitrogen (N) by subjecting the organic biomass materials to a temperature and pH which allow gaseous ammonia to be stripped or extracted, thereby reducing the contents of inorganic nitrogen (N) fractions, including ammonia, which would otherwise cause an inhibitory effect in a subsequent, anaerobic biogas fermentation, and, as a result of reducing said inorganic nitrogen (N) fractions from the organic biomass to be subjected to anaerobic biogas fermentation, increasing the production of biogas when performing the anaerobic biogas fermentation on the organic biomass having reduced contents of otherwise inhibitory, or potentially inhibitory, organic and/or inorganic nitrogen (N) fractions.
  • the methods of the present invention can achieve one or more of the below-cited technical effects in respect of the processing of an organic biomass material prior to subjecting the biomass material to an anaerobic biogas fermentation.
  • TAN total ammonia N
  • thermo-chemical lime pressure cooking step it is also possible, in accordance with the methods of the present invention, to strip at least approximately 65%, such as at least approximately 70%, for example at least approximately 75%, such as at least approximately 80%, for example at least approximately 85%, of the total ammonia N TAN during the (NiX) nitrogen extracting, thermo-chemical lime pressure cooking step.
  • a plant for generating biogas from an anaerobic fermentation of processed organic material including solid and liquid parts.
  • the plant includes i) a lime pressure cooker for hydrolysing a first organic material comprising one or more sources of nitrogen; ii) an absorption unit for absorbing and condensing ammonia fluids diverted to the absorption unit from the lime pressure cooker when said first organic material is subjected to lime pressure cooking; iii) a buffer tank for mixing lime pressure cooked organic material with a further organic material prior to diverting the mixed, organic materials to one or more fermenters; iv) one or more fermenters for anaerobically fermenting said organic materials diverted to said one or more fermenters from said buffer tank, wherein said fermentation results in the generation of biogas; v) a separation unit for separating organic materials diverted to the separation unit from said one or more fermenters, wherein said separation of said organic materials results in the generation of a solid organic material fraction and a liquid fraction compris
  • FIGS 1 to 24 illustrate various alternative embodiments of the present invention in which organic biomass and re-circulated liquid from an anaerobic digester (biogas fermenter(s)) are diverted to a lime pressure cooking step (NiX treatment) and lime (CaO / Ca(OH) 2 is added to create - at a temperature of more than 100°C and a pressure of more than 1 bar - a pH suitable for converting ammonium N (NH 4 + ) to gaseous ammonia (NH 3 ) - which can be stripped, collected e.g. in an ammonia scrubber, and converted into ammonium sulphate - which can subsequently be used as a fertilizer.
  • the lime pressure cooked biomass is diverted to a buffer tank - prior to being diverted into one, or a series of at least two, connected anaerobic digesters for the production of biogas.
  • Additional biomass may be mixed with the lime pressure cooked biomass in the buffer tank.
  • a conversion of organic nitrogen to ammonium N may take place in the buffer tank - and the generated ammonium N (NH 4 + ) may subsequently be converted to gaseous ammonia (NH 3 ) under suitable conditions.
  • a separation of fiber i.e. solid fraction, "spent biomass", also known as the digestate
  • liquid phase takes place and the liquid fraction can be diverted (i.e. re-circulated) back to the lime pressure cooker.
  • a C0 2 containing gas such as e.g.
  • FIGS 1 to 6 illustrate a plant and a process as described herein above in which a preincubation step has been inserted prior to Nix treatment / lime pressure cooking. Under suitable conditions, the biomass is being converted into more basic constituents, i.e. fx peptides, saccharides and fatty acids, chemically and/or biologically under anaerobic and/or aerobic conditions, and organic N - i.e.
  • organic nitrogen bound in and forming part of the biomass is subsequently mineralised and converted into ammonium N (NH 4 + ) - which in turn, again under suitable conditions, can be converted into gaseous ammonia (NH 3 ).
  • these two supplementary pre-treatment steps may aid significantly in the conversion / mineralisation of organic nitrogen to inorganic nitrogen - i.e. what is also termed N-mineralization.
  • ammonia is being stripped from the lime pressure cooker only.
  • a C0 2 containing gas is being added or injected into the organic biomaterial present in the buffer tank.
  • a C0 2 containing gas preferably biogas, is being added or injected into the organic biomaterial present in the anaerobic digester.
  • a C0 2 containing gas is being added or injected into the organic biomaterial present in the buffer tank as well as into the anaerobic digester.
  • the addition or injection of the C0 2 containing gas is aimed at controlling the pH value of the organic biomass as explained herein below in the detailed description as well as in the examples.
  • FIGs 4 to 6 illustrate the embodiments illustrated in Figures 1 to 3 with the addition of further organic biomass to the anaerobic digester.
  • the buffer tank (not illustrated).
  • Figures 7 to 12 illustrate embodiments in which an addition of lime to the pre-incubation tank is performed in order to increase the conversion of organic N to ammonium N (NH 4 + ) - and to shift the equilibrium between ammonium N (NH 4 + ) and gaseous ammonia (NH 3 ) in the direction of gaseous ammonia (NH 3 ) - with a view to stripping gaseous ammonia (NH 3 ) also during the pre-incubation phase. Additional lime may be added during the lime pressure cooking step (not shown).
  • ammonia is being stripped not only from the lime pressure cooker, but also from the pre-incubation tank.
  • a C0 2 containing gas is being added or injected into the organic biomaterial present in the buffer tank.
  • a C0 2 containing gas preferably biogas, is being added or injected into the organic biomaterial present in the anaerobic digester.
  • a C0 2 containing gas is being added or injected into the organic biomaterial present in the buffer tank as well as into the anaerobic digester.
  • Figures 13 to 18 illustrate embodiments in which ammonia is stripped from the buffer tank following NiX treatment (i.e. lime pressure cooking) - in addition to being stripped during the lime pressure cooking step (i.e. nitrogen extraction - NiX treatment).
  • NiX treatment i.e. lime pressure cooking
  • Figures 13 to 18 illustrate embodiments in which ammonia is stripped from the buffer tank following NiX treatment (i.e. lime pressure cooking) - in addition to being stripped during the lime pressure cooking step (i.e. nitrogen extraction - NiX treatment).
  • ammonia is being stripped not only from the lime pressure cooker, but also from the buffer tank.
  • a C0 2 containing gas is being added or injected into the organic biomaterial present in the buffer tank.
  • a C0 2 containing gas preferably biogas, is being added or injected into the organic biomaterial present in the anaerobic digester.
  • a C0 2 containing gas is being added or injected into the organic biomaterial present in the buffer tank as well as into the anaerobic digester.
  • the addition or injection of the C0 2 containing gas is aimed at controlling the pH value of the organic biomass as explained herein below in the detailed description as well as in the examples.
  • FIGs 16 to 18 illustrate the embodiments illustrated in Figures 13 to 15 with the addition of further organic biomass to the anaerobic digester.
  • the buffer tank (not illustrated).
  • FIGs 19 to 24 illustrate embodiments in which gaseous ammonia (NH 3 ) is stripped from each and all of the pre-incubation tank, the lime pressure cooker (NiX treatment) and the buffer tank. It is illustrated that lime (CaO) is added to the pre-incubation tank, but additional lime may be added to the lime pressure cooker, if needed.
  • the operational conditions as well as the chemical reaction conditions are different for the pre-incubation tank and for the lime pressure cooker as described herein below in more detail.
  • ammonia is being stripped not only from the lime pressure cooker, but also from the pre-incubation tank prior to lime pressure cooking, and from the buffer tank following the lime pressure cooking step.
  • a C0 2 containing gas is being added or injected into the organic biomaterial present in the buffer tank in order to control the pH.
  • a C0 2 containing gas preferably biogas, is being added or injected into the organic biomaterial present in the anaerobic digester.
  • a C0 2 containing gas is being added or injected into the organic biomaterial present in the buffer tank as well as into the anaerobic digester.
  • Figure 25 illustrates a time response curve for pH neutralisation of a lime pressure cooked (NiX treated) organic biomass material.
  • Figure 26 illustrates expected methane production in a two-stage CSTR with a thermophilic primary digester and a mesophilic secondary digester, both with 15 days retention time in accordance with the Example 3.
  • Bt methane yield after time t. Error bars are produced from 95% confidence intervals (see Fig. 28 and Table 7);
  • Figure 27 illustrates Retford hen litter in accordance with the Example 3.
  • Figure 28 illustrates specific methane yield from batch bottles with Hen litter in accordance with the Example 3. Errorbars equal 1x the standard deviation. B(t) - measured methane yield.
  • Figure 29 illustrates specific methane yield per kg chicken litter VS added (5 days rolling average) in accordance with the Example 4.
  • Figure 30 illustrates TAN and NH3 concentrations in the digester in accordance with the Example 4.
  • FIG 31 illustrates pH in the digester in accordance with the Example 4.
  • FIG. 32 illustrates VFA in the digester in accordance with the Example 4.
  • Figure 33 illustrates Blow-up of C4-C5 VFA in the digester in accordance with the Example 4
  • Figure 34 illustrates TS in digester and recycled liquid in accordance with the Example 4;
  • Figure 35 illustrates specific methane yield per kg chicken litter VS added (5 days rolling average) in accordance with the Example 4.
  • Figure 36 illustrates TAN and NH 3 concentrations in the digester in accordance with the Example 4.
  • Figure 37 illustrates pH in the digester in accordance with the Example 4;
  • Figure 38 illustrates VFA in the digester in accordance with the Example 4;
  • Figure 39 illustrates Blow-up of C4-C5 VFA in digester in accordance with the Example 4;
  • Figure 40 illustrates TS in digester and recycled liquid in accordance with the Example 4.
  • Figure 41 illustrates specific methane yield per kg chicken litter VS added (5 days rolling average) in accordance with the Example 4;
  • Figure 42 illustrates TAN and NH 3 concentrations in the digester in accordance with the Example 4.
  • FIG 43 illustrates pH in the digester in accordance with the Example 4.
  • Figure 45 illustrates Blow-up of C4-C5 VFA in digester in accordance with the Example 4
  • Figure 46 illustrates TS in the digester and recycled liquid in accordance with the Example 4;
  • Figure 47 illustrates specific methane yield per kg chicken litter VS added (5 days rolling average) in accordance with the Example 4;
  • Figure 48 illustrates TAN and NH3 concentrations in the digester in accordance with the Example 4;
  • Figure 49 illustrates pH in the digester in accordance with the Example 4;
  • Figure 50 illustrates VFA in digester in accordance with the Example 4
  • Figure 51 illustrates Blow-up of C4-C5 VFA in digester in accordance with the Example 4;
  • Figure 52 illustrates TS in digester and recycled liquid in accordance with the Example 4.
  • Figure 53 illustrates TAN and NH 3 concentrations in the digester in accordance with the Example 4.
  • Figure 54 illustrates pH in the digester in accordance with the Example 4.
  • Figure 55 illustrates TAN and NH 3 concentrations in the digester in accordance with the Example 4.
  • Figure 56 illustrates pH in the digester in accordance with the Example 4.
  • Figure 57 illustrates specific methane yield per kg chicken litter VS added (7 day rolling average) in accordance with the Example 4;
  • Figure 58 illustrates VFA in digester in accordance with the Example 4.
  • Figure 59 illustrates TS in digester and recycled liquid in accordance with the Example 4.
  • Figure 61 illustrates expected methane yields of broiler litter in a CSTR setup in accordance to the Example 5.
  • B t Methane yield at time t.
  • Blue bar Methane yield in a primary thermophilic reactor with 15 days retention time.
  • Dark-red bar Methane yield in a secondary mesophilic reactor also with a 15 day retention time.
  • Purple bar Total methane yield in both reactors;
  • Figure 62 illustrates accumulated methane yield from BMP setup 1 with untreated, mineralised and NiX treated chicken litter in accordance with the Example 5. Errorbars represent 95% confidence intervals;
  • Figure 63 illustrates accumulated methane yield from BMP setup 2 with untreated, mineralised, NiX treated and pH adjusted chicken litter in accordance with the Example 5. Errorbars represent 95% confidence intervals;
  • Figure 64 illustrates precipitated material during pH neutralisation of organic biomass using
  • Lime pressure cooking is an example of a pre-treatment processing step resulting in nitrogen extraction - a technical term often abbreviated "NiX" (cf. Figures 1 to 24).
  • Lime pressure cooking is in principle conducted at temperatures above 100°C and at a pressure of above 1 bar.
  • Lime pressure cooking results in the conversion of inorganic ammonia N (MH 4 + ) to gaseous ammonia (NH 3 ) as illustrated in Figures 1 to 24.
  • the term pre-treatment signifies that this processing step occurs prior to the step of anaerobic digestion and the production of biogas.
  • the pH of the treated biomaterial is increased by adding (burnt) lime (CaO) to the biomaterial.
  • Addition of lime facilitates a reduction in the TAN pool by facilitating a removal of ammonia fluids. This is a necessary step in order to obtain high ammonia removal efficiencies (see
  • Equation 1 2NHt ⁇ aq) + 20H( aq) 2NH 3 ⁇ g + 2H 2 0 ⁇ 1
  • ammonia exerts an inhibitory effect on the microorganisms responsible for fermenting the biomaterial and producing the biogas
  • ammonia can be regarded as an undesirable part of the TAN (total ammonium Nitrogen) pool, and any residual alkaline constituents present in the anaerobic digester is likely to counteract the benefits of the TAN removal obtained by performing a NiX treatment / lime pressure cooking.
  • the present invention solves the above-cited disadvantages by lowering the pH of the biomaterial present in a buffer tank prior to anaerobic digestion, or by lowering the pH of the biomaterial present in the anaerobic digester itself.
  • the solution involves one or more step(s) associated with injecting a carbon dioxide containing gas (C0 2(g) ) - such as e.g. biogas, which contain carbon dioxide in amounts relevant for the purpose of and practical solution provided by the present invention - through the NiX treated / lime pressure cooked biomaterial either when the NiX treated / lime pressure cooked biomaterial is present in a buffer tank following lime pressure cooking, and/or when the NiX treated / lime pressure cooked biomaterial has subsequently been diverted to the anaerobic digester.
  • C0 2( g ) can be converted to carbonic acid (H 2 C0 3(a q ) ) if it reacts with water, and this will lead to a neutralisation of exogenous base.
  • the present invention demonstrates that it is possible to lower the pH of a biomaterial by injecting C0 2( g ) containing fluids into the biomaterial following NiX treatment / lime pressure cooking, and that calcium can be precipitated as calcium carbonate (CaC0 3(S) ) during the neutralisation reaction.
  • the residual Ca 2+ ions have a potential - through the formation of H 2 C0 3( aq ) - to drive the pH level below that of the original pH level of the biomaterial.
  • the formation of the ammonia fraction of the TAN pool is pH dependent and one advantage of acidifying the NiX treated / lime pressure cooked biomaterial is that this in itself creates the possibility of reducing the amount of biomaterial that will have to be NiX treated / lime pressure cooked.
  • the acidification of the biomaterial by injection of C0 2(g) containing fluids can be performed in a buffer tank following the lime pressure cooking step. This is illustrated e.g. in the embodiments illustrated in the enclosed figures 1 , 3, 4, 6, 7, 9, 10, 12, 13, 15, 16, 18, 19, 21 , 22, and 24.
  • C0 2(g) containing fluids can be injected into a biomaterial present in an anaerobic digester - to which the optionally C0 2( g ) treated biomaterial in the buffer tank can be diverted.
  • the acidification of the biomaterial by injection of C0 2(g) containing fluids can be performed directly in an anaerobic digester following diversion of biomaterial from the buffer tank to the anaerobic digester. This is illustrated e.g. in the embodiments illustrated in the enclosed figures 2, 3, 5, 6, 8, 9, 1 1 , 12, 14, 15, 17, 18, 20, 21 , 23 and 24.
  • Diversion of C0 2( g ) containing fluids, including diversion of biogas, to one or more biomaterials in both in the buffer tank as well as in the anaerobic digester is illustrated in figures 3, 6, 9, 12, 15, 18, 21 and 24.
  • the pH value of the organic biomaterial diverted to the anaerobic biogas fermenter can be maintained within a predetermined pH-range by contacting the organic material present in the anaerobic biogas fermenter e.g. with re-circulated biogas, or a biogas diverted to the anaerobic biogas fermenter from an external source, wherein said contacting results in said pH value of the biomaterial being maintained within a predetermined pH-range. It is also possible to obtain an additional contribution to the lowering of the pH value of the biomaterial present in the buffer tank.
  • At least part of a liquid organic material fraction comprising one or more sources of nitrogen selected from organic nitrogen sources and inorganic nitrogen sources and obtained by separation of the liquid fraction from a solid fraction following anaerobic digestion and biogas production can be diverted to the buffer tank, wherein said diversion of said liquid organic material fraction results in, or contributes to, lowering the pH-value of the pre- incubated and lime pressure cooked organic material present in the buffer tank.
  • the pH value of the pre-incubated material subjected to lime pressure cooking in the lime pressure cooker decreases over time due to the stripping of gaseous ammonia.
  • the pH value in the buffer tank of the pre-incubated and lime pressure cooked organic material will be lower than the pH value of the pre-incubated and lime pressure cooked organic material present in the lime pressure cooker because of the addition or diversion to the buffer tank of pH lowering means.
  • the lowering of the pH value of the lime pressure cooked organic material present in the buffer tank can be obtained i) by contacting said organic material in the buffer tank with a C0 2 containing gas, such as biogas, and/or ii) by contacting said organic material in the buffer tank with an acid selected from an organic acid and an inorganic acid, and/or iii) by diverting, following anaerobic digestion and separation of the fermented, organic material, the separated liquid organic material fraction comprising one or more sources of nitrogen selected from organic nitrogen sources and inorganic nitrogen sources to the buffer tank
  • An additional pre-treatment processing step in addition to NiX (nitrogen extraction) treatment / lime pressure cooking, which occurs prior to the step of lime pressure cooking, is that of preincubation of the biomass to be lime pressure cooked and later subjected to anaerobic digestion.
  • This additional pre-incubation step also serves to improve biogas production by converting a biomass into smaller constituent parts by chemical hydrolysis, or by biological conversion, using one or more microbial populations and/or one or more enzymes.
  • the initial process of breaking down macromolecular structures of a substrate in an anaerobic fermentation involves a hydrolysis of macromolecular structures, such as proteins, carbohydrates and organic acids.
  • macromolecular structures such as proteins, carbohydrates and organic acids.
  • the constituent parts, or monomers, such as amino acid residues, sugars and fatty acids can be readily metabolized by microbial organisms. Accordingly, hydrolysis of macromolecular components of organic materials represents an initial step in an anaerobic fermentation.
  • Anaerobic fermentations are sensitive to high levels of ammonia as the ammonia inhibits the bacteria which are responsible for the methanogenesis. Hence, when the bacteria are inhibited by high levels of ammonia, reduced amounts of biogas are being produced.
  • the pre-incubation steps of the methods of the present invention are aimed at increasing the removal of nitrogen sources from an organic biomass.
  • the pre-incubation step serves to effectively prevent ammonia inhibition during anaerobic fermentation and biogas production.
  • Nitrogen can be present in an organic biomass either as organic nitrogen - fx nitrogen present in proteins and organic acids - or as inorganic nitrogen - in the form of ammonium.
  • organic bound nitrogen will have to initially be converted into inorganic ammonium, which is then stripped in the form gaseous ammonia. This is performed under suitable conditions - primarily involving a high pH and an increased temperature.
  • the ammonium available for stripping in the lime pressure cooker is determined by the amount of inorganic nitrogen which is entered into the lime pressure cooker for ammonia stripping.
  • a further pre-treatment step in the form of a pre-incubation of an organic biomass is introduced.
  • the pre-incubation step comprises one or both of a pre- fermentation step and/or a chemical hydrolysis and N mineralisation step.
  • Pre-fermentation can result in a hydrolysis and/or further break-down of e.g. proteins, carbohydrates and other macromolecules present in an organic biomass.
  • hydrolysis of macromolecules can also be obtained by microbial means - and not exclusively by chemical means.
  • the pre-incubation step comprises a microbial fermentation resulting in the decomposition of organic macromolecules present in the organic material which is to be subsequently subjected to anaerobic fermentation and biogas fermentation.
  • the microbial fermentation and/or hydrolysis of macromolecules present in an organic material which takes place during the pre-incubation step will thus contribute to an increased N- mineralization process during the pre-incubation step(s).
  • the conversion of organic N to inorganic N which takes place at the pre-incubation step is in one embodiment of the present invention at least facilitated by biological and enzymatic processes catalyzed by microbial organisms present in the biomass comprising the organic bound N.
  • the methods of the present invention can be characterized as a two-step fermentation method in which the individual steps are separated by a thermo-chemical processing step - i.e. lime pressure cooking - performed at an elevated temperature and pressure, and under alkaline pH conditions.
  • the first fermentation step - preceding the thermo-chemical processing step - is a facultative anaerobic fermentation reaction during which, in one embodiment of the present invention, essentially no biogas is produced - as the organic material can be expected to undergo initial fermentation stages during the first fermentation step, but not, or only to a limited extent, methanogenesis.
  • Methanogenesis constitutes one of the latter stages of an anaerobic fermentation - i.e. a stage which is reached only after prior stages, such as e.g. acidogenesis and acetogenesis.
  • the second fermentation step which takes place after the thermo-chemical processing step - is a strictly anaerobic methanogenesis. Accordingly, the second fermentation step is aimed at producing biogas by using the pre-fermented and thermo-chemically treated organic material as a substrate.
  • a dual fermentation method for generating biogas from anaerobic fermentation of processed organic material comprising solid and liquid parts, said method comprising the steps of i) subjecting an organic material comprising one or more sources of nitrogen to a facultative anaerobic fermentation resulting in at least partial hydrolysis of the organic material and at least partial conversion of organic N (nitrogen) present in the organic material to inorganic N, and wherein essentially no biogas is produced; ii) subjecting the organic material fermented in step i) to lime pressure cooking, wherein the lime-pressure cooking results in a further hydrolysis of said organic material, and wherein said lime pressure cooking step results in the conversion of inorganic N to ammonia fluids; iii) subjecting the organic material fermented in step i) and subjected to lime
  • step ii) to a strictly anaerobic fermentation resulting in the production of biogas under conditions wherein the pH level of the anaerobic fermenter is kept within a predetermined pH range by contacting or injecting the organic material with fluids comprising C0 2 in amount sufficient to achieve said pH control.
  • the first microbial fermentation reaction results in a conversion of organic bound N to inorganic N - an increased amount of biogas can be produced in the second microbial fermentation reaction (i.e. the methanogenesis) - as more inorganic N enters the lime pressure cooking step - where the inorganic N is converted to gaseous ammonia which is stripped.
  • the pre-incubation step achieves a convertion of
  • the overall nitrogen removal per kg of substrate added is therefore in this scenario increased from 3.9 g TAN/kg to 1 1.7 g TAN/kg.
  • the pre-incubation thus reduces overall the TAN-concentration in the anaerobic digester (biogas fermenter).
  • the facultative anaerobic bacteria according to the methods of the present invention have a temperature optimum in the range of from approx. 30°C to 37°C. Accordingly, the bacteria can be termed "mesophilic" because of this temperature optimum. It has also been observed that seeding of the pre-incubation is important for the pre- fermentation which takes place - and approx. 10 to 20 % (w/w) of the contents of a pre- fermentation tank is preferably retained and re-circularized to the next batch pre-fermentation. Accordingly, several interconnected pre-fermenters can be present - so that one can seed approx. 10 to 20 % (w/w) of the contents of one pre-fermenter into a connected pre-fermenter.
  • any suitable number such as fx 2, 3, 4, 5 or 6 interconnected pre-fermentation tanks can be operated as individual, but connected pre-fermentation "batch" fermentations at different stages of the pre-fermentation can be present.
  • Each "batch" pre-fermenter is connected to the lime-pressure cooker and pre-fermented biomass can be diverted from any pre-fermenter to the lime pressure cooker. In this way, one will be able to operate the methods of the present invention as a continuous fermentation process for pre-fermentation and biogas production.
  • the maximum TS (total dry matter) content of the biomass subjected to pre-fermentation is preferably approx. 30%, such as at the most 25 % (w/w).
  • the pH optimum for the pre-fermentation is broad and ranges from a pH value of approx. 6.5 to a pH value of approx. 8.5. pH values following a pre-fermentation are preferably in the range of from approx. 6.0 to approx. 7.5.
  • the duration of the pre-fermentation will depend on the reaction conditions, including
  • the pre-fermentation is at the most approx. 96 hours, such as at the most 72 hours, for example at the most 60 hours, such as at the most 50 hours, for example 40 hours. However, both longer and shorter durations can be employed.
  • At least 80%, such as at least 85%, for example at least 90%, such as at least 95% or more of all nitrogen containing organic acids, such as e.g. uric acid, are converted to ammonia N during a pre-fermentation step operated under the conditions disclosed e.g. herein above.
  • a minimum of 30% such as a minimum of 40%, for example a minimum of 50%, such as a minimum of 60% of the organic bound nitrogen originating from protein is converted into inorganic N during a pre-fermentation.
  • the anaerobic fermentation can in principle be conducted either i) as a pre-incubation step, prior to a nitrogen extraction step, and/or ii) in the form of an anaerobic fermentation and biogas production (methanogenesis, cf. above) conducted following a nitrogen extraction step. This is illustrated in figures 26 to 29.
  • Acetate and hydrogen produced in the first stages of an anaerobic fermentation can be used directly by methanogens.
  • Other molecules such as volatile fatty acids (VFAs) with a chain length that is greater than that of acetate, must first be catabolised into compounds that can be directly metabolised by methanogens.
  • VFAs volatile fatty acids
  • the biological process of acidogenesis is one wherein there is further breakdown of the remaining components by acidogenic (fermentative) bacteria.
  • VFAs are created along with ammonia, carbon dioxide, and hydrogen sulphide, as well as other by-products.
  • the third stage of an anaerobic fermentation is acetogenesis.
  • simple molecules created through the acidogenesis phase are further digested by acetogens to produce largely acetic acid as well as carbon dioxide and hydrogen.
  • the final stage of an anaerobic fermentation is that of methanogenesis.
  • Methanogens metabolise intermediate compounds formed during the preceding stages of the anaerobic fermentation, and these compounds are metabolised into methane, carbon dioxide, and water.
  • the afore-mentioned compounds are the major constituents of a biogas.
  • Methanogenesis is sensitive to both high and low pHs - and methanogenesis generally occurs between pH 6.5 and pH 8. Remaining, non-digestible organic material that the microbes present in the biogas fermenter cannot metabolise, along with any dead bacterial remains, constitutes what is termed the digestate from the fermentation.
  • organic materials Apart from having a high energy potential, many organic materials also have a high content of nitrogen (N) - in the form of inorganic N (calculated as TAN - total amount of N (NH 3 and NH 4 + )) and organic N e.g. present in proteins, uric acid and other organic sources of N.
  • N nitrogen
  • TAN total amount of N
  • organic N e.g. present in proteins, uric acid and other organic sources of N.
  • organic N and / or protein will gradually be converted to ammonia e.g. during an anaerobic fermentation resulting in the production of biogas.
  • the formation of ammonia in a bio energy plant - especially at high levels - represents a problem as many biogas producing bacteria are sensitive to high levels of ammonia - and high ammonia levels in a biogas fermenter will thus reduce or inhibit the production of methane.
  • the formation of high levels of ammonia i.e. above a certain threshold level, cf. below, will kill biogas producing bacteria and inhibit any further biogas formation.
  • the inhibitory levels of ammonia in a biogas fermenter depend on the conditions used. Under thermophilic fermentation conditions, approx. 3.0 to 4.2 kg ammonia per ton of biomass is considered inhibitory, while under mesophilic fermentation conditions the figure is approx. 5.0 to 7.0 kg ammonia per ton of biomass - depending of the pH value in the digester.
  • the biogas generating fermentation process can be expected to be completely inhibited at ammonia levels of approx. 7.0 kg to 7.5 kg ammonia per ton of biomass. Accordingly, at this high level of ammonia, fermentation of organic materials by biogas producing bacteria no longer takes place.
  • ammonia (NH 3 ) which is inhibitory to the biogas production.
  • the equilibrium between ammonia and ammonium (NH 4 + ) salts will depend on e.g. pH and temperature. The higher the pH and the higher the temperature, the more the equilibrium is shifted towards the ammonia.
  • Stripping of ammonia will result in a decreased pH value in the fermenter and it is preferred that the pH value of an anaerobic biogas fermentation shall be below a pH value of approx. 8.5.
  • the above-cited ammonia inhibition threshold values are generally taken into consideration when operating commercial biogas plants using conventional organic materials as substrates for the biogas producing bacteria. Many such plants are operated according to a two step strategy initially adopting thermophile digestion conditions in a first fermentation step and mesophile digestion conditions in a separate and subsequent, second fermentation step.
  • the present invention thus also provides a technical solution to the problem of how to improve biogas production in a commercial biogas plant.
  • the solution involves novel and inventive methods for reducing organic N contents in an organic biomass material further comprising at least one carbon (C) source during or after the progress of performing an anaerobic fermentation resulting in the production of biogas.
  • C carbon
  • the anaerobic fermentation resulting in the production of biogas may be preceded by one or more initial processing steps aimed at stripping ammonia N from the organic biomass material prior to the biogas production.
  • One such initial processing step is a pre-incubation step - performed prior to lime pressure cooking - wherein organic N forming part of the biomass to be processed is converted to inorganic N by chemical hydrolysis or by microbial action.
  • the pre-incubation step takes place in a preincubation tank, as illustrated e.g. in Figs. 26 to 29.
  • the pre-incubation step can comprise or be in the form of a facultative, anaerobic fermentation resulting in at least partly converting organic N fractions, including protein N and uric acid N, into an inorganic N fraction which, under suitable conditions, can be stripped as gaseous ammonia by lime pressure cooking, or a processing step functionally equivalent with lime pressure cooking, albeit without subjecting the organic biomass material to a pressure.
  • lime pressure cooking can also be achieved by simply heating the organic biomass material to a temperature of e.g. above 75°C to 80°C for a longer period of time, but in the absence of applying any pressure above 1 bar.
  • one initial processing step is that of lime pressure cooking - a step which subjects the optionally pre-incubated organic biomass material, cf. herein above, to an initial hydrolysis under alkaline conditions at an elevated pressure - i.e. more than 1 bar - and at a temperature of more than 100°C.
  • ambient pressure, or a vacuum can also be used for stripping gaseous ammonia from the optionally pre-incubated organic biomass material. It is thus possible to conduct - as an alternative to lime pressure cooking - a step in which the heating of the optionally pre- incubated, organic biomass material takes place at ambient pressure or under vacuum.
  • yet another pre-treatment step may be used for increasing the conversion of organic bound N in an organic biomass.
  • the lime pressure cooked organic material can be diverted to a buffer tank and the retention time in this buffer tank determines the result of this pre-treatment step.
  • the pH is preferably adjusted to a pH value of less than 8.5, such as less than or about 8.0, for example less than or about 7.5, such as less than or about 7.0, but preferably not less than 6.0.
  • a further conversion and mineralization of organic bound N in an organic biomass can be allowed to occur in the buffer tank and - optionally - ammonia can also be stripped from the buffer tank.
  • Ammonia N stripped from the organic material e.g. under a lime pressure cooking step - and/or during pre-incubation, and/or during buffer tank treatment - can initially be diverted to a stripper and sanitation tank - or alternatively diverted directly to an absorption column for absorption of the stripped ammonia N.
  • the stripper and sanitation tank will also be connected to an absorption column for absorption of the stripped ammonia N.
  • no organic bound N is converted to ammonia during the lime pressure cooking step.
  • organic bound N is converted to ammonia both during the pre-incubation step and during the subsequent anaerobic fermentation resulting in the production of biogas.
  • Ammonia N stripped from the organic material prior to, during, or after the lime pressure cooking step can be diverted to a stripper and sanitation tank for further incubation under conditions resulting in further conversion of organic N to inorganic N - or, alternatively, diverted directly to an absorption column for absorption of the stripped ammonia N.
  • the absorption column can also be connected to the stripper and sanitation tank so that any ammonia N stripped from the stripper tank can be diverted to the absorption column.
  • the lime pressure cooked and, at least partly, ammonia N stripped organic material is
  • the lime pressure cooked organic material is initially diverted to a buffer tank prior to being diverted to the biogas fermenter.
  • Mixing of lime pressure cooked material with further organic materials, for which there is no need for performing a lime pressure cooking step, can take place in a buffer tank prior to diverting the mixture to the biogas fermenter for anaerobic fermentation.
  • anaerobically fermented organic material is separated into a solid and a liquid fraction.
  • the liquid fraction comprising ammonia N is diverted, or re-cycled, to the lime pressure cooker for stripping of ammonia.
  • One principle for large scale stripping of ammonia from e.g. a biomass is to increase the pH in combination with aerating and/or heating of the biomass.
  • Ca(OH) 2 or CaO collectively referred to as lime, can be used to increase the pH in a lime pressure cooking step.
  • Lime is used on an industrial scale by for instance the cement industry and is therefore cheap and readily available as a bulk ware.
  • Other bases may also be employed, such as e.g. NaOH or KOH.
  • stripped ammonia When the stripped ammonia is absorbed and an ammonia concentrate is produced, one can divert stripped ammonia to e.g. sulphuric acid present in an absorption column.
  • Sulphuric acid is an industrial bulk ware and it is available in a technical quality appropriate for use in
  • absorption columns stripping ammonia from slurry and other waste waters (e.g. Sacuk et al. 1994). It is often preferred to strip ammonia by performing a thermal and chemical hydrolysis of a biomass at temperatures of e.g. around or less than 100°C - and at a pressure of about 1 atm. Thermal and chemical hydrolysis of a biomass represents one way to increase the availability of organic material for biogas generation.
  • the present invention concerns methods for performing an anaerobic digestion of a biomass, such as e.g. organic materials comprising one or more of animal manures, energy crops, category 2 waste materials, and similar biomaterials.
  • a biomass such as e.g. organic materials comprising one or more of animal manures, energy crops, category 2 waste materials, and similar biomaterials.
  • biomasses capable of being used as an "input biomass” and subsequently processed in accordance with the methods of the present invention are disclosed herein below in more detail.
  • the biomasses can comprise e.g. solid manure waste products from e.g. animal farms, poultry farms, dairies, slaughterhouses, marine fish farms, fish and meat industries as wells as energy crops and or other plants.
  • the input biomass or feedstock can also comprise liquid manure, dry litter, such as cattle, poultry, offal from cattle, poultry, mink, vegetable oil and glycerin, sludge, whey and the like, corn silage, fish category 2 waste, and industrial waste, including category 3 waste materials.
  • Biomass can also be any material that comes from plants. Some plants, like sugar cane and sugar beets, store the energy as simple sugars. These are mostly used for food. Other plants store the energy as more complex sugars, called starches. These plants include grains like corn and are also used for food.
  • cellulosic biomass Another type of plant matter, called cellulosic biomass, is made up of very complex sugar polymers, and is not generally used as a food source. This type of biomass is under consideration as a feedstock for bioethanol production. Specific feed stocks under
  • Cellulose is the most common form of carbon in biomass, accounting for 40%-60% by weight of the biomass, depending on the biomass source. It is a complex sugar polymer, or polysaccharide, made from the six-carbon sugar, glucose. Its crystalline structure makes it resistant to hydrolysis, the chemical reaction that releases simple, fermentable sugars from a polysaccharide.
  • Hemicellulose is also a major source of carbon in biomass, at levels of between 20% and 40% by weight. It is a complex polysaccharide made from a variety of five- and six-carbon sugars. It is relatively easy to hydrolyze into simple sugars but the sugars are difficult to ferment to ethanol.
  • Lignin is a complex polymer, which provides structural integrity in plants. It makes up 10% to 24% by weight of biomass. It remains as residual material after the sugars in the biomass have been converted to ethanol. It contains a lot of energy and can be burned to produce steam and electricity for the biomass-to-ethanol process.
  • the percentages cited herein below are weight percentages - i.e. (weight / weight), or (mass / mass).
  • the input biomass has in one aspect of the present invention a carbon content of from 5% to 90% by weight, such as from 5% to 10%, for example from 10% to 15%, such as from 15% to 20%, for example from 20% to 25%, such as from 25% to 30%, for example from 30% to 35%, such as from 35% to 40%, for example from 40% to 45%, such as from 45% to 50%, for example from 50% to 55%, such as from 55% to 60%, for example from 60% to 65%, such as from 65% to 70%, for example from 70% to 75%, such as from 75% to 80%, for example from 80% to 85%, such as from 85% to 90% or any combination of these intervals.
  • 5% to 90% by weight such as from 5% to 10%, for example from 10% to 15%, such as from 15% to 20%, for example from 20% to 25%, such as from 25% to 30%, for example from 30% to 35%, such as from 35% to 40%, for example from 40% to 45%, such as from 45% to 50%, for example from 50% to 55%, such as from 55%
  • the input biomass has in one aspect of the present invention a protein content of from 5% to 90% by weight, such as from 5% to 10%, for example from 10% to 15%, such as from 15% to 20%, for example from 20% to 25%, such as from 25% to 30%, for example from 30% to 35%, such as from 35% to 40%, for example from 40% to 45%, such as from 45% to 50%, for example from 50% to 55%, such as from 55% to 60%, for example from 60% to 65%, such as from 65% to 70%, for example from 70% to 75%, such as from 75% to 80%, for example from 80% to 85%, such as from 85% to 90% or any combination of these intervals.
  • 5% to 90% by weight such as from 5% to 10%, for example from 10% to 15%, such as from 15% to 20%, for example from 20% to 25%, such as from 25% to 30%, for example from 30% to 35%, such as from 35% to 40%, for example from 40% to 45%, such as from 45% to 50%, for example from 50% to 55%, such as from 55%
  • the input biomass has in one aspect of the present invention a fat or lipid content of from 5% to 90% by weight, such as from 5% to 10%, for example from 10% to 15%, such as from 15% to 20%, for example from 20% to 25%, such as from 25% to 30%, for example from 30% to 35%, such as from 35% to 40%, for example from 40% to 45%, such as from 45% to 50%, for example from 50% to 55%, such as from 55% to 60%, for example from 60% to 65%, such as from 65% to 70%, for example from 70% to 75%, such as from 75% to 80%, for example from 80% to 85%, such as from 85% to 90% or any combination of these intervals.
  • 5% to 90% by weight such as from 5% to 10%, for example from 10% to 15%, such as from 15% to 20%, for example from 20% to 25%, such as from 25% to 30%, for example from 30% to 35%, such as from 35% to 40%, for example from 40% to 45%, such as from 45% to 50%, for example from 50% to 55%, such as
  • the input biomass has in one aspect of the present invention a nitrogen or ammonia content of from 5% to 90% by weight, such as from 5% to 10%, for example from 10% to 15%, such as from 15% to 20%, for example from 20% to 25%, such as from 25% to 30%, for example from 30% to 35%, such as from 35% to 40%, for example from 40% to 45%, such as from 45% to 50%, for example from 50% to 55%, such as from 55% to 60%, for example from 60% to 65%, such as from 65% to 70%, for example from 70% to 75%, such as from 75% to 80%, for example from 80% to 85%, such as from 85% to 90% or any combination of these intervals.
  • the input biomass has in one aspect of the present invention a fiber content of from 5% to 90% by weight, such as from 5% to 10%, for example from 10% to 15%, such as from 15% to 20%, for example from 20% to 25%, such as from 25% to 30%, for example from 30% to 35%, such as from 35% to 40%, for example from 40% to 45%
  • 90% by weight such as from 5% to 10%, for example from 10% to 15%, such as from 15% to 20%, for example from 20% to 25%, such as from 25% to 30%, for example from 30% to 35%, such as from 35% to 40%, for example from 40% to 45%, such as from 45% to 50%, for example from 50% to 55%, such as from 55% to 60%, for example from 60% to 65%, such as from 65% to 70%, for example from 70% to 75%, such as from 75% to 80%, for example from 80% to 85%, such as from 85% to 90% or any combination of these intervals.
  • the input biomass has in one aspect of the present invention a sugar content of from 5% to 90% by weight, such as from 5% to 10%, for example from 10% to 15%, such as from 15% to 20%, for example from 20% to 25%, such as from 25% to 30%, for example from 30% to 35%, such as from 35% to 40%, for example from 40% to 45%, such as from 45% to 50%, for example from 50% to 55%, such as from 55% to 60%, for example from 60% to 65%, such as from 65% to 70%, for example from 70% to 75%, such as from 75% to 80%, for example from 80% to 85%, such as from 85% to 90% or any combination of these intervals.
  • 5% to 90% by weight such as from 5% to 10%, for example from 10% to 15%, such as from 15% to 20%, for example from 20% to 25%, such as from 25% to 30%, for example from 30% to 35%, such as from 35% to 40%, for example from 40% to 45%, such as from 45% to 50%, for example from 50% to 55%, such as from 55%
  • the input biomass has in one aspect of the present invention a polysaccharide content of from 5% to 90% by weight, such as from 5% to 10%, for example from 10% to 15%, such as from 15% to 20%, for example from 20% to 25%, such as from 25% to 30%, for example from 30% to 35%, such as from 35% to 40%, for example from 40% to 45%, such as from 45% to 50%, for example from 50% to 55%, such as from 55% to 60%, for example from 60% to 65%, such as from 65% to 70%, for example from 70% to 75%, such as from 75% to 80%, for example from 80% to 85%, such as from 85% to 90% or any combination of these intervals.
  • a polysaccharide content of from 5% to 90% by weight, such as from 5% to 10%, for example from 10% to 15%, such as from 15% to 20%, for example from 20% to 25%, such as from 25% to 30%, for example from 30% to 35%, such as from 35% to 40%, for example from 40% to 45%, such as from 45% to
  • the input biomass has in one aspect of the present invention a monosaccharide content of from 5% to 90% by weight, such as from 5% to 10%, for example from 10% to 15%, such as from 15% to 20%, for example from 20% to 25%, such as from 25% to 30%, for example from 30% to 35%, such as from 35% to 40%, for example from 40% to 45%, such as from 45% to 50%, for example from 50% to 55%, such as from 55% to 60%, for example from 60% to 65%, such as from 65% to 70%, for example from 70% to 75%, such as from 75% to 80%, for example from 80% to 85%, such as from 85% to 90% or any combination of these intervals.
  • a monosaccharide content of from 5% to 90% by weight, such as from 5% to 10%, for example from 10% to 15%, such as from 15% to 20%, for example from 20% to 25%, such as from 25% to 30%, for example from 30% to 35%, such as from 35% to 40%, for example from 40% to 45%, such as from 45% to
  • the input biomass has in one aspect of the present invention a lignin content of from 5% to 90% by weight, such as from 5% to 10%, for example from 10% to 15%, such as from 15% to 20%, for example from 20% to 25%, such as from 25% to 30%, for example from 30% to 35%, such as from 35% to 40%, for example from 40% to 45%, such as from 45% to 50%, for example from 50% to 55%, such as from 55% to 60%, for example from 60% to 65%, such as from 65% to 70%, for example from 70% to 75%, such as from 75% to 80%, for example from 80% to 85%, such as from 85% to 90% or any combination of these intervals.
  • a lignin content of from 5% to 90% by weight, such as from 5% to 10%, for example from 10% to 15%, such as from 15% to 20%, for example from 20% to 25%, such as from 25% to 30%, for example from 30% to 35%, such as from 35% to 40%, for example from 40% to 45%, such as from 45% to 50%,
  • the input biomass has in one aspect of the present invention a hemicellulose content of from 5% to 90% by weight, such as from 5% to 10%, for example from 10% to 15%, such as from 15% to 20%, for example from 20% to 25%, such as from 25% to 30%, for example from 30% to 35%, such as from 35% to 40%, for example from 40% to 45%, such as from 45% to 50%, for example from 50% to 55%, such as from 55% to 60%, for example from 60% to 65%, such as from 65% to 70%, for example from 70% to 75%, such as from 75% to 80%, for example from 80% to 85%, such as from 85% to 90% or any combination of these intervals.
  • a hemicellulose content of from 5% to 90% by weight, such as from 5% to 10%, for example from 10% to 15%, such as from 15% to 20%, for example from 20% to 25%, such as from 25% to 30%, for example from 30% to 35%, such as from 35% to 40%, for example from 40% to 45%, such as from 45% to 50%,
  • the input biomass has in one aspect of the present invention a starch content of from 5% to 90% by weight, such as from 5% to 10%, for example from 10% to 15%, such as from 15% to 20%, for example from 20% to 25%, such as from 25% to 30%, for example from 30% to 35%, such as from 35% to 40%, for example from 40% to 45%, such as from 45% to 50%, for example from 50% to 55%, such as from 55% to 60%, for example from 60% to 65%, such as from 65% to 70%, for example from 70% to 75%, such as from 75% to 80%, for example from 80% to 85%, such as from 85% to 90% or any combination of these intervals.
  • a starch content of from 5% to 90% by weight, such as from 5% to 10%, for example from 10% to 15%, such as from 15% to 20%, for example from 20% to 25%, such as from 25% to 30%, for example from 30% to 35%, such as from 35% to 40%, for example from 40% to 45%, such as from 45% to 50%, for example from 50%
  • the input biomass has in one aspect of the present invention a sugar polymer content of from 5% to 90% by weight, such as from 5% to 10%, for example from 10% to 15%, such as from 15% to 20%, for example from 20% to 25%, such as from 25% to 30%, for example from 30% to 35%, such as from 35% to 40%, for example from 40% to 45%, such as from 45% to 50%, for example from 50% to 55%, such as from 55% to 60%, for example from 60% to 65%, such as from 65% to 70%, for example from 70% to 75%, such as from 75% to 80%, for example from 80% to 85%, such as from 85% to 90% or any combination of these intervals.
  • 5% to 90% by weight such as from 5% to 10%, for example from 10% to 15%, such as from 15% to 20%, for example from 20% to 25%, such as from 25% to 30%, for example from 30% to 35%, such as from 35% to 40%, for example from 40% to 45%, such as from 45% to 50%, for example from 50% to 55%, such as from
  • the input biomass has in one aspect of the present invention a cellulose content of from 5% to 90% by weight, such as from 5% to 10%, for example from 10% to 15%, such as from 15% to 20%, for example from 20% to 25%, such as from 25% to 30%, for example from 30% to 35%, such as from 35% to 40%, for example from 40% to 45%, such as from 45% to 50%, for example from 50% to 55%, such as from 55% to 60%, for example from 60% to 65%, such as from 65% to 70%, for example from 70% to 75%, such as from 75% to 80%, for example from 80% to 85%, such as from 85% to 90% or any combination of these intervals.
  • a cellulose content of from 5% to 90% by weight, such as from 5% to 10%, for example from 10% to 15%, such as from 15% to 20%, for example from 20% to 25%, such as from 25% to 30%, for example from 30% to 35%, such as from 35% to 40%, for example from 40% to 45%, such as from 45% to 50%, for example from 50%
  • the input biomass has in one aspect of the present invention a pH between 0 and 14, such as from 0 to 1 , for example from 1 to 2, such as from 2 to 3, for example from 3 to 4, such as from 4 to 5, for example from 5 to 6, such as from 6 to 7, for example from 7 to 8, such as from 8 to 9, for example from 9 to 10, such as from 10 to 11 , for example from 11 to 12, such as from 12 to 13, for example from 13 to 14, or any combination of these intervals.
  • the methods of the present invention are capable of producing increased amounts of renewable energy while at the same time refining several nutrients comprised in the digested biomass to fertilizers of commercial quality.
  • ammonia stripping results in lowering of the ammonia concentration by more than 10%, such by more than 20%, such as by more than 30%, such as by more than 40%, such as by more than 50%, such as by more than 60%, such as by more than 70%, such as by more than 80%, such as by more than 90%, such as by more than 95% or such as more than 99%.
  • the level of ammonia and/or nitrogen can be measured before and after the ammonia stripping step and the lowering of the ammonia concentration can be determined.
  • the ammonia stripping can result in an ammonium concentration of less than 50 g dm “3 , such as less than 40 g dm “3 , such as less than 30 g dm “3 , such as less than 20 g dm “3 , such as less than 15 g dm “3 , such as less than 10 g dm “3 , such as less than 8 g dm “3 , such as less than 6 g dm “3 , such as less than 2 g dm “3 , such as less than 1 g dm "3 , such as less than 0.5 g dm "3 ,or such as less than 0.1 g dm “3 .
  • Anaerobic digestion as used herein shall denote any breakdown of organic matter by bacteria in the absence of oxygen.
  • the terms anaerobic digestion and anaerobic fermentation are used interchangeably herein.
  • a method for generating biogas from an anaerobic fermentation of processed organic material comprising solid and liquid parts, said method comprising the steps of i) subjecting a first organic material comprising one or more organic material sources of organic and inorganic nitrogen to a facultative anaerobic fermentation and converting at least partly said one or more sources of organic nitrogen into inorganic nitrogen, ii) diverting the anaerobically fermented first organic material comprising one or more sources of nitrogen to a lime pressure cooker; iii) subjecting said first organic material to a lime pressure cooking step resulting in at least partly hydrolysing said first organic material comprising one or more sources of nitrogen, wherein said lime pressure cooking step results in the formation of ammonia fluids; iv) diverting said ammonia fluids formed in the lime pressure cooker to an
  • the above cited method may comprise the further steps of xi) diverting said organic materials from said one or more fermenters to a
  • the above cited method may comprise the step of diverting the liquid fraction comprising one or more sources of nitrogen to the lime pressure cooker and/or to the buffer tank. Accordingly, there is also provided the further steps of xiii) diverting said liquid fraction comprising one or more sources of nitrogen to the lime pressure cooker and/or to the buffer tank, and either xiv) mixing, in the lime pressure cooker and/ or in the buffer tank, said liquid fraction comprising one or more sources of nitrogen with a first organic material and/or a further organic material comprising one or more sources of nitrogen wherein, when the mixing takes place in the lime pressure cooker, ammonia originating from said one or more sources of nitrogen present in said liquid fraction can be stripped from said liquid fraction together with ammonia originating from additional inorganic nitrogen sources present in the first or further organic material, and/or, wherein, when the mixing takes place in the buffer tank, the pH of the organic material present in the buffer tank will be lowered as a result of the addition of the liquid fraction to the buffer tank.
  • the pH value of the anaerobically fermented and lime pressure cooked organic material can be lowered by preferably contacting the anaerobically fermented and lime pressure cooked organic material with an acid, such as an organic or inorganic acid, or by contacting the pre-incubated and lime pressure cooked organic material with a carbon dioxide (C0 2 ) containing gas.
  • an acid such as an organic or inorganic acid
  • the diversion to the buffer tank of C0 2 containing gas, or an organic or inorganic acid controls the pH of the organic material diverted to the buffer tank.
  • a pH value of from 7.0 to 8.2 is also preferred in the anaerobic digester in which the strictly anaerobic fermentation resulting in the production of biogas is conducted under conditions wherein the pH level is kept within this predetermined pH range.
  • the one or more sources of nitrogen present in the organic material of the liquid fraction preferably comprise inorganic nitrogen sources, such as ammonium salts.
  • Solid organic material is preferably diverted to the lime pressure cooker from a reception station suitable for receiving solid organic material
  • liquid organic material is preferably diverted to the lime pressure cooker from a reception tank suitable for receiving liquid organic material.
  • Lime is preferably diverted to the lime pressure cooker from a lime storage tank suitable for diverting lime directly to the lime pressure cooker.
  • Solid and/or liquid organic materials for which there is no need for lime pressure cooking can be diverted directly to the buffer tank and mixed with lime pressure cooked organic material in the buffer tank. It is possible in one embodiment to divert ammonia fluids from the buffer tank to the absorption unit, prior to diverting said mixed organic materials stripped of ammonia from the buffer tank to one or more fermenters suitable for the production of biogas.
  • the mixed organic materials are preferably fermented initially in a first fermenter under a first set of fermentation conditions, and subsequently diverted to a second or further fermenter and fermented under a second or further set of fermentation conditions.
  • the organic materials are initially fermented under thermophile fermentation conditions and subsequently, in a separate fermentation step, the organic materials are fermented under mesophilic fermentation conditions.
  • the biogas produced by thermophilic and/or mesophilic fermentation is preferably diverted to a gas storage facility operably connected to the one or more fermenters.
  • Biogas as used herein denotes a renewable, gaseous fuel derived from biological materials that can be used as an energy source instead of fossil fuels, typically to replace conventional natural gas, propane, heating fuel oil, diesel fuel, or gasoline.
  • Raw biogas is composed of a mixture of combustible gases (principally methane, but also including hydrogen and light hydrocarbons, such as e.g. carbon monoxide, ethane, etc.), and various inert gases and impurities, such as carbon dioxide and hydrogen sulfide.
  • Methane is a combustible gas with the chemical formula CH 4 that can come from fossil or renewable processes.
  • the present invention can be used for producing increased amounts of biogas from a wide range of organic substrates, including all types of animal manures, energy crops, crops residues and other organic waste materials, including category 2 waste materials.
  • the present invention is also directed to an optimized waste-to-energy process based on bio- gasification using anaerobic digestion and wet fermentation for increasing the yield of energy obtained e.g. per ton of biomass.
  • the above-cited method can include a subsequent slurry separation step, i.e. one or more steps resulting in the refinement of selected nutrients, such as phosphor (P) and/or potassium (K) contained in e.g. animal manures.
  • the invention may be applied to separate the main nutrients nitrogen (N) and/or phosphorus (P) from animal manures and refine the nutrients to fertilizer products of commercial quality.
  • the organic material to be pre-incubated and/or lime pressure cooked can comprise a maximum of 50% solid parts, such as a maximum of 40% solid parts, for example a maximum of 30% solid parts, such as a maximum of 20% solid parts.
  • the organic material may be in the form of a liquid fraction comprising a maximum of 10% solid parts, or the organic material to be pre-incubated or lime pressure cooked may be mixed with such a liquid fraction.
  • the lime pressure cooking of the organic material can be performed at a temperature of from more than 100°C to preferably less than 250°C, at a pressure of from preferably 2 to preferably less than 20 bar, and with an addition of lime sufficient to reach a pH value of from about 9 to preferably less than 12, and with an operation time of from at least 10 minutes to preferably less than 60 minutes.
  • the method may include the step of adding lime (CaO) in an amount of from about 2 to preferably less than 80 g per kg dry matter organic material, such as from about 5 to preferably less than 60 g per kg dry matter.
  • lime CaO
  • the methods of the present invention may comprise the step of diverting an organic material to a first fermenter, under a first set of fermentation conditions, and subsequently diverting said fermented, organic material to a second, or further, fermenter, and fermenting said organic material under a second, or further, set of fermentation conditions.
  • the conditions can be thermophile fermentation conditions and/or mesophile fermentation conditions.
  • the method may include performing the one or more biogas fermentation step(s) at a temperature of from about 15°C to preferably less than about 65°C, such as at a temperature of from about 25°C to preferably less than about 55°C, for example at a temperature of from about 35°C to preferably less than about 45°C.
  • the fermentation may be allowed to occur over a time of from about 5 days to preferably less than 15 days.
  • the biogas production is achieved by bacterial anaerobic fermentation of the organic material, and the fermentation method may initially performing the biogas production in the first of two plants by anaerobic bacterial fermentation of the organic material, initially by fermentation with thermophilic bacteria in the first plant, followed by diverting the thermophilicly fermented organic material to a second plant, wherein a fermentation with mesophilic bacteria can take place.
  • Thermophilic reaction conditions include a reaction temperature ranging from 40°C to 75°C, such as a reaction temperature ranging from 55°C to 60°C, whereas a reaction temperature ranging from 20°C to 40°C, such as from 30°C to 35°C is characteristic for a mesophilic fermentation.
  • the methods of the present invention results in a biogas production output in Nm 3 per 1 ,000 tons biomass input of more than 70,000 Nm 3 , such as more than 80,000 Nm 3 per 1 ,000 tons input, for example more than 90,000 Nm 3 per 1 ,000 tons input, such as more than 100,000 Nm 3 per 1 ,000 tons input, for example more than 1 10,000 Nm 3 per 1 ,000 tons input, such as more than 120,000 Nm 3 per 1 ,000 tons input, for example more than 130,000 Nm 3 per 1 ,000 tons input, such as more than 140,000 Nm 3 per 1 ,000 tons input, for example more than 150,000 Nm 3 per 1 ,000 tons input, such as more than 160,000 Nm 3 per 1 ,000 tons input, for example more than 170,000 Nm 3 per 1 ,000 tons input, such as more than 180,000 Nm 3 per 1 ,000 tons input, for example more than 190,000 Nm 3 per 1 ,000 tons input, for example more than 200,000 Nm 3
  • methods of the present invention results in an electricity output in KWh per 1 ,000 tons biomass input of more than 200, such as more than 220 KWh per 1 ,000 tons input, for example more than 240 KWh per 1 ,000 tons input, such as more than 260 KWh per 1 ,000 tons input, for example more than 280 KWh per 1 ,000 tons input, such as more than 300 KWh per 1 ,000 tons input, for example more than 320 KWh per 1 ,000 tons input, such as more than 340 KWh per 1 ,000 tons input, for example more than 360 KWh per 1 ,000 tons input, such as more than 380 KWh per 1 ,000 tons input, for example more than 400 KWh per 1 ,000 tons input, such as more than 450 KWh per 1 ,000 tons input, for example more than 500 KWh per 1 ,000 tons input, such as more than 600 KWh per 1 ,000 tons input, for example more than 700 KWh
  • methods of the present invention results in a heat output in MWh per 1 ,000 tons biomass input of more than 200 MWh per 1 ,000 tons input, such as more than 220 MWh per 1 ,000 tons input, for example more than 240 MWh per 1 ,000 tons input, such as more than 260 MWh per 1 ,000 tons input, for example more than 280 MWh per 1 ,000 tons input, such as more than 300 MWh per 1 ,000 tons input, for example more than 320 MWh per 1 ,000 tons input, such as more than 340 MWh per 1 ,000 tons input, for example more than 360 MWh per 1 ,000 tons input, such as more than 380 MWh per 1 ,000 tons input, for example more than 400 MWh per 1 ,000 tons input, such as more than 450 MWh per 1 ,000 tons input, for example more than 500 MWh per 1 ,000 tons input, such as more than 600 MWh per 1
  • methods of the present invention results in a steam output in MWh per 1 ,000 tons biomass input of more than 40 MWh per 1 ,000 tons input, such as more than 50 MWh per 1 ,000 tons input, for example more than 60 MWh per 1 ,000 tons input, such as more than 70 MWh per 1 ,000 tons input, for example more than 80 MWh per 1 ,000 tons input, such as more than 90 MWh per 1 ,000 tons input, for example more than 100 MWh per 1 ,000 tons input, such as more than 105 MWh per 1 ,000 tons input, for example more than 1 10 MWh per 1 ,000 tons input, such as more than 115 MWh per 1 ,000 tons input, for example more than 120 MWh per 1 ,000 tons input, such as more than 125 MWh per 1 ,000 tons input, for example more than 130 MWh per 1 ,000 tons input, such as more than 150 MWh per 1 ,000 tons input
  • a plant for generating biogas from an anaerobic fermentation of processed organic material comprising solid and liquid parts, said plant comprising i) a lime pressure cooker for hydrolysing a first organic material comprising one or more sources of nitrogen; ii) an absorption unit for absorbing and condensing ammonia fluids diverted to the absorption unit from the lime pressure cooker when said first organic material is subjected to lime pressure cooking; iii) a buffer tank for mixing lime pressure cooked organic material with a further organic material prior to diverting the mixed, organic materials to one or more fermenters; wherein the buffer tank is optionally fitted with means for diverting a C0 2 containing gas to the organic material present in the buffer tank; iv) one or more fermenters for anaerobically fermenting said organic materials diverted to said one or more fermenters from said buffer tank, wherein said fermentation results in the generation of biogas, wherein the one or more fermenters for anaerobically fermenting said organic materials diverted to said one
  • the lime pressure cooker for hydrolysing said first organic material comprising one or more sources of nitrogen is preferably operably connected to a reception station suitable for receiving solid organic material and/or to a reception tank suitable for receiving liquid organic material.
  • the lime pressure cooker is also in one embodiment operably connected to a lime storage tank suitable for diverting lime directly to the lime pressure cooker.
  • the absorption unit for absorbing and condensing ammonia fluids diverted to the absorption unit from the lime pressure cooker preferably comprises a steam condenser and a scrubber.
  • the buffer tank is operably connected to a reception station suitable for receiving solid organic material and/or operably connected to a reception tank suitable for receiving liquid organic material. Also, the buffer tank is in one embodiment further operably connected to the absorption unit for absorbing and condensing ammonia fluids, wherein said connection allows ammonia to be stripped in the buffer tank and diverted to the absorption unit.
  • the plant according to the second aspect of the invention in one embodiment further comprises a silage tank for storage of energy crops.
  • the plant comprises one, or more than one, fermenter for anaerobically fermenting said organic materials, wherein said one or more than one fermenter are serially connected so that organic material having been fermented in a first fermenter under a first set of fermentation conditions can be diverted to a second or further fermenter and fermented under a second or further set of fermentation conditions.
  • the plant according to the present invention does not contain a stripper and sanitation tank connected to the lime pressure cooker and an absorption unit for absorbing ammonia N. Accordingly, the lime pressure cooker is connected directly to the absorption unit and ammonia formed in the lime pressure cooker during operation thereof under practical circumstances is diverted directly to the absorption unit.
  • the lime pressure cooker is also connected to a buffer tank which is connected to the lime pressure cooker and which is not connected to the absorption unit. The buffer tank receives lime pressure cooked biomass from the lime pressure cooker and optionally also biomass which has not been processed in the lime pressure cooker.
  • the buffer tank is connected to one or more biogas reactors.
  • the lime pressure cooker is connected to the one or more biogas reactors and receives from said one or more biogas reactors a liquid fraction comprising ammonia N.
  • the liquid fraction is obtained by removing digestate from liquid biomass removed from the one or more biogas reactors. This can be achieved in a number of ways according to state-of-the-art methods.
  • the obtained liquid fraction can be diverted or recycled back to the lime pressure cooker where the liquid fraction is stripped for ammonia N without mixing the liquid fraction with a further biomass.
  • the liquid fraction is mixed with a further biomass which enters the lime pressure cooker prior to processing and stripping of ammonia N. Once stripped at least partly for ammonia N, the liquid fraction can be diverted to the buffer tank and mixed with biomass entering this buffer tank directly and without having been subjected to an initial lime pressure cooking step.
  • stripping of ammonia N from the liquid fraction takes place only by lime pressure cooking and not by any other means.
  • the more than one fermenter comprises at least one primary fermenter suitable for thermophilic fermentation and at least one secondary fermenter suitable for mesophilic fermentation.
  • a gas storage facility is operably connected to the one or more than one fermenters.
  • the bioenergy plant according to the present invention further comprises biogas fermenters comprising one or more service facilities, or maintenance shafts.
  • the plant may further comprise a lime pressure cooker for hydrolysing said first organic material comprising one or more sources of nitrogen is operably connected to a reception tank suitable for receiving liquid organic material.
  • the plant may further comprise a lime pressure cooker for hydrolysing said first organic material comprising one or more sources of nitrogen is operably connected to a lime storage tank suitable for diverting lime directly to the lime pressure cooker.
  • the plant may further comprise an absorption unit for absorbing and condensing ammonia fluids diverted to the absorption unit from the lime pressure cooker comprises a steam condenser and a scrubber.
  • the plant may further comprise a pre-incubation tank is operably connected to a reception station suitable for receiving solid organic material, wherein the buffer tank is also operably connected to a reception tank suitable for receiving liquid organic material.
  • the pre-incubation tank can further be operably connected to the absorption unit for absorbing and condensing ammonia fluids, wherein said connection allows ammonia to be stripped in the pre-incubation tank and diverted to the absorption unit.
  • the plant may further comprise more than one fermenter for anaerobically fermenting said organic materials, wherein said more than one fermenters are serially connected so that organic material having been fermented in a first fermenter under a first set of fermentation conditions can be diverted to a second or further fermenter and fermented under a second or further set of fermentation conditions.
  • the more than one fermenter preferably comprises at least one primary fermenter suitable for thermophilic fermentation and, serially connected thereto, at least one secondary fermenter suitable for mesophilic fermentation.
  • the plant may further comprise a gas storage facility operably connected to the afore-mentioned, one or more biogas fermenters.
  • a method for generating biogas from an anaerobic fermentation of processed organic material comprising solid and liquid parts, said method comprising the steps of i) diverting a first organic material comprising one or more sources of nitrogen to a pre-incubation tank and subjecting said organic material to a mineralisation by chemical and/or biological means, wherein the mineralisation results in the conversion of organic N (nitrogen) present in the organic material to inorganic N; ii) diverting the pre-incubated first organic material to a lime pressure cooker and subjecting said first pre-incubated organic material to lime pressure cooking, wherein said lime pressure cooking step results in the formation of ammonia fluids; iii) diverting pre-incubated and lime pressure cooked organic material from said lime pressure cooker to a buffer tank and lowering the pH value of the pre- incubated and lime pressure cooked material by contacting the pre-incubated and lime pressure cooked organic material with a carbon dioxide (C0 2 ) containing gas.
  • a carbon dioxide C0 2
  • the method of item 1 comprising the further step of diverting said ammonia fluids formed in the lime pressure cooker to an absorption unit, and absorbing and condensing the ammonia fluids diverted to the absorption unit from the lime pressure cooker.
  • the method of item 1 comprising the further step of mixing in the buffer tank the lime pressure cooked organic material with a further organic material; wherein the further organic material preferably has not been subjected to lime pressure cooking prior to the mixing with the lime pressure cooked organic material.
  • any of items 1 to 3 comprising the further step of diverting the optionally mixed, organic material(s) from the buffer tank to at least one, anaerobic biogas fermenter suitable for conducting an anaerobic, bacterial digestion of the organic material, wherein the anaerobic, bacterial digestion results in the generation of biogas.
  • the method of item 4 comprising the further step of fermenting, under anaerobic fermentation conditions, the organic material diverted to the anaerobic biogas fermenter, and collecting the biogas resulting from said anaerobic fermentation of said organic material.
  • the method of item 5 comprising the further step of diverting part or all of the organic material from the anaerobic biogas fermenter to a separation unit, and separating the organic material into a solid organic material fraction and a liquid organic material fraction comprising one or more sources of nitrogen selected from organic nitrogen sources and inorganic nitrogen sources.
  • the method of item 6 comprising the further step of diverting said liquid organic material fraction comprising one or more sources of nitrogen to the pre-incubation tank and/or to the lime pressure cooker.
  • the method of item 7 comprising the further step of mixing, in the pre-incubation tank and/or in the lime pressure cooker, said liquid fraction comprising one or more sources of nitrogen with a second organic material comprising one or more sources of nitrogen selected from organic nitrogen sources and inorganic nitrogen sources.
  • the method of item 8 comprising the further step of mineralising the mixture of second organic material and liquid fraction by chemical and/or biological means, when the liquid fraction comprising one or more sources of nitrogen is diverted to the pre-incubation tank and mixed with the second organic material in the pre-incubation tank, wherein the mineralisation results in a conversion of organic N (nitrogen) present in the second organic material to inorganic N.
  • any of items 8 and 9 comprising the further step of stripping ammonia from the mixture of second organic material and liquid fraction, when the liquid fraction comprising one or more sources of nitrogen is diverted to the lime pressure cooker and mixed with the second organic material in the lime pressure cooker.
  • a method for generating biogas from an anaerobic fermentation of processed organic material comprising solid and liquid parts comprising the steps of i) diverting a first organic material comprising one or more sources of nitrogen to a pre-incubation tank and subjecting said organic material to a mineralisation by chemical and/or biological means, wherein the mineralisation results in the conversion of organic N (nitrogen) present in the organic material to inorganic N; ii) diverting the pre-incubated first organic material to a lime pressure cooker and subjecting said first pre-incubated organic material to lime pressure cooking, wherein said lime pressure cooking step results in the formation of ammonia fluids; iii) diverting pre-incubated and lime pressure cooked organic material from said lime pressure cooker to a buffer tank and lowering the pH value of the pre- incubated and lime pressure cooked material in the buffer tank.
  • the method of item 1 1 comprising the further step of diverting said ammonia fluids formed in the lime pressure cooker to an absorption unit, and absorbing and condensing the ammonia fluids diverted to the absorption unit from the lime pressure cooker.
  • the method of item 1 1 comprising the further step of mixing in the buffer tank the lime pressure cooked organic material with a further organic material; wherein the further organic material preferably has not been subjected to lime pressure cooking prior to the mixing with the lime pressure cooked organic material.
  • any of items 11 to 13 comprising the further step of diverting the optionally mixed, organic material(s) from the buffer tank to at least one, anaerobic biogas fermenter suitable for conducting an anaerobic, bacterial digestion of the organic material, wherein the anaerobic, bacterial digestion results in the generation of biogas.
  • the method of item 14 comprising the further step of fermenting, under anaerobic fermentation conditions, the organic material diverted to the anaerobic biogas fermenter, and collecting the biogas resulting from said anaerobic fermentation of said organic material.
  • any of items 1 to 10 and 15 wherein the pH value of the organic material diverted to the anaerobic biogas fermenter is maintained within a predetermined pH-range by contacting the organic material present in the anaerobic biogas fermenter with recirculated biogas or a biogas diverted to the anaerobic biogas fermenter from an external source, wherein said contacting results in said pH value being maintained within a predetermined pH-range.
  • any of items 14 to 16 comprising the further step of diverting part or all of the organic material from the anaerobic biogas fermenter to a separation unit, and separating the organic material into a solid organic material fraction and a liquid organic material fraction comprising one or more sources of nitrogen selected from organic nitrogen sources and inorganic nitrogen sources.
  • the method of item 17 comprising the further step of diverting said liquid organic material fraction comprising one or more sources of nitrogen to the pre-incubation tank and/or to the lime pressure cooker.
  • the method of item 18 comprising the further step of mixing, in the pre-incubation tank and/or in the lime pressure cooker, said liquid fraction comprising one or more sources of nitrogen with a second organic material comprising one or more sources of nitrogen selected from organic nitrogen sources and inorganic nitrogen sources.
  • the method of item 19 comprising the further step of mineralising the mixture of second organic material and liquid fraction by chemical and/or biological means, when the liquid fraction comprising one or more sources of nitrogen is diverted to the pre-incubation tank and mixed with the second organic material in the pre-incubation tank, wherein the mineralisation results in a conversion of organic N (nitrogen) present in the second organic material to inorganic N.
  • the method of any of items 19 and 20 comprising the further step of stripping ammonia from the mixture of second organic material and liquid fraction, when the liquid fraction comprising one or more sources of nitrogen is diverted to the lime pressure cooker and mixed with the second organic material in the lime pressure cooker.
  • the method of any of items 4 and 14 comprising the further step of diverting to the anaerobic digester a further organic biomass, wherein said further organic biomass is mixed in the anaerobic digester with the optionally mixed, organic material(s) diverted to the anaerobic digester from the buffer tank.
  • the method of item 28, wherein the lowering of the pH value of the lime pressure cooked organic material present in the buffer tank is obtained i) by contacting said organic material in the buffer tank with a C0 2 containing gas, such as biogas, and/or ii) by contacting said organic material in the buffer tank with an acid selected from an organic acid and an inorganic acid, and/or iii) by diverting, following anaerobic digestion and separation of the fermented, organic material, the separated liquid organic material fraction comprising one or more sources of nitrogen selected from organic nitrogen sources and inorganic nitrogen sources to the buffer tank
  • the rate of conversion of organic N to inorganic N in the pre-incubation tank is proportional to the amount of water present in the pre-incubation tank.
  • the method of any of items 1 to 30, wherein, for oxygen levels greater than normal oxygen levels in the pre-incubation tank, the rate of conversion of the organic N into inorganic N in the pre-incubation tank is inversely proportional to oxygen level.
  • the method of any of items 1 to 30, wherein, for oxygen levels equal to or lower than the normal oxygen levels in the pre-incubation tank, the rate of conversion of the organic N to inorganic N in the pre-incubation tank is substantially same.
  • the rate of conversion of the organic N to inorganic N in the pre-incubation tank is directly proportional to the amount of seeding organic material used, wherein the seeding organic material used involves adding material from an active fraction in an amount of approximately 10% to 30% w/w of the active fraction, preferably 10% to 25% w/w, more preferably around 10% to 20% w/w, wherein the active fraction comprises a separate pre-incubated organic material.
  • the seeding is selected from adding material by retaining the amount of the active fraction of a first pre-fermentation for subsequent pre- fermentation in the pre-incubation tank; and/ or adding material by receiving, in a first preincubation tank, the amount of the active fraction from a second pre-incubation tank.
  • any of items 1 to 30, wherein the process in the pre-incubation tank comprises an anaerobic facultative microbial fermentation carried out by microbial organisms present in the organic material and optionally also in the seeding material diverted to the pre-incubation tank.
  • maximum of 40% solid parts such as a maximum of 30% solid parts for example a maximum of 25% solid parts such as a maximum of 20% solid parts.
  • any of the items 1 to 30, wherein the amount of added CaO used for lime pressure cooking is from about 2 to about 80 g per kg dry matter, such as from about 5 to about 60 g per kg dry matter.
  • the method of any of the items 1 to 30, wherein the lime pressure cooking of the organic material is performed at a temperature of from about 100°C to preferably less than 250°C, under a pressure of from 2 to preferably less than 20 bar, with addition of lime sufficient to reach a pH value of from about 9 to preferably less than 12, and with an operation time of from at least one 10 minutes to preferably about less than 60 minutes.
  • any of items 1 to 30, wherein said mixed organic materials are fermented in a first, anaerobic fermenter under a first set of fermentation conditions, and subsequently diverted to a second, or further, anaerobic fermenter and fermented under a second or further set of fermentation conditions.
  • the method of any of the items 1 to 30, wherein said organic materials are fermented under thermophile fermentation conditions and/or mesophile fermentation conditions.
  • the method of any of the items 1 to 30, wherein said organic materials are initially fermented under thermophile fermentation conditions and subsequently under mesophile fermentation conditions.
  • thermophile and/or mesophile fermentation conditions are diverted to a gas storage facility operably connected to the one or more fermenters.
  • the thermophilic reaction conditions include a reaction temperature ranging from 40°C to 65°C.
  • the thermophilic reaction conditions include a reaction temperature ranging from 45°C to 60°C.
  • the mesophilic reaction conditions include a reaction temperature ranging from 20°C to 40°C.
  • the method of any of item 57, wherein the mesophilic reaction conditions include a reaction temperature ranging from 32°C to 38°C.
  • the method of any of the items 58 and 59, wherein the thermophilic reaction is performed for about 5 to15 days, such as for about 7 to 10 days.
  • removed inorganic nitrogen with respect to the total nitrogen of the organic material is at least 65%.
  • anaerobic biogas fermenter with a third organic material for initiating the fermentation of the organic material diverted to the anaerobic fermenter.
  • said method comprising the steps of a pre-incubation step comprising receiving in a pre-incubation tank an organic material having a first part removable inorganic N and organic N, and increasing the amount of the removable inorganic N by converting the organic N into a second part of the removable inorganic N using first fermentation conditions, wherein the pre-incubation step is free or at least substantially free from a generation of biogas; a nitrogen stripping step comprising stripping the removable inorganic N, comprising the first part and the second part, from the pre-incubated organic material using a lime-pressure cooker for stripping said removable inorganic N; and a second fermentation step comprising anaerobically fermenting, in an anaerobic biogas fermenter, the pre-incubated organic material that is mixed with a further organic material for the generation of biogas wherein the organic material is contacted with a C0 2 containing gas either following the lime-pressure cooking step and prior to the anaerobic fermentation step, or during the an
  • the pre-incubation tank is operably connected to a lime pressure cooker; wherein the mineralisation results in the conversion of organic N (nitrogen) present in the organic material to inorganic N; ii) a lime pressure cooker for further mineralisation of a first organic material
  • a buffer tank for mixing lime pressure cooked organic material with a further organic material prior to diverting the mixed, organic materials to one or more fermenters, said buffer tank being operably connected to a gas storage facility suitable for storage of C0 2 containing gas, such as biogas; v) a gas storage facility suitable for storage of C0 2 containing gas, such as biogas, wherein the gas storage facility is operably connected to the buffer tank; vi) one or more fermenters for anaerobically fermenting said organic materials diverted to said one or more fermenters from said buffer tank, wherein said fermentation results in the generation of biogas.
  • the plant according to item 67 wherein the plant further comprises vii) a separation unit for separating organic materials diverted to the separation unit from said one or more fermenters, wherein said separation of said organic materials results in the generation of a solid organic material fraction and a liquid fraction comprising one or more sources of nitrogen; and viii) means for diverting said liquid fraction comprising one or more sources of nitrogen to the lime pressure cooker, wherein said liquid fraction is mixed in the lime pressure cooker with first organic material comprising one or more sources of nitrogen.
  • the buffer tank is further operably connected to the absorption unit for absorbing and condensing ammonia fluids, wherein said connection allows ammonia to be stripped in the buffer tank and diverted to the absorption unit.
  • Nitrogen present in an organic material such as e.g. layer manure, such as chicken litter, can be divided into different fractions which may be determined individually either by analysis or by calculation.
  • the total amount of nitrogen is made up of inorganic nitrogen (TAN) and organic nitrogen (OrgN).
  • the TAN fraction is made up of ammonia (NH 3 ) and ammonium (NH 4 + ).
  • inorganic nitrogen containing compounds such as nitrate (N0 3 " ), are usually present in such small amounts that they are considered insignificant.
  • the OrgN fraction is made up of two sub-fractions: Protein bound nitrogen and uric acid bound nitrogen.
  • TKN can be determined by the Kjeldahl procedure (ISO 5663/DIN EN 25 663)
  • TAN can be determined by titration (ISO 5663/DIN EN 25 663)
  • Uric acid nitrogen can be determined by HPLC (Pekic et al.; Chromatographia; Vol. 27; No. 9/10; May 1989)
  • the pH of the treated material is raised using burnt lime (CaO). This facilitates a reduction in the TAN pool by removal of ammonia and this is a necessary step in order to obtain high removal efficiencies (see Equation 3 and Equation 4).
  • a disadvantage to this method is the low solubility of CaO (S) , which results in substantial amounts of residual CaO (S) after the NiX treatment.
  • the surplus base will subsequently be dissolved in the anaerobic digester leading to undesirably high pH levels.
  • ammonia is the toxic part of the TAN pool, the residual base in the digester counteracts the benefits of the TAN removal obtained during NiX treatment.
  • the experimental setup consisted of
  • a flow meter for measuring and controlling gas flow.
  • NiX treated material Gas from the pressurised cylinder was bubbled through the NiX treated material via the connective tubing. The flow was controlled and monitored using the reduction valve and the flow meter. The NiX treated material was continously mixed and the pH measured at regular intervals.
  • Table 1 shows the details of the netralisation set-up parameters.
  • Fig. 25 illustrates the pH development during the experiment referred to in Table 1 above.
  • the pH of NiX treated material was successivefully lowered from 8.5 to 7.75 using C0 2(g) .
  • This value was chosen to ensure a suitably low pH value in the biogas reactor while disturbing the buffer systems of the NiX material as little as possible.
  • other experiments have shown that it is possible to lower the pH to at least 7.2, which is significantly lower than the pH of the original material prior to base addition and NiX treatment (pH 7.7).
  • pure C0 2( g ) may be substituted with biogas ( ⁇ 40% C0 2( g ) ), although with longer neutralisation times.
  • Example 2 The below graph illustrates the requirement for TAN removal (%) - in order to maintain the level of gaseous ammonia in the anaerobic digester below 700 mg per litre - as a function of the pH value of the fermented biomaterial.
  • the value of 700 mg NH 3 per litre is defining a threshold value for NH 3 inhibition and it is thus desirable not to exceed this value.
  • Two different scenarios are represented in the below illustration. In Scenario 1 , the contents of total ammonia N (TAN) in the fermenter is 15,000 mg per litre, whereas in Scenario 2, an amount of total ammonia N (TAN) of 20,000 mg per litre is present in the fermenter.
  • the final methane yield for untreated hen litter reached 293 NmL CH 4 /g VS. 90% of this value was obtained after 11 days anaerobic digestion.
  • the expected methane yield, when digesting the treated and untreated hen litter in a two-stage CSTR setup, may be seen in Figure 26.
  • the calculation combines the digestion speeds and final methane yields obtained in batch to predict the methane production in a two-stage thermophilic/mesophilic system with a 15 days retention time in each reactor. In this setup approx. 91 % of the batch BMP value may be realised. Also, there is no effect of NiX treatment on methane yield in CSTR. 1 Materials and Methods
  • Total solids (TS) and volatile solids (VS) contents of the hen litter were determined in triplicate prior to BMP analysis. TS were determined by heating the samples to 105°C for a minimum of 24 hours. VS were determined by burning the samples at 550°C for 3 - 4 hours.
  • Substrate age (at time of sampling) ⁇ 1 day
  • TAN Total Ammonium Nitrogen
  • TKN Total Kjeldahl Nitrogen
  • the Nix technology consists of a thermochemical treatment of the substrate.
  • Substrate was mixed with burnt lime (CaO) and water to a final concentration of 1.5 wt% burnt lime and 30% TS, prior to subjecting the mixture to elevated temperatures and pressure.
  • the treatment was performed in a pilot scale pressure cooker in which saturated water steam was used to raise the pressure to 4 barg and the temperature to 146 °C. After treatment pressure was released over a period of 20-30 minutes. Samples were collected and processed according to the flowchart below.
  • the BMP assay was carried out according to the German VDI4630 protocol for analysis of methane potentials in agricultural biomasses with minor modifications.
  • the batches were prepared in 500 ml glass bottles.
  • the inoculum was taken from the thermophilic main digester of Foulum biogas plant and incubated at 52 ⁇ 1 °C for 10-14 days before substrate addition in order to minimize the relative contribution from the inoculum to the total gas production. 200 ml of inoculum was used per bottle.
  • the BMP assay was carried out at two different concentrations of substrate.
  • Each batch bottle was prepared by addition of either 0.9 or 1.7 g VS followed by addition of 200 ml inoculum.
  • Resulting substrate VS concentration in each of the substrate batch bottles was 4.5 and 8.5 g substrate VS/L inoculum respectively.
  • 3 replicates were incubated.
  • 6 bottles of 1.0 g cellulose per 200 ml inoculum were incubated (positive controls).
  • For determination of the contribution from the inoculum to the CH 4 production 6 control bottles of 200 ml inoculum were also incubated (blanks).
  • After addition of inoculum and substrate all bottles were flushed with N 2 and closed with gas tight rubber stoppers and aluminium screw lids before incubation at 52 ⁇ 1 °C in a heat cabinet for the duration of the batch test.
  • the CH 4 content in the headspace of the batch bottles was measured by GC (Shimadzu 2010) equipped with a capillary column (wax 0.53 mm ID, 30 m) and a FID detector.
  • the specific methane yield (Nml methane per gram substrate VS added) is calculated by subtraction of background, normalizing to standard pressure and temperature (STP) and relating the yield to the quantity of VS added.
  • TAN total ammonium nitrogen
  • TKN total nitrogen
  • Table 6 shows the content of TAN and TKN in the substrate.
  • Organic nitrogen (OrgN) is calculated by subtraction of TAN from TKN.
  • the methane production curves from the two different substrate concentrations showed no significant difference, meaning that there is no observable inhibition at the concentrations used in this assay.
  • the data points from the two concentrations are averaged and used as one.
  • Specific methane yield B(t) is shown in Figure 28 for both untreated hen litter and NiX treated hen litter.
  • Empirical data are shown as points and the best-fit curve from non-linear analysis of the empirical data are shown as lines. For details of the best-fit curve with calculated kinetic constants, please refer to Table 7, below.
  • the curve for the untreated hen litter shows a steady increase in methane production until a maximum yield of 293 ( ⁇ 9) Nml CH 4 /g VS is obtained after about 30-40 days.
  • the curve for the NiX treated hen litter is almost identical to the untreated, and shows a steady increase in methane production until a maximum yield of 292 ( ⁇ 6) Nml CH 4 /g VS is obtained.
  • TAN ammonium-N
  • TAN is the sum of ammonium (NH 4 +) and free ammonia (NH 3 ), the latter of which has been identified as the inhibiting agent.
  • the NH 3 -fraction of TAN is positively correlated with process temperature and pH.
  • the actual threshold value for ammonia inhibition cannot be universally defined as microbial adaptation and potential neutralizing effect of other ions can be in play.
  • Most studies indicate however, that the concentration of free ammonia should be kept below 1 ,000 mg/L in the digester. Some studies even suggest that the level for significant inhibition is to be found as low as 600 mg/L.
  • chicken litter can be diluted with water to reduce both dry matter and N to acceptable levels for the AD process.
  • This approach results in extra costs for water consumption and process heat and more importantly in excess production of effluent, which can be fatal to the economic feasibility of a project.
  • Recirculation of digester effluent possibly after removal of suspended solids can potentially be a solution to reducing water and heat consumption as well as effluent production, but nitrogen content in the effluent stream will be at the same level or higher than in the digester.
  • Controlling the N-balance in the digester is thus the key to a stable AD process based on chicken litter as mono-substrate with recirculation of separated digester liquid. Water addition can be necessary for maintaining the water balance.
  • the investigation was carried out in a pilot scale plant during the period from November 2011 to July 2013.
  • the test was based on a single step digestion at 37°C with hydraulic retention times as specified below for each of the phases.
  • test period is therefore divided into three phases as follows:
  • Phase 3 As phase 2 but with addition of post-treatment of NiX treated mixture in order to control pH
  • KPI key performance indicators
  • VFA Volatile Fatty Acids
  • Methane yield (Figure 29) was stable around 300 L CH 4 /kg VS for more than the first 4 weeks of the period but a decrease began in mid-December and continued until early January where a new stable yield level slightly above 200 L CH 4 /kg VS was reached. This was followed by unstable peaks of higher yields leading to a sudden drop to less than 200 L CH 4 /kg VS at the end of the period.
  • NH 3 showed little variation around a mean value of 900 mg/L during the first 4 weeks but peaked at 1 , 100 mg/L during the following TAN increase which coincided with a pH increase from 8.1 to 8.2 ( Figure 31).
  • NH 3 dropped consecutively to a level of 700-800 mg/L due to a pH decrease from 8.2 to 8.0. This was followed by an increase in pH from around 8.0 to more than 8.1 causing the NH 3 to return to the previous peak value at nearly 1 , 100 mg/L.
  • VFA's were not measured during the first 4 weeks of the period.
  • the first analysis in the second half of December showed a total level of 2,300 mg/L and a healthy profile with acetic acid as the dominating species and with propionic acid as the only other VFA present at a significant concentration ( Figure 32 and Figure 33).
  • the following 3 measurements showed drastic increases in acetic as well as propionic acid to levels of 12,000 and 6,000 mg/L, respectively.
  • the longer-chained VFA also increased from levels close to zero to several hundred mg/L.
  • the TS content in the digester (Figure 34) increased gradually from 10 % during 8 weeks to a plateau around 12.5 % in the first half of January and stayed at this level during the rest the period.
  • the TS content in the recycled liquid showed the same development from an initial level at 5 % to more than 8 %.
  • the loading was reduced by 64 % by a reduction of the daily input without any changes in the composition of the input.
  • 25 % of the digester content was replaced by water on February 27 in an attempt to save the process.
  • Methane yield (Figure 35) immediately started to go up from less than 200 L CH 4 /kg VS and peaked within a few days at +260 L CH 4 /kg VS followed by a very rapid drop during a week to less than 100 L CH 4 /kg VS. This level continued for three weeks after which the gas yield increased dramatically to +560 L CH 4 /kg VS during the last 3 weeks of the period.
  • the concentration of TAN (Figure 36) increased gradually from just below 6,900 mg/L to 7,300 mg/L within the first 3 weeks followed by a drop to 5,600 mg/L at the end of February due to dilution of the digester content with water. This level was maintained for another 2 weeks followed by a slight increase to approx. 5,800 mg/L for the rest of the period.
  • NH 3 decreased from 900 to 800 mg/L during the initial increase in TAN due to falling pH from 8.1 to an estimated 8.0 (Figure 37).
  • Water dilution reduced NH 3 to 600 mg/L followed by a further drop to 400 mg/L caused by a continued drop in pH to less than 7.8.
  • NH3 then rose gradually to 700 mg/L during the rest of the period caused by the pH returning to a level above 8.0.
  • VFA levels were quite constant during the first 2 weeks of the period, but for propionic acid at a much higher level than at the end of the previous period (10,000 vs. 6,000 mg/L).
  • Propionic acid stayed at a level around 10,000 mg/L during the entire period with fluctuations (+/- 2,000 mg/L) but no clear tendency.
  • Acetic acid on the other hand started increasing at the end of February and peaked at a level of more than 25,000 mg/L in mid-March followed by a rapid decrease during the next 2 weeks to 10,000 mg/L.
  • Butyric acid increased constantly during the entire period from less than 200 mg/L reaching a final level of more than 3,000 mg/L (although with fluctuating values from 2,300 to 3, 100 mg/L during the last week). Iso-butyric acid remained relatively constant around 900 +/- 200 mg/L. Valeric acid dropped after water dilution from an initial level around 350 mg/L to below the detection limit and then stabilized at a level around 200 mg/L. Iso-valeric acid gradually increased from 1 ,700 to 2,000 mg/L during the first week and stayed there until the water dilution 10 days later.
  • the concentration then dropped first to a level corresponding to the degree of dilution (1 :3) and then further to 1 ,200 mg/L before increasing gradually to 1 ,900 mg/L followed by a drop to a final level of 1 ,700 mg/L.
  • the TS content in the digester ( Figure 40) had increased since the end of Period 1a to a level of more than 13 %. Water dilution reduced this level 10.7 % but TS continued to increase slowly during the rest of the period ultimately reaching 11.4 %.
  • Methane yield (Figure 41) immediately began to drop from the peak level of more than 560 L CH 4 /kg VS at the end of Period 1 B to around 300 L CH 4 /kg VS three weeks later and finally stabilizing at 250 L CH 4 /kg VS after 6 weeks.
  • composition of the VFA pool ( Figure 44) changed markedly during the period with acetic acid continuing the drop that had started in the last part of Period 1 B. Acetic acid levels had thus dropped to 4,000 mg/L at the start of the period and continued to drop to a final 1 ,500 mg/L.
  • Propionic acid on the other hand, increased in concentration from 9,000 mg/L to peak values above 20,000 mg/L before dropping again to 11 ,000 mg/L at the end of the period.
  • Butyric acid had dropped from a level of more than 3,000 mg/L at the end of the previous to less than 100 mg/L at the first analysis after little more than a week and stayed at this low level during the entire period.
  • Iso-butyric acid maintained the level from the previous period around 900 - 1 ,000 mg/L for the first 3 weeks after which the level dropped to less than 300 mg/L within a week. After a further drop to around 150 mg/L the level increased to around 350 mg/L at the end of the period.
  • Valeric acid fluctuated between 0 and 200 mg/L during the entire period with a tendency towards values in the high end during the last week of the period.
  • Iso-valeric acid dropped from an initial 1 ,600 mg/L to around 600 mg/L during the first three weeks followed by a gradual increase to 1 ,700 mg/L at the end of the period.
  • TS content in the digester had decreased since the end of Period 1 b to 10.3 %. TS increased gradually during the entire period reaching a final level of 1 1.7 %.
  • TS in the recycled liquid remained at around 7.0 % during the first 4 weeks where after a gradual increase to 7.5 % within 2 weeks was observed.
  • Methane yield (Figure 47) was quite constant during the entire period around a mean of 270 L CH 4 /kg VS but with drops to 230-240 L CH 4 /kg VS several times. However, at the end of the period the yield showed an increasing tendency towards a yield level around 300 L CH 4 /kg VS.
  • the initial concentration of TAN ( Figure 48) at 5,200 mg/L increased during the first 2 weeks to a final level of 5,600 mg/L.
  • VFA pool ( Figure 50) stabilised during the period with acetic acid levels around 1 ,500 +/- 200 mg/L.
  • Propionic acid varied between 1 1 ,000 and 19,000 mg/L with no clear trend and with most values at 15,000 +/- 2,500 mg/L.
  • Butyric and valeric acid levels were constant at ⁇ 100 and ⁇ 200 mg/L, respectively, while iso- butyric and iso-valeric acid were constant at 300-400 mg/L and 1 ,300-1 ,8000 mg/L, respectively ( Figure 51).
  • TS in the digester remained in a range from 12.0 to 12.4 % during the entire period.
  • TS in the recycled liquid remained in a range from 7.7 to 8.0 % during the entire period.
  • ammonia is a product of TAN and pH, it is possible to decrease the ammonia levels by decreasing either TAN or pH levels.
  • the TAN pool constitutes -25% of the total nitrogen pool. The rest is organically bound, but the majority of this is mineralised during digestion and released as TAN in the reactor.
  • a novel concept was thus developed to shift the nitrogen pool from organically bound to inorganic prior to the digester, thus allowing for it to be removed in the NiX treatment.
  • nitrogen mineralisation (or simply mineralisation) method developed made it possible to increase the strippable nitrogen fraction more than 5 fold by mineralisation of a large part of the organic nitrogen into TAN.
  • nitrogen mineralisation comprises incubation of the chicken litter with an appropriate mixture of liquid from separated digestate with a microbially active culture at 36°C.
  • the active culture stems from a previous mineralisation, and contains a viable and active microbial culture, which facilitates conversion of up to 75 % of the nitrogen contained in organic compounds into TAN within 24 hours.
  • Nitrogen mineralisation allows for a more efficient stripping process since the amount of nitrogen available per unit chicken litter is much higher.
  • the increased TAN removal potential also necessitates addition of more lime during NiX treatment, which may potentially counteract the lowered TAN levels by increasing digester pH and hence the free ammonia.
  • the assumption in the following phase was that the buffer capacity of the digester is strong enough to maintain pH levels at 8.1 to 8.2.
  • a method was developed to decrease the pH and reduce the residual lime after NiX treatment.
  • the method developed referred to as "pH neutralisation", makes it possible to adjust the pH of the influent material to pH ⁇ 7 (compared to pH 8.5 to 9.0 without pH neutralisation).
  • the effect of the method is to neutralize the base effect of the added lime using the biogas produced by the AD process.
  • TAN levels increase at a slower rate than in Phase 2 (see Figure 53). Steady state has not yet been reached but it appears that the equilibrium will be ⁇ 4500 mg/L. Ammonia levels are also increasing at a significantly slower rate and are presently relatively stable at -500 mg/L. Since TAN levels are close to reaching equilibrium, the major contributor to the ammonia level is pH.
  • pH is not yet stable although there is weak indication that it may stabilise between 8.0 and 8.1. If TAN levels settle at 4500 mg/L and pH at 8.1 , ammonia levels will stay just below 600 mg/L which is generally considered to be the limit below which no ammonia inhibition can be observed.
  • the specific methane production is calculated as the average methane production in the last 7 days relative to the average amount of VS added over the same period. All volumes are reported at STP condition - standard temperature and pressure (273 K and 1 bar). Expected methane production is calculated from a batch BMP test taking into account the retention time in the digester.
  • the methane production is relatively stable with an average of 267 ( ⁇ 3) NL/kg VS over the last 14 days.
  • the predicted methane production is 243 ( ⁇ 18) NL/kg VS.
  • the observed methane production is thus 10% higher than expected. This may be explained by adaptation of the bacterial community to the specific substrate. In batch BMP assays the inoculum is taken from a digester which is not necessarily accustomed to the substrate being tested.
  • the methane production seemed to stabilise close to 300 NL/kg VS.
  • the substrate used contained large amounts of wood shavings which had a tendency to clog the pipes in the digester. It is likely that the shavings in the outlet pipe functioned as a sieve filtering the VS material and artificially increasing the retention time and hence the degradation in the digester.
  • the large drop in methane production in the beginning of June is a result of technical difficulties due to the buildup of wood shavings in the pipes.
  • the digester material was cleaned for excessive shavings and the clots in the pipes removed. In the material used now the shavings are much smaller and make up a significantly less proportion.
  • the amount of total solids (Figure 59) in the digester is still increasing but shows a tendency to stabilise around 11 % TS.
  • the peak at the beginning of June is due to the previously mentioned technical problems with the wood shavings in the biomass.
  • the predicted TS level is between 10.5% and 11 % depending on the extent of degradation in the digester.
  • TAN removal was not maintained at an average 65 % during the entire phase. This target level was achieved during longer periods but for reasons of optimisation of the NiX method where also energy and water consumption is critical sub- optimal TAN-removal was obtained during parts of the phase.
  • Dry matter content in the recycled liquid could not be kept at the target level of 3 % but increased to at or slightly above a constant level of 8 %.
  • the issue of dry matter content in the recycled liquid is of importance not only for the water balance but also for the not well- understood potential negative effects on the AD process of a high suspended solids level in the digester.
  • methane yields at the end of the period were stable and high.
  • the example summarizes experiments performed on broiler litter.
  • the broiler litter is used in a continuous pilot plant biogas trial during which it undergoes a number of treatments including nitrogen mineralisation, NiX treatment and pH adjustment prior to anaerobic digestion for production of biogas.
  • the analyses reported here investigates the effect on biomethane potential (BMP) from each of the different treatments.
  • Broiler litter which has been subjected to nitrogen mineralisation, NiX treatment, and pH- adjustment.
  • the BMP analyses were carried out in two separate setups. In the first setup the effect of mineralisation and NiX treatment at 4 barg was investigated. In the second setup the investigation included mineralisation, NiX treatment at 0 barg and pH adjustment. In the following the samples which are repeated in both setups are averaged.
  • Broiler litter was obtained from a chicken farmer in Northern Ireland, and transported to the Xergi research center, where it was homogenised and stored. After each treatment samples were collected and analysed.
  • NiX treated NiX treated NiX treated NiX treated (4 barg) (0 barg) (0 barg, pH adjusted)
  • NiX treatment at 4 barg shows a small drop in BMP and an increase in digestion speed.
  • the net effect is practically zero and the apparent effects are likely due to small measuring deviations in the beginning of the analysis period.
  • NiX treatment at 0 barg shows no deviations compared to the untreated sample. pH adjusted material shows an increase in both digestion speed and ultimate yield.
  • the expected methane yield, when digesting the untreated and treated samples in a two-stage CSTR setup, may be seen in Figure 61.
  • the calculation combines the digestion speeds and final methane yields obtained in batch with the setup of the CSTR system to predict the methane production.
  • Substrate description Litter from broilers. 0.8 tons of straw/1 .7 tons of
  • the Nix technology consists of a thermochemical treatment of the substrate.
  • Substrate was mixed with burnt lime (CaO) and water to a final concentration of 1.5 wt% burnt lime and 30 % TS, prior to subjecting the mixture to elevated temperatures and pressure.
  • the treatment was performed in a pilot scale pressure cooker in which saturated water steam was used to raise the temperature and/or pressure to 4 barg (corresponding to 146°C) or 0 barg (corresponding to 100 °C). After treatment pressure was released over a period of 20-30 minutes. Samples were collected and processed according to the flowchart below.
  • Example 3 The process giving an overview of the treatment is shown in Example 3, where (chicken litter + CaO + H20) is pressure cooked for sampling and then homogenized for BMP analysis.
  • BMP Bio Methane Potential Test 1.3.1.
  • BMP assay The BMP assay was carried out according to the German VDI4630 protocol for analysis of methane potentials in agricultural biomasses with minor modifications. The batches were prepared in 500 ml infusion glass bottles. The inoculum was taken from the thermophilic, main digester of Foulum biogas plant and incubated at 52 ⁇ 1 °C for 10-14 days before substrate addition in order to minimize the relative contribution from the inoculum to the total gas production. 200 ml of inoculum were used per bottle.
  • the BMP assay was carried out at two different concentrations of deep litter.
  • Each batch bottle was prepared by addition of either 1 or 2 g VS followed by addition of 200 ml inoculum.
  • Resulting substrate VS concentration in each of the substrate batch bottles was 5 and 10 g substrate VS/L inoculum respectively. For each of two different substrate concentrations 3 replicates were incubated.
  • the CH 4 content in the headspace of the batch bottles was measured by GC (Shimadzu 2010) equipped with a capillary column (wax 0.53 mm ID, 30 m) and a FID detector.
  • TS and VS contents of the untreated broiler litter were determined prior to NiX treatment and BMP analysis.
  • the broiler litter was analysed for total ammonium nitrogen (TAN) and total nitrogen (TKN) in the untreated and treated samples.
  • Table 12 shows the content of TAN and TKN in the substrate.
  • Organic nitrogen (OrgN) is calculated by subtraction of TAN from TKN.
  • the specific methane yield (ml_ methane per gram substrate VS added) is calculated by subtraction of background and normalizing according to VS concentration.
  • the broiler litter was analysed for biomethane potential and compared to litter subjected to a combination of nitrogen mineralisation, NiX treatment, and pH adjustment.
  • the BMP analyses were carried out in two separate setups. In the first setup the effect of mineralisation and NiX treatment at 4 barg was investigated.
  • a layer manure biomass material can have a total dry matter content (i.e. total solid content (TS)) of about 58% to about 66% (w/w), typically approx. 62% (w/w) and a content of volatile solids (VS) of about 50% (w/w) to about 58% (w/w), typically approx. 54% (w/w).
  • TS total solid content
  • VS content of volatile solids
  • Table 17 illustrates the distribution of TAN (Total Ammonia N), uric acid N and protein N in a typical layer manure biomass i) prior to pre-treatment in accordance with the methods of the present
  • thermo-chemical lime-pressure treatment i.e. thermo-chemical lime-pressure treatment
  • NiX nitrogen extraction
  • TAN Analysis and determination of TAN can be performed essentially in accordance with the Kjeldahl analysis (Total-N) set out in ISO 5663 / DIN EN 25 663.
  • an untreated layer manure biomass may typically contain about 34 g organic N/kg TS - with an about equal distribution of the organic N pool between uric acid N and protein N.
  • the inorganic N pool typically amounts to less than about 15 g N/kg TS - depending on the specific biomass and the applied storage time and conditions.
  • the TAN contents are stated as 11.3 g N/kg TS.
  • the availability of strippable TAN is increased from about 1 1.3 g N/kg TS to more than 3 times this amount - 36.7 g N/kg TS.
  • thermo-chemical lime pressure cooking step is essentially unable to mineralize organic N, including protein N.
  • TAN strippable, inorganic N
  • TKN value of about 21.3 g N/kg TS for (NiX) thermo-chemical lime pressure cooked layer manure biomass.
  • protein N remains unchanged following the (NiX) thermo-chemical lime pressure cooking step.

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Abstract

La présente invention concerne le domaine du traitement de la biomasse et de la production de bioénergie et facilite un traitement efficace de la biomasse et une production accrue d'énergie renouvelable à partir du traitement et de la fermentation anaérobie d'une large variété de matières organiques. Afin de réguler la valeur du pH de la biomasse au cours de son traitement, un gaz contenant du CO2, tel que, p.ex., le biogaz ou le gaz de carneau, est ajouté à la biomasse présente dans le réservoir tampon et/ou dans le digesteur anaérobie relié de manière fonctionnelle au réservoir tampon.
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