All patent and non-patent references cited in the present application are incorporated herein by reference in their entirety.

Technical Field of the Invention

The present invention is directed to anaerobic fermentation of a nitrogen rich biomass, such as a poultry litter biomass, and to the production of bioenergy. The invention aims to re-use liquid biomass fractions, and to optimize energy consumption used for biomass processing with the objective of increasing biogas production when fermenting e.g. a poultry litter biomass.

Background of the Invention

Traditional energy sources are finite and there are considerable concerns over the extent of remaining reserves. A continued utilization of fossil fuels as a dominant energy source is not consistent with the long-term sustainability of the environment.

Renewable energy sources are a promising alternative to many traditional fossil and other non-renewable energy sources. Biomass materials represent one source of renewable energy, but biomass materials must be processed efficiently to generate affordable, clean and efficient energy forms. An optimization of biomass processing is required to ensure an efficient exploitation of biomass energy.

The energy potential associated with a fermentable biomass can be difficult to exploit, and there is a need for more efficient methods for processing fermentable biomasses without using excessive energy and natural resources, including water, in order to secure an increased exploitation of the energy potential of the biomass.

More efficient biomass processing thus results in an increased production of renewable energy sources, such as e.g. biogas. One of the challenges associated with biomass energy extraction is the optimization of the energy yield. While a biomass may be perceived to contain an energy reservoir, this energy reservoir often cannot readily be released in a convenient form. Accordingly, one challenge in the technical field of the present invention is to extract as much energy as possible from the biomass, by using as little energy as possible, in order to increase the total energy yield of the process.

Another challenge is to minimize the "back-end" disposal of both solids and liquids generated as a result e.g. of the choice of biomaterial(s), liquids employed for biomass suspension or dilution, and the processing and fermentation conditions employed for conducting an anaerobic biogas fermentation.

Accordingly, "front-end" addition of excessive amounts of liquids for biomass suspension or dilution prior to biogas fermentation will generate the "back-end" problem of how to dispose of such added liquids.

Addition of liquids for biomass suspension or dilution will thus generally increase the cost of operating an anaerobic fermenter, and a practical balance and economic optimization will thus have to be found in order to optimize "front-end" additions and "back-end" disposals.

Anaerobic fermentations are sensitive to high levels of ammonia as ammonia inhibits the microorganisms responsible for performing the methanogenesis, and when methanogenic microorganisms are inhibited by high levels of ammonia during anaerobic biogas fermentation, reduced amounts of biogas are being produced.

In order to prevent ammonia inhibition, or in order to reduce the problem of ammonia inhibition during anaerobic fermentation of a biomass comprising poultry manure, it is necessary to remove significant parts of the inorganic nitrogen pool present in a biomass prior to or during anaerobic fermentation of the biomass.

Accordingly, it is often necessary to remove, e.g. during a continuous anaerobic biogas fermentation, significant parts of the inorganic nitrogen "pool" which is being generated e.g. during anaerobic biogas fermentation of a poultry manure containing biomass. Summary of the Invention

The present invention facilitates an efficient fractionation and processing of a poultry manure comprising biomass. The present invention also enables an increased

production of renewable energy, such as biogas, from a continuous, anaerobic liquid state fermentation of a poultry manure comprising biomass.

A fractionation of a fermented poultry manure comprising biomass into solid and liquid fermentation medium fractions, and subsequent processing and re-cycling of the liquid fermentation medium fraction, ensures an optimal utilization of the energy potential associated with each of said solid and liquid fermentation medium fractions.

Many types of 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 generation of biogas. This process represents a conversion of an energy potential to a readily usable energy source.

Biogas fermentation of a poultry litter containing biomass will need to take into account the gradual initial conversion over time of organic bound ammonia N sources into inorganic sources of ammonia N, and the subsequent conversion of these inorganic ammonia N sources in a poultry litter containing biomass into ammonia fluids during a continuous, liquid state anaerobic biogas fermentation. In particular, there is a need for improving both the conversion of organic nitrogen sources into inorganic nitrogen sources as well as the removal of the inorganic nitrogen sources during continuous, liquid state anaerobic biogas fermentation processes in which e.g. poultry manures, and optionally also other organic materials having high organic bound N contents, are used for biogas production. The present invention solves this need.

Nitrogen can be present in a biomass, such as a poultry manure containing biomass, either as organic nitrogen - such as organic nitrogen present in proteins and organic acids, including uric acid - or as inorganic nitrogen present in the form of ammonium. Up to about 80% of all urinary nitrogen is present in many poultry species in the form of organic acids. Almost all of the organic acids are either in the form of uric acid, or in the form of organic acids capable of being converted into uric acid (O'Dell et al., 1960). The organic acid content of a poultry manure containing biomass according to the present invention will therefore contain significant amounts of uric acid which itself is capable of being converted into inorganic ammonium containing compounds, mainly soluble, ammonium containing salts, during a liquid, anaerobic biogas fermentation. Certain ratios, or reactionary relationships, between i) soluble, inorganic ammonium containing compounds present in the fermentation liquid, and ii) ammonia containing fluids and gasses formed during anaerobic biogas fermentation, will develop over time during a continuous, anaerobic liquid state biogas fermentation. These ratios and reactionary relationships will be influenced by - among others - the nature of the biomass as well as the conditions employed for the continuous, anaerobic liquid state biogas fermentation.

The conversion of organic nitrogen sources, such as uric acid, to inorganic nitrogen sources, such as soluble ammonium salts, during a continuous, anaerobic liquid state biogas fermentation will over time result in an increase in the amount of inorganic nitrogen sources present during an anaerobic, liquid state biogas fermentation.

However, an increased amount of inorganic nitrogen compounds in the fermentation liquid during an anaerobic, liquid state biogas fermentation may significantly reduce the biogas yield achieved from the fermentation.

As the inorganic nitrogen compounds present in the fermentation liquid are converted over time into ammonia containing gasses and fluids, and as biogas producing microorganisms are inhibited by high levels of ammonia in a biogas fermenter, the biogas yield will inevitably be significantly reduced over time - unless the development of ammonia containing gasses and fluids is effectively controlled.

Accordingly, various pre-treatment fermentation steps have been suggested in the art for increasing processing and/or removal of both organic and inorganic nitrogen sources from a biomass prior to anaerobic fermentation. While pre-treatment steps, such as e.g. lime pressure cooking, may be acceptable for some complex biomasses containing high amounts of inorganic nitrogen, as well as complex carbohydrate substrates, such as e.g. hemi-cellulose and ligno-cellulose, pre- treatment fermentation steps should be carefully evaluated in terms of both an economical, an ecological, and a commercial value associated with performing pre- treatment fermentation steps.

Another approach aimed at reducing inhibitory levels of nitrogen sources to below critical threshold values in a biomass to be fermented has involved a dilution of the biomass prior to or during anaerobic fermentation - primarily with the objective of reducing inorganic nitrogen levels in the biomass.

Although biomass suspension or dilution may serve to reduce the concentration of undesirable reactants and fermentation by-products, such as e.g. ammonia, a suspension or dilution of a biomass to be fermented also serves to reduce the relative energy-potential of the biomass.

For this reason alone, biomass suspension or dilution is often not a preferred option to consider when aiming to reduce the concentration of undesirable reactants and fermentation by-products, such as e.g. ammonia.

Any dilution of a biomass achieved by adding excessive external sources of aqueous liquids to a biomass will inevitably result in a large excess of aqueous liquids to be disposed of post fermentation, and such disposal can be both costly and cumbersome.

Furthermore, it has surprisingly been observed that certain organic nitrogen

compounds cannot - or only to a very limited extent - be converted into inorganic nitrogen e.g. during thermo-chemical processing steps, including lime pressure cooking step.

Hence, any ammonium sources available for ammonia stripping in a lime pressure cooker is determined exclusively by the amount of inorganic nitrogen which is entered into a lime pressure cooker for ammonia stripping. The inability of a thermo-chemical lime pressure cooking pre-treatment step to convert e.g. organic nitrogen acids into inorganic nitrogen compounds poses a significant challenge to many anaerobic biogas fermentations - as many attractive organic biomass materials contain significant amounts of organic nitrogen sources, including organic acids, which cannot readily be converted into gaseous ammonia during a traditional thermos-chemical lime pressure cooking pre-treatment step.

Accordingly, organic acids, such as e.g. uric acid, represents one form of organic nitrogen which is difficult to convert into organic nitrogen forms, and ultimately into gaseous ammonia fluids, by using conventional, anaerobic fermentation pre-treatment processing steps, such as e.g. thermo-chemical processing steps, including lime pressure cooking.

Poultry manure containing biomasses are both attractive biomass sources and have high contents of uric acid capable of being converted into potentially inhibitory ammonia fluids during anaerobic biogas fermentation.

There continues to exist a need for novel and innovative methods for converting organic acids, including uric acid, present in poultry manure containing biomasses both effectively, and economically and ecologically efficiently, into inorganic nitrogen forms, such as e.g. soluble ammonia salts, and ultimately gaseous ammonia fluids to be removed by stripping from an anaerobic fermenter during a continuous anaerobic, liquid state biogas fermentation. The present invention solves this need and provides a surprisingly simple and efficient method for converting uric acid present in a poultry manure containing biomass into gaseous ammonia fluids without the use of expensive pre-treatment processing steps, such as thermos-chemical pre-treatment, and without diverting excessive amounts of external liquids to an anaerobic fermenter for biomass suspension or dilution.

The poultry manure containing biomasses according to the present invention contain predominantly organic nitrogen sources in the form of organic acids. Uric acid is the most abundant organic acid present in poultry manure, and poultry manure containing biomasses contains total nitrogen sources of which up to as much of approximately 60%, or even as high as about 70% are in the form of uric acid. The high uric acid contents of the poultry manure containing biomasses according to the present invention are initially converted - during an anaerobic biogas fermentation - into inorganic nitrogen containing compounds, including ammonium salts, which are present in the liquid fermentation medium during the anaerobic biogas fermentation, and over time gradually converted into ammonia fluids which can be removed from the anaerobic fermentation unit during the continuous fermentation process.

Accordingly, the present invention provides in preferred aspects thereof:

A method for continuous anaerobic fermentation and formation of biogas;

A method for conditioning a poultry manure containing biomass comprising solid and liquid parts to a form suitable for liquid state continuous anaerobic fermentation and biogas formation; and

A method for reducing the consumption of aqueous liquids for suspension or dilution of a biomass prior to anaerobic fermentation, said method comprising the step of recirculating to an anaerobic fermentation unit a fractionated fermentation liquid comprising fermentation liquid parts and having a reduced content of at least one liquid fermentation by-product, including ammonia and/or soluble inorganic nitrogen compounds, wherein said recirculation makes the anaerobic fermentation unit suitable for conducting a fermentation under anaerobic conditions of a poultry manure containing biomass comprising solid and liquid parts, including uric acid.

The fractionated fermentation liquid comprising fermentation liquid parts and having a reduced content of at least one liquid fermentation by-product, including ammonia and/or soluble inorganic ammonium compounds, can thus be used as a "conditioning agent" suitable for mixing with a poultry manure containing biomass comprising significant amounts of organic acids, including uric acid.

The reduced contents of ammonia and/or soluble inorganic ammonium compounds, including ammonium salts, in the fractionated fermentation liquid can be obtained in accordance with the present invention by performing a series of at least two fractionation steps. In an initial, first fractionation step, anaerobic fermentation liquid comprising one or more liquid fermentation by-products, including inorganic ammonium compounds and ammonia fluids, is diverted from the anaerobic fermentation unit during a continuous anaerobic fermentation to a first separation facility for separation of solid and liquid fractions of the anaerobic fermentation liquid.

Once solid and liquid fractions of the anaerobic fermentation liquid has been generated in the first separation facility, a subsequent and second fractionation step is performed on the liquid fraction obtained from the initial, first fractionation step.

The liquid fraction obtained from the initial, first fractionation step is preferably in the form of a fermented medium liquid fraction comprising fermentation liquid parts comprising one or more liquid fermentation by-products, including soluble inorganic ammonium compounds, and essentially no solid parts.

In the second fractionation step, the fermented medium liquid fraction is diverted from the first separation facility to a second separation facility for separating fluid forms, including ammonia comprising fluids and gasses, and liquid forms, including soluble inorganic ammonium compounds, present in the fermentation liquid parts comprising one or more liquid fermentation by-products.

The second separation step results in the formation of a fermented medium liquid fraction comprising fermentation liquid parts having a reduced content of at least one liquid form, including soluble inorganic ammonium compounds, of a liquid fermentation by-product.

The fermented medium liquid fraction comprising fermentation liquid parts having a reduced content of said at least one liquid form of a liquid fermentation by-product, including soluble inorganic ammonium compounds, is subsequently diverted from the second separation facility back to the anaerobic fermentation unit.

The reduction of the contents of said at least one liquid form, including soluble inorganic ammonium compounds is preferably a reduction of at least 20%, such as at least 30%, for example a reduction of at least 40%, such as at least 50%, for example a reduction of at least 60%, such as at least 65%, for example a reduction of at least 70%, such as at least 75%, for example a reduction of at least 80%, such as at least 85%, for example a reduction of at least 90%, such as at least 95%, for example a reduction of at least 98% of the content of said at least one liquid form of a liquid fermentation by-product, including soluble inorganic ammonium compounds.

Optionally, additional inorganic compounds, including ionic species and/or inorganic salts, are also removed - by filtration, precipitation, or otherwise - from the fermented medium liquid fraction comprising fermentation liquid parts having a reduced content of said at least one liquid form, including soluble inorganic ammonium compounds.

Accordingly, the present invention, in a first aspect thereof, provides a method for anaerobic fermentation and formation of biogas comprising the steps of providing an anaerobic fermentation unit suitable for conducting a continuous liquid fermentation under anaerobic conditions of a poultry manure containing biomass comprising solid and liquid parts, including uric acid; providing a poultry manure containing biomass comprising solid and liquid parts, including uric acid, in a form suitable for continuous liquid state anaerobic fermentation; wherein the poultry manure containing biomass comprising solid and liquid parts, including uric acid, is rendered suitable for continuous, liquid state anaerobic fermentation by addition to the poultry manure containing biomass of a fermented liquid medium fraction comprising fermentation liquid parts having a reduced content of at least one liquid form, including soluble inorganic ammonium compounds, of a liquid fermentation by-product; performing a continuous, liquid state anaerobic fermentation of the poultry manure containing biomass comprising solid and liquid parts in the anaerobic fermentation unit; diverting biogas generated during the continuous, liquid state anaerobic fermentation from the anaerobic fermentation unit to a biogas storage facility; forming liquid and fluid fermentation by-products during the anaerobic fermentation resulting in the formation of said biogas; diverting anaerobic fermentation liquid comprising one or more liquid fermentation by-products from the anaerobic fermentation unit during the continuous, liquid state anaerobic fermentation to a first separation facility for separation of solid and liquid fractions of the anaerobic fermentation liquid; separating solid and liquid poultry manure parts in the first separation facility, wherein said solid and liquid parts are contained in the fermentation liquid comprising the anaerobically fermented biomass and one or more liquid fermentation by-products; thereby obtaining separate fractions of a) a fermented medium solid fraction comprising solid parts from the fermentation liquid, and b) a fermented medium liquid fraction comprising fermentation liquid parts comprising one or more liquid fermentation by-products, including soluble inorganic ammonium compounds, and essentially no solid parts; diverting the fermented medium fraction comprising fermentation liquid parts comprising one or more liquid fermentation by-products, including soluble inorganic ammonium compounds, and essentially no solid parts, to a second separation facility for separating i) fluid forms, including ammonia comprising fluids, and ii) liquid forms, including soluble inorganic ammonium compounds, present in the fermentation liquid parts; subjecting the fermented medium fraction comprising fermentation liquid parts to a pressure and/or a temperature condition in the second separation facility resulting in a reduction of the contents of at least one liquid form of one liquid fermentation by-product, including soluble inorganic ammonium compounds; removing fluid forms, including ammonia comprising fluids, from the fermented medium fraction comprising fermentation liquid parts in the second separation facility; reducing the contents in the fermented medium fraction comprising fermentation liquid parts of at least one liquid form, including soluble inorganic ammonium compounds, of the at least one liquid fermentation by-product; diverting the fermented medium liquid fraction comprising fermentation liquid parts having a reduced content of said at least one liquid form, including soluble inorganic ammonium compounds, of at least one liquid fermentation by-product from the second separation facility back to the anaerobic fermentation unit of step i); and mixing the diverted fermented medium liquid fraction comprising fermentation liquid parts having a reduced content of said at least one liquid form of the at least one liquid fermentation by-product with further poultry manure containing biomass comprising solid and liquid parts, including uric acid; thereby obtaining a poultry manure containing biomass comprising solid and liquid parts, including uric acid, in a form suitable for further continuous liquid state anaerobic fermentation. In another aspect of the present invention there is provided a method for conditioning a poultry manure containing biomass comprising solid and liquid parts, including uric acid, to a form suitable for continuous liquid state anaerobic fermentation and biogas formation, said method comprising the steps of i) providing an anaerobic fermentation unit suitable for conducting a

continuous liquid fermentation under anaerobic conditions of a poultry manure containing biomass comprising solid and liquid parts, including uric acid; providing a poultry manure containing biomass comprising solid and liquid parts, including uric acid, in a form suitable for continuous liquid state anaerobic fermentation; conditioning the poultry manure containing biomass comprising solid and liquid parts, including uric acid, by adding, to the poultry manure containing biomass provided in step ii), a fermented medium liquid fraction comprising fermentation liquid parts having a reduced content of at least one liquid form of a fermentation by-product; wherein said method comprises the further steps of iv) performing a continuous, liquid state anaerobic fermentation of the

poultry manure containing biomass comprising solid and liquid parts in the anaerobic fermentation unit; v) diverting biogas generated during the continuous, liquid state anaerobic fermentation from the anaerobic fermentation unit to a biogas storage facility; vi) forming liquid and fluid fermentation by-products during the anaerobic fermentation resulting in the formation of said biogas; vii) diverting anaerobic fermentation liquid comprising one or more liquid fermentation by-products from the anaerobic fermentation unit during the continuous, liquid state anaerobic fermentation to a first separation facility for separation of solid and liquid fractions of the anaerobic fermentation liquid; separating solid and liquid poultry manure parts in the first separation facility, wherein said solid and liquid parts are contained in the fermentation liquid comprising the anaerobically fermented biomass and one or more liquid fermentation by-products; thereby obtaining separate fractions of a) a fermented medium solid fraction comprising solid parts from the fermentation liquid, and b) a fermented medium liquid fraction comprising fermentation liquid parts comprising one or more liquid fermentation by-products, including soluble inorganic ammonium compounds, and essentially no solid parts; diverting the fermented medium fraction comprising fermentation liquid parts comprising one or more liquid fermentation by-products, including soluble inorganic ammonium compounds, and essentially no solid parts, to a second separation facility for separating i) fluid forms, including ammonia comprising fluids, and ii) liquid forms, including soluble inorganic ammonium compounds, present in the fermentation liquid parts; subjecting the fermented medium fraction comprising fermentation liquid parts to a pressure and/or a temperature condition in the second separation facility resulting in a reduction of the contents of at least one liquid form of one liquid fermentation by-product, including soluble inorganic ammonium compounds; removing fluid forms, including ammonia comprising fluids, from the fermented medium fraction comprising fermentation liquid parts in the second separation facility; reducing the contents in the fermented medium fraction comprising fermentation liquid parts of at least one liquid form, including soluble inorganic ammonium compounds, of the at least one liquid fermentation by-product;, and obtaining a fermented medium liquid fraction comprising fermentation liquid parts having a reduced content of at least one liquid form of at least one liquid fermentation by-product; conditioning further poultry manure containing biomass comprising solid and liquid parts, including uric acid, by adding to said further poultry manure containing biomass the fermented medium liquid fraction comprising fermentation liquid parts having a reduced content of at least one liquid form of at least one fermentation by-product obtained in step xiii); thereby obtaining a conditioned poultry manure containing biomass in the form of a suspension comprising solid and liquid parts, including uric acid, suitable for continuous liquid state anaerobic fermentation; and diverting the poultry manure containing biomass suspension comprising solid and liquid parts suitable for liquid state anaerobic fermentation to the anaerobic fermentation unit provided in step i), and performing a further continuous liquid state anaerobic biogas

fermentation.

In a still further aspect of the present invention there is provided a method for reducing the consumption of external, aqueous liquid sources during continuous anaerobic liquid state biogas fermentation by diverting a fractionated fermentation liquid from an anaerobic fermentation comprising fermentation liquid parts having a reduced content of at least one liquid form of a fermentation by-product to an anaerobic fermentation unit suitable for conducting a continuous liquid state anaerobic fermentation of a poultry manure containing biomass comprising solid and liquid parts, including uric acid, said method comprising the steps of providing an anaerobic fermentation unit suitable for conducting a continuous liquid fermentation under anaerobic conditions of a poultry manure containing biomass comprising solid and liquid parts, including uric acid; providing a poultry manure containing biomass comprising solid and liquid parts, including uric acid, in a form suitable for continuous liquid state anaerobic fermentation; diverting a fractionated fermentation liquid comprising fermentation liquid parts having a reduced content of at least one liquid form of a fermentation by-product back to the anaerobic fermentation unit provided in step i), or diverting said fractionated fermentation liquid to a poultry manure containing biomass comprising solid and liquid parts, including uric acid, to be subjected to anaerobic fermentation; thereby reducing consumption of external aqueous liquids otherwise needed for forming the poultry manure containing biomass provided in step ii); wherein said method comprises the further steps of performing a continuous, liquid state anaerobic fermentation of the poultry manure containing biomass comprising solid and liquid parts in the anaerobic fermentation unit; diverting biogas generated during the continuous, liquid state anaerobic fermentation from the anaerobic fermentation unit to a biogas storage facility; forming liquid and fluid fermentation by-products during the anaerobic fermentation resulting in the formation of said biogas; diverting anaerobic fermentation liquid comprising one or more liquid fermentation by-products from the anaerobic fermentation unit during the continuous, liquid state anaerobic fermentation to a first separation facility for separation of solid and liquid fractions of the anaerobic fermentation liquid; separating solid and liquid poultry manure parts in the first separation facility, wherein said solid and liquid parts are contained in the fermentation liquid comprising the anaerobically fermented biomass and one or more liquid fermentation by-products; thereby obtaining separate fractions of a) a fermented medium solid fraction comprising solid parts from the fermentation liquid, and b) a fermented medium liquid fraction comprising fermentation liquid parts comprising one or more liquid fermentation by-products, including soluble inorganic ammonium compounds, and essentially no solid parts; diverting the fermented medium fraction comprising fermentation liquid parts comprising one or more liquid fermentation by-products, including soluble inorganic ammonium compounds, and essentially no solid parts, to a second separation facility for separating i) fluid forms, including ammonia comprising fluids, and ii) liquid forms, including soluble inorganic ammonium compounds, present in the fermentation liquid parts; subjecting the fermented medium fraction comprising fermentation liquid parts to a pressure and/or a temperature condition in the second separation facility resulting in a reduction of the contents of at least one liquid form of one liquid fermentation by-product, including soluble inorganic ammonium compounds; removing fluid forms, including ammonia comprising fluids, from the fermented medium fraction comprising fermentation liquid parts in the second separation facility; reducing the contents in the fermented medium fraction comprising fermentation liquid parts of at least one liquid form, including soluble inorganic ammonium compounds, of the at least one liquid fermentation by-product;, and obtaining a fermented medium liquid fraction comprising fermentation liquid parts having a reduced content of at least one liquid form of at least one liquid fermentation by-product; diverting the fermented medium liquid fraction obtained in step xiii) back to the anaerobic fermentation unit provided in step i); and/or diverting said fractionated fermentation liquid fraction obtained in step xiii) to a poultry manure containing biomass comprising solid and liquid parts, including uric acid, to be subjected to anaerobic fermentation; thereby reducing consumption of external aqueous liquids otherwise needed for forming the poultry manure containing biomass provided in step ii); wherein said poultry manure containing biomass comprising solid and liquid parts, including uric acid, to be subjected to anaerobic

fermentation is mixed in the anaerobic fermentation unit, or in a mixing tank prior to being diverted to the anaerobic fermentation unit, with the re-diverted, fermented medium liquid fraction obtained in step xiii); thereby obtained a poultry manure containing biomass suspension comprising solid and liquid parts suitable for liquid state anaerobic fermentation; xvi) diverting the poultry manure containing biomass suspension obtained in step xv) to the anaerobic fermentation unit provided in step i), and xvii) performing a further continuous liquid state anaerobic biogas

fermentation.

In various embodiments of the present method, external aqueous liquids are added to poultry manure containing biomass comprising solid and liquid parts, including uric acid, to be subjected to anaerobic fermentation in combination with fermented medium liquid fraction comprising fermentation liquid parts having a reduced content of at least one liquid form of at least one liquid fermentation by-product obtained in step xiii).

In such embodiments of the invention, there are provided a ratio R (vol. / vol.) = i) / ii), wherein i) is volume of fermented medium liquid fraction comprising fermentation liquid parts having a reduced content of at least one liquid form of at least one liquid fermentation by-product obtained in step xiii); and wherein ii) is volume of external aqueous liquids added to poultry manure containing biomass comprising solid and liquid parts, including uric acid, to be subjected to anaerobic fermentation.

In one embodiment, R is preferably in the range of from 2.0:1 to 4.0:1 , such as in the range of from 2.2:1 to 4.0:1 , for example in the range of from 2.3:1 to 4.0:1 , such as in the range of from 2.4:1 to 4.0:1 , for example in the range of from 2.5:1 to 4.0:1 , such as in the range of from 2.6:1 to 4.0:1 , for example in the range of from 2.7:1 to 4.0:1 , such as in the range of from 2.8:1 to 4.0:1 , for example in the range of from 2.9:1 to 4.0:1 , such as in the range of from 3.0:1 to 4.0:1 , for example in the range of from 3.1 :1 to 4.0:1 , such as in the range of from 3.2:1 to 4.0:1 , for example in the range of from 3.3:1 to 4:1 , such as in the range of from 3.4:1 to 4.0:1 , for example in the range of from 3.5:1 to 4.0:1 , such as in the range of from 3.6:1 to 4.0:1 , for example in the range of from 3.7:1 to 4.0:1 , such as in the range of from 3.8:1 to 4.0:1 , for example in the range of from 3.9:1 to 4.0:1 . R may thus also be in the range of from 2.0:1 to 2.2:1 , such as in the range of from 2.2:1 to 2.4:1 , for example in the range of from 2.4:1 to 2.6:1 , such as in the range of from 2.6:1 to 2.8:1 , for example in the range of from 2.8:1 to 3.0:1 , such as in the range of from 3.0:1 to 3.2:1 , for example in the range of from 3.2:1 to 3.4:1 , such as in the range of from 3.4:1 to 3.6:1 , for example in the range of from 3.6:1 to 3.8:1 , such as in the range of from 3.8:1 to 4.0:1 .

Addition of a volume of i), or addition of a volume of ii), or addition of a combined volume of i) and ii), wherein i) is fermented medium liquid fraction comprising fermentation liquid parts having a reduced content of at least one liquid form of at least one liquid fermentation by-product obtained in step xiii); and ii) is external aqueous liquids added to poultry manure containing biomass comprising solid and liquid parts, including uric acid, to be subjected to anaerobic fermentation, is regulated with respect to one or more, including all, of: a) the amount of biomass added to the anaerobic fermentation unit, b) the reaction conditions present in the anaerobic fermentation unit, c) the amount of total ammonia nitrogen present in the biomass to be subjected to anaerobic digestion in the anaerobic fermentation unit, and d) the amount of ammonia stripped from the fermented medium liquid fraction comprising fermentation liquid parts.

Accordingly, adjustment of the above-cited ratios between biomass, externally added aqueous liquids, and re-circulated N-stripped digestate liquids, respectively, will be made to ensure that favorable conditions for methane production in the anaerobic fermentation unit are maintained. Many different factors may affect such favorable conditions for methane production, but no single factor is capable of determining conditions favorable for methane production.

N-stripping constitutes one often very important factor, as stripping of N will prevent formation of inhibitory amounts of ammonia in the anaerobic fermentation unit.

However, N-stripping alone is not sufficient to establish favorable reaction conditions in the anaerobic fermentation unit needed for effective biogas fermentation.

Anaerobic digester fermentation liquids can be separated into digestate solids and effluent liquids e.g. by screw press separation, decanter centrifugation, or any other similarly suitable physical method.

However, the separation process is unable to remove dissolved salts from the resulting effluent liquid streams, and re-circulation of the effluent liquid streams to the anaerobic fermentation unit will result in a re-introduction to the anaerobic fermentation unit of dissolved solids, including salts.

Accordingly, while re-circulation of ammonia stripped digester liquids also contribute to establishing favorable reaction conditions - e.g. by suspension of the biomass to be fermented - re-circulation of ammonia stripped digester liquids will also re-introduce dissolved solids, including salts, to the anaerobic fermentation unit.

Accordingly, it is also important to ensure that the concentration of dissolved solids, including salts, in the anaerobic fermentation unit is kept within certain acceptable limits during operation of the anaerobic digester.

Dissolved solids, including salts, present in fermentation liquids in the anaerobic fermentation unit can be monitored and kept at acceptable levels by continuously adjusting the ratios between i) biomass, ii) aqueous liquids provided from external sources, and iii) re-circulated, ammonia stripped liquid effluents, respectively.

The methods of the present invention are capable of providing from about 100 Nm ³ CH ₄ /ton biomass to about 160 Nm ³ CH ₄ /ton biomass for biomasses having a content of volatile solids (VS) of about 50 %; such from about 1 10 Nm ³ CH ₄ /ton biomass to about 160 Nm ³ CH ₄ /ton biomass for biomasses having a content of volatile solids (VS) of about 50 %; for example from about 1 15 Nm ³ CH ₄ /ton biomass to about 160 Nm ³ CH ₄ /ton biomass for biomasses having a content of volatile solids (VS) of about 50 %; such as from about 120 Nm ³ CH ₄ /ton biomass to about 160 Nm ³ CH ₄ /ton biomass for biomasses having a content of volatile solids (VS) of about 50 %; for example from about 125 Nm ³ CH ₄ /ton biomass to about 160 Nm ³ CH ₄ /ton biomass for biomasses having a content of volatile solids (VS) of about 50 %; such as from about 130 Nm ³ CH ₄ /ton biomass to about 160 Nm ³ CH ₄ /ton biomass for biomasses having a content of volatile solids (VS) of about 50 %; for example from about 135 Nm ³ CH ₄ /ton biomass to about 160 Nm ³ CH ₄ /ton biomass for biomasses having a content of volatile solids (VS) of about 50 %; such as from about 140 Nm ³ CH ₄ /ton biomass to about 160 Nm ³ CH ₄ /ton biomass for biomasses having a content of volatile solids (VS) of about 50 %; for example from about 145 Nm ³ CH ₄ /ton biomass to about 160 Nm ³ CH ₄ /ton biomass for biomasses having a content of volatile solids (VS) of about 50 %; such as from about 150 Nm ³ CH ₄ /ton biomass to about 160 Nm ³ CH ₄ /ton biomass for biomasses having a content of volatile solids (VS) of about 50 %.

As recited herein above, "about" shall signify a maximum deviation of +/- 5 % in the content of volatile solids in the biomass.

In preferred embodiments, the biomass is a poultry manure containing biomass, or a biomass consisting essentially of poultry manure, or a biomass consisting of poultry manure. Furthermore, it is desirable to strip at least about 35% TAN (total ammonia nitrogen) from the fermented medium liquid fraction comprising fermentation liquid parts, such as stripping at least about 40% TAN, for example stripping at least about 42% TAN, such as stripping at least about 44% TAN, for example stripping at least about 46% TAN, such as stripping at least about 48% TAN, for example stripping at least about 50% TAN, such as stripping at least about 52% TAN, for example stripping at least about 54% TAN, such as stripping at least about 56% TAN, for example stripping at least about 58% TAN, such as stripping at least about 60% TAN, for example stripping at least about 62% TAN, such as stripping at least about 64% TAN, for example stripping at least about 66% TAN, such as stripping at least about 68% TAN, for example stripping at least about 70% TAN, such as stripping at least about 72% TAN, for example stripping at least about 74% TAN, such as stripping at least about 76% TAN, for example stripping at least about 78% TAN, such as stripping at least about 80% TAN, for example stripping at least about 82% TAN, such as stripping at least about 84% TAN, for example stripping at least about 86% TAN, such as stripping at least about 88% TAN, for example stripping at least about 90% TAN, such as stripping at least about 95% TAN present in the fermented medium liquid fraction comprising fermentation liquid parts.

The resulting contents of total solids (TS) in the poultry manure containing biomass suspension comprising solid and liquid parts suitable for liquid state anaerobic fermentation is preferably less than about 30% (w/w), such as preferably less than about 28% (w/w), for example preferably less than about 26%, such as preferably less than about 25% (w/w), for example preferably less than about 24%, such as preferably less than about 23% (w/w), for example preferably less than about 22%, such as preferably less than about 21 % (w/w), for example preferably less than about 20%, and preferably more than about 5% (w/w), for example preferably more than about 8%, such as preferably more than about 10% (w/w), for example preferably more than about 1 1 %, such as preferably more than about 12% (w/w), for example preferably more than about 13%, such as preferably more than about 14% (w/w), for example preferably more than about 15%.

The above-cited aspects of the present invention all serve to optimize an efficient fractionation and processing of a poultry manure containing biomass. The above-cited aspects of the present invention also serve to secure an increased production of renewable energy, such as biogas, from anaerobic fermentation of a poultry manure comprising biomass, wherein a post fermentation fractionation of the fermented poultry manure comprising biomass into solid and liquid fermentation medium fractions, and a subsequent processing and re-cycling of the liquid

fermentation medium fraction, ensures an optimal utilization of the utility and energy potential which is present in each of said solid and liquid fermentation medium fractions.

Importantly, the methods of the present invention provide simple, technical solutions for efficiently optimizing anaerobic biomass fermentations and subsequent fractionation and down-stream processing steps conducted on the fermented, poultry manure containing biomasses.

For example, in preferred embodiments of the present invention, there is no need for performing any pre-treatment steps on the poultry manure containing biomass prior to subjecting the poultry manure containing biomass to anaerobic fermentation. Accordingly, poultry manure containing biomass comprising solid and liquid parts, including uric acid, is not subjected to ammonia stripping at elevated temperatures and/or pressure in an ammonia stripping facility prior to being diverted to the anaerobic fermentation unit. Pre-treatment steps which can be avoided in accordance with preferred embodiments of the methods of the present invention also include steps such as for example comminuting the poultry manure containing biomass to be fermented in a comminuting machine, and treating an optionally comminuted poultry manure containing biomass to a pre-anaerobic fermentation processing step, such as e.g. a pre-fermentation step, or a lime pressure cooking step.

The one or more conventional pre-anaerobic fermentation step(s) which can be omitted in accordance with the methods of the present invention include for example the pre- treatment step(s) of poultry manure containing biomass hydrolysis and acetic acid formation based on bacterial interactions with the poultry manure containing biomass in a pre-fermentation unit prior to anaerobic fermentation of the poultry manure containing biomass and biogas production.

In one preferred embodiment, the poultry manure containing biomass is not subjected to a lime pressure cooking pre-treatment step prior to being subjected to anaerobic fermentation in accordance with the methods of the present invention.

Further embodiments of the present invention are disclosed herein below and illustrated in the enclosed drawing. The below further embodiments should be assessed and construed as non-limiting embodiments of the present invention the definition of which should be evaluated as defined by the present patent claims in due consideration of the entirety of the present disclosure.

The present patent claims should not be interpreted as meaning that the extent of the protection conferred is to be understood as that defined by the strict, literal meaning of the wording used in the claims, the description and drawings being employed only for the purpose of resolving an ambiguity found in the claims.

Nor should the present patent claims be interpreted to mean that they serve only as a guideline, and that the actual protection conferred may extend to what, from a consideration of the description and drawings by a person skilled in the art, the patent proprietor has contemplated.

The protection conferred by the claimed scope of the present invention is to be interpreted as defining a position between the above-cited extremes - thereby combining a fair protection for the patent proprietor with a reasonable degree of legal certainty for any third parties.

For the purpose of determining the extent of protection conferred by the present patent claims, due account shall be taken of any element which is equivalent to an element specified in the claims.

The formation of ammonia in a biogas plant - especially at high levels - represents a problem as biogas producing microorganisms in general are sensitive to high levels of ammonia - and high ammonia levels in a biogas fermenter will thus reduce or inhibit the production of methane.

Ultimately, the formation of high levels of ammonia, i.e. above a certain threshold level, cf. below, will kill biogas producing microorganisms, and thereby 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.

It is ammonia (NH ₃ ) which is inhibitory to the biogas production, and 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 formation of gaseous ammonia fluids.

Continuous removal of ammonia fluids from a biomass during biogas fermentation will contribute to a decreased pH value in the fermenter, and it is preferred in accordance with the methods of the present invention that the pH value of an anaerobic biogas fermentation shall be below a pH value of approx. 8,5.

The above-cited technical problems should be taken into consideration when attempts are made to optimize the operation of commercial biogas plants using biomasses, such as e.g. poultry manure containing biomasses, as a substrate for biogas fermenting bacteria, and there continues to be a need for considering how to optimize fermentation of different commercially relevant organic materials, and biomasses comprising or consisting essentially of poultry manures represent one such commercially relevant organic material having a significant potential for biogas fermentation. The present invention solves a number of technical problems presently associated with anaerobic biomass fermentation and biogas production. Energy consumption associated with performing the biomass processing steps of the methods of the present invention has been reduced, and the consumption or redistribution of various natural resources that may often be limited, such as e.g.

aqueous liquids needed for biomass dilution or conditioning, has also been reduced in accordance with the methods of the present invention.

For example, traditional thermo-chemical pre-treatment processing steps, such as e.g. pre-fermentations and energy consuming thermo-chemical biomass processing steps, such as lime pressure cooking steps, can be eliminated in accordance with the principles and methods disclosed in the present invention.

The present invention also serves to increase biogas production by reducing inhibitory levels of ammonia during anaerobic biogas fermentation of a poultry manure containing biomass. Poultry manure containing biomasses represent one preferred "input" biomass for use in the methods of the present invention. Most of the N (from about 50 to 75%) present in poultry manure containing biomasses according to the present invention is in the form of uric acid and proteins. Additionally preferred 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.

Biomasses according to the present invention have high contents of organic nitrogen (N) and/or inorganic nitrogen (N) sources, including uric acid, urea and ammonia, and the biomasses may comprise e.g. solid manure waste products from e.g. in particular poultry farms, as well as manure waste products from facilities such as e.g. dairies, slaughterhouses, and meat processing industries in general, as wells as energy crops and or other plants. In accordance with the methods of the present invention, nitrogen mineralisation levels range from about 50% to as much as about 85% conversion of the total organic nitrogen fraction.

Uric acid nitrogen constitutes from about 40% to about 65% of the organic nitrogen fraction, and the conversion of uric acid in the poultry manure containing biomasses subjected to anaerobic fermentation as well as the subsequent fractionation and processing steps, including ammonia stripping, is essentially complete. Conversion of remaining organic nitrogen fraction, primarily protein bound nitrogen, in the poultry manure containing biomasses according to the present invention ranges from about 40% or 50% to as much as about 75%.

It is preferred that the conversion of protein bound nitrogen in the remaining organic nitrogen fraction in the poultry manure containing biomasses according to the present invention is optimized - i.e. that an amount of protein bound nitrogen is converted to inorganic ammonia N in such a way that the energy needed for achieving this conversion is optimized. Typically, organic N to ammonia N conversion rates of at least 50%, such as preferably at least about 60 % should be achieved.

Bioqas fermentation

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. Many biogas 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.

Accordingly, 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 15 days to preferably less than 45 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 45°C to 75°C, such as fx a reaction temperature ranging from 55°C to 60°C.

Organic N is converted to ammonia N during the process of generating biogas by anaerobic fermentation, and conversion of as much as approx. 40 % to 80 % of organic N to ammonia N can be achieved in accordance with the present invention. Most of this conversion takes place during the anaerobic fermentation itself. Accordingly, in one embodiment of the present invention, conversion of from 40 % to 80 % of organic N to ammonia N is achieved in accordance with the methods of the present invention.

When employing e.g. a biomass essentially consisting of poultry manure, it is possible in accordance with the methods of the present invention to remove from the poultry manure containing biomass up to as much as about 40 to 85 % of the ammonia N present in the poultry manure. The removal of ammonia N primarily takes place when fractionated poultry manure containing biomass in the form of fermentation medium liquid fractions containing essentially no solid parts are subjected to an ammonia stripping step prior to being diverted back to the anaerobic fermentation unit.

Approximately 30% to 50% of all N in poultry manure containing biomass according to the present invention is in the form of ammonium N, but poultry manure is also rich in uric acid, and uric acid is not converted - or only converted very inefficiently - to ammonia N during e.g. a lime pressure cooking pre-treatment step.

In view of the above, there is a need for devising a strategy for increasing the nitrogen conversion in biomasses comprising high amounts of organic N, such as e.g. uric acid, into inorganic N forms, such as e.g. liquid ammonium N forms which can be converted into ammonia N fluids under suitable conditions.

There is also a need for devising improved methods for the conversion of biomasses comprising high amounts of uric acid into ammonium N and biogas, and for efficient fermentation of such biomasses able to secure increased amounts of biogas while solving at the same time the challenge of ammonia inhibition.

However, particular challenges arise, cf. above, when it is desirable to process organic materials having a particularly high N content - as inhibitory levels of ammonia during biogas fermentation can be expected to occur relatively early on in the fermentation process due to the high levels of organic N and protein in the organic material to be processed.

Although it is indeed possible to obtain, following anaerobic fermentation in accordance with the methods of the present invention, a conversion of organic bound N to inorganic N of up to 70 to 80 %, lower conversion values can also be obtained depending on the anaerobic fermentation conditions and the contents of organic N in the poultry manure containing biomass to be fermented, such as for example conversion rates of approx. 35%, approx. 40%, approx. 45%, approx. 50%, approx. 55%, approx. 60%, and

approx. 65%. This will generally depend on the reaction conditions employed for the anaerobic biogas fermentation. In one embodiment, 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 the anaerobic biogas fermentation e.g. operated under the conditions disclosed herein above.

In view of the above-cited technical problems, the present invention provides in one aspect thereof an improved technical solution to the problem of how to improve biogas production in a commercial biogas plant.

The anaerobic fermentation resulting in the production of biogas may be performed by anaerobic digestion of a biomass comprising significant amounts of poultry manures in combination with a series of processing steps aimed at separating the digestate fibrous fraction from a fermentation medium liquid fraction, stripping ammonia N from the fermentation medium liquid fraction when this liquid fraction has been separated from the solid fraction digestate during a continuous biogas fermentation, and re-diverting the ammonia-stripped fermentation liquid to the anaerobic digester, or, alternatively, re- diverting the ammonia-stripped fermentation liquid to a mixing tank for mixing with further biomass, including poultry manure containing biomasses, to be subjected to anaerobic digestion.

According to one embodiment of the above-cited aspect of the present invention, an anaerobically fermented biomass comprising or essentially consisting of poultry manures is separated into a solid digestate and a fermentation medium liquid fraction, and the liquid fraction comprising ammonia N is subjected to an ammonia stripping step - prior to the stripped fermentation medium liquid fraction being re-diverted to the anaerobic digester, or, alternatively, re-diverted to a mixing tank for mixing with further biomass, such as or including poultry manure containing biomasses to be subjected to anaerobic digestion and biogas production.

Fractionation of fermentation medium during continuous anaerobic biogas fermentation

In one embodiment according to the methods of the present invention, fermentation medium comprising solid and liquid parts is fractionated using a decanter centrifuge. The decanter centrifuge secures fractionation of fermentation medium into liquid and solid fractions, wherein the solid fraction contains up to about 60% to 80% dry matter, including from about 40-80% of total phosphor (P) present in the fermentation liquid, but only as little as about less than 15% of total ammonia N (Moller et al. 1999; Moller 2000a).

Decanter centrifugation thus not only ensures an effective separation of solid and liquid fermentation medium fractions, the centrifugation also ensures a separation of valuable nutrients.

Digestate separation is carried out prior to ammonia stripping, and the separation is preferably a physical separation obtained e.g. by use of a decanter centrifuge. The separation of solid and liquid parts reduces the contents of fibers and other solid parts in the liquid phase which is diverted to the ammonia stripper. Reduced contents of fibers and other solid parts in the liquid phase will reduce the risk of clogging of the ammonia stripper system. Also, removal of fibers from the liquid phase may also serve to increase ammonium-N in the liquid phase. In one embodiment, fermentation medium comprising solid and liquid parts to be fractionated using the decanter centrifuge may be treated with lime in order to increase pH and increase the amount of total phosphor (P) present in the solid fraction of the fermentation liquid. Accordingly, following decanter centrifugation, a phosphor (P) rich solid fraction can be obtained which has a substantial commercial value.

As the phosphor (P) rich solid fraction obtained following decanter centrifugation contains relatively small amounts of nitrogen N, it does not make process economical sense to subject the liquid biomass to an ammonia stripping step.

However, the phosphor (P) rich solid fraction has a number of other valuable uses, including the use as a fertilizer supplement in crop field management, and as a nutrient for cultivating various edible foods, including various mushrooms (cf. e.g. Chanakya et al. (2015)). Ιί has been reported by Chanakya, ibid., that e.g. P!eurotus species can be cultivated on different agro-residues in combination with biogas fermentation residue, and addition of the biogas fermentation residue to the agro-residues was reported to increase Pleurotus mushroom yields by as much as 20 to 30%,

Accordingly, rather than being traditionally perceived as relatively low-value crop fertilizer, the fractionated, solid fermentation medium according to the present invention actually constitutes a high-value nutritional supplement for direct use in the cultivation of edible foods, such as edible mushrooms.

Stripping of ammonia N from fermentation medium liquid fraction(s) Ammonia can be stripped from a fermentation medium liquid fraction according to the present invention in different ways in accordance with methods generally available in the prior art.

Removal of ammonia from an organic biomass by stripping is generally a matter of temperature, alkalinity and airflow, and factors such as temperature, alkalinity and ventilating airflow must be taken into consideration when optimizing the stripping of ammonia from an organic biomass in general, or from the fermentation medium liquid fraction according to the present invention. An increased temperature will shift the equilibrium from soluble ammonium salts to gaseous ammonia - and gaseous ammonia can be stripped and collected essentially as described in the prior art.

One principle for large scale stripping of ammonia from e.g. a biomass comprising or essentially consisting of poultry manures - or from a fermentation medium liquid fraction - is to increase the pH in combination with aerating and/or heating of the biomass or the fermentation medium liquid fraction.

Ammonia stripping can fx occur at ambient pressure, in a vacuum, as well as under increased pressure, such as a pressure above 1 bar. 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 or above 1 atm.

Ca(OH) ₂ or CaO, collectively referred to as lime, can be used to increase the pH in an ammonia stripping step. Lime is cheap and readily available as a bulk product. Other bases may also be employed, such as e.g. NaOH or KOH.

Stripped ammonia can be absorbed, and an ammonia concentrate can be produced. This may be done by diverting stripped ammonia e.g. to a sulphuric acid solution 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 suitable for stripping ammonia from slurries and waste waters.

In one embodiment of the present invention, a liquid stripper and an ammonia scrubber/washer system is provided for stripping ammonia. Recirculated air saturated with ammonia is diverted - in a counter-flow orientation with respect to the incoming, fractionated fermentation liquid - through a stripper column, and subsequently washed with sulphuric acid in a scrubber before being re-circulated one or more times.

A relatively low energy consumption is required for operating the air blowers of the stripper system, and the ammonia stripping requires only a minimal heating input in addition to heating inputs required for compulsory hygienization and heating of anaerobic digester contents.

In the present invention, stripping of ammonia, including air stripping, is carried out exclusively on the liquid fraction of the digestate after removal of the fiber fraction. This means that the stripper columns of an ammonia scrubber/washer system can be operated with a minimized risk of clogging, and the ammonia removal efficiency achieved in this way is sufficient to ensure fermentation conditions in the anaerobic digester which are not inhibited by undesirably high ammonia levels.

Air stripping of ammonia from liquid phase digestate after removal of solid parts is preferred due to lower complexity, lower capital expenditures (CAPEX), and lower operating expenses (OPEX) compared for example to more complex, and more costly, thermo-alkaline processes operated at elevated pressures. In another embodiment, the present invention provides an ammonia stripping step which is preferably being carried out by using a steam stripper operated at ambient pressure. The stripper principle benefits form the different boiling temperatures of ammonia and water. At temperatures close to 100°C extraction of ammonia is most efficient.

The use of energy in order to heat the fermentation medium liquid fraction diverted to the steam stripper is an essential running parameter. The stripper unit pre-heats the fermentation medium liquid fraction to a temperature in the range of from about 45°C to preferably less than 100°C before this fraction is being diverted into the stripper column.

Heated fermentation medium liquid fraction enters the stripper column and percolates over the column while at the same time being heated to the running temperature by a counter current of free steam. The steam/ammonia gas is subsequently condensed in a one or two step condensator.

Fermentation medium liquid fraction stripped of ammonia as well as other liquid fermentation medium volatile by-products can be pumped from the floor of the stripper column by an exit pump.

The stripped ammonia is diverted to the bottom of e.g. a two-step scrubber

condensator in which ammonia gas is condensed primarily in a counter current of cooled ammonia condensate.

Any ammonia gas not condensed in a first round concensation step may subsequently be condensed in a counter current of pure water. If use of acid is deemed desirable, or necessary, it is appropriate to use sulphuric acid at this stage. It is thereby possible to achieve a higher final concentration of ammonia.

A condensate scrubber can be used in order to gain flexibility concerning addition of acid. The column is preferably constructed in two sections so that the fraction of ammonia which is not condensed in the first section is subsequently condensed in the second section. Condensation takes place in a full counter current so that addition of water is limited as much as possible. A maximum ammonia concentration in the final condensate of more than 25%, such as more than 30%, may be achieved. The ammonia containing condensation product can be pumped out with a separate pump, or the product can be taken out from a valve on the circulation pump. The absorption may be assisted by addition of sulfuric acid into the water counter current.

The present invention in another embodiment of ammonia stripping provides a method and a system for stripping ammonia from fermentation medium liquid fractions comprising ammonia or precursors thereof. This embodiment is illustrated in Figure 2. Part of the ammonia is stripped from the fermentation medium liquid fractions in a stripper system comprising a shunt through which fermentation medium liquid fractions can be diverted. The stripper system is connected to an evaporator. In the evaporator aqueous liquid is heated at a pressure below atmospheric pressure whereby vapour is developed at a temperature below 100°C.

The ammonia vapours from the evaporator are directed to a liquid medium, and ammonia is stripped from the liquid medium in another vapour phase. The vapour phase is condensed in a first condenser at a low pressure, e.g. a pressure below 1 bar, such as a pressure of less than 0.5 bar, and the liquid thus obtained can be further treated in a stripper unit using a higher pressure, such as e.g. a pressure at or above 1 bar, but preferably below 5 bar. This form of processing results in the generation of more concentrated ammonia comprising fluids or liquids. When stripped for at least a substantial part of the ammonia, the stripped fermentation medium liquid fraction can be diverted back to the anaerobic fermentation unit, or diverted to essentially solid poultry manure containing biomasses which need to be suspended in liquids prior to anaerobic digestion. An optimal water balance in the anaerobic digester(s) may be maintained by adjustment, and diversion to the anaerobic digester(s), of the respective amounts of recycled liquid digestate, and an external water source, respectively, which are needed for maintaining optimal anaerobic fermentation conditions. Also, the relative amounts of the external water source being diverted to the anaerobic digester(s) are in principle being diverted independently of the ammonia concentration in the digester(s), as said ammonia concentration can e.g. be controlled by other means, such as e.g. by reducing further the ammonium-N concentration in the liquid digestate, and/or by increasing the rate of the recycling.

According to one presently preferred hypothesis, parameters seemingly affecting an optimal, external water source dilution rate seem to be the related to the total concentration of salts, including the concentration of potassium (K). These parameters are not influenced by the choice of stripping method, or by the location of the stripper system within the overall fermentation system.

One working principle of the above-disclosed stripping of inorganic ammonia sources in a fermentation medium liquid fraction is disclosed in EP 1 528 953. The working principle is further explained herein below, and illustrated in Fig. 2.

The working principle is based on cold steam and vacuum and involves a first condensing device (K1 ). This step generates a first condensed aqueous liquid and a vapour not condensed by the first condensing device. The first condensing device operates at a low pressure below a predetermined reference pressure, preferably a reference pressure of 1 bar.

Vapour not condensed by the first condensing device is optionally diverted in a further process step to a further condensing device (K2) at a pressure below the

predetermined reference pressure. The objective is to remove a substantial part of the remaining volatile compounds, such as e.g. ammonia, from said vapour not condensed by the first condensing device. The objective is achieved by including a washing step using a counter current of aqueous liquid, obtaining an aqueous liquid fraction comprising volatile compounds, such as e.g. ammonia, and optionally also vapour not condensed by the further condensing device.

A further process step comprises diverting said first condensed aqueous liquid from K1 , and optionally also said aqueous liquid fraction from K2, comprising volatile

compounds, such as e.g. ammonia, from the first condensing device, and optionally also from the further condensing device, to a stripper unit (K3), where said condensate(s) are stripped of volatile compounds, such as e.g. ammonia, by heating the condensate(s) at a second pressure which is higher than the first pressure, preferably a pressure of 1 bar or more, and obtaining a hot volatile compound stream, such as e.g. an ammonia comprising steam, and aqueous liquids, such as fermentation medium liquid fractions stripped of a substantial part of volatile compounds contained in said fermentation medium liquid fractions, such as e.g. ammonia.

The higher second pressure is obtained by heating the liquid medium comprising the aqueous liquid fraction from K2 comprising volatile compounds, such as e.g. ammonia, and optionally also the first condensed aqueous liquid medium from K1 comprising volatile compounds, such as e.g. ammonia, in the stripper unit K3 to a temperature of more than 100°C, such as more than 105°C, for example more than 1 10°C, such as more than 1 15°C, for example more than 120°C, such as more than 125°C, for example more than 130°C, such as more than 135°C, for example more than 140°C, such as more than 145°C, for example more than 150°C, such as more than 155°C, for example more than 160°C, such as more than 165°C, for example more than 170°C, such as more than 175°C, for example more than 180°C, such as more than 190°C, for example more than 200°C, and preferably less than 250°C. In a preferred embodiment, a fermentation medium liquid fractions are continuously pumped to a separation unit, or shunt (S), in which cold steam at a temperature of from about 50°C to about 65°C, such as from about 55°C to about 65°C, for example from about 60°C to about 65°C, such as from about 50°C to about 60°C, for example from about 50°C to about 55°C, such as from about 55°C to about 60°C, for example from about 57°C to about 62°C, such as about 60°C, is held under a vacuum of from about 0.05 to about 0.4 bar, for example from about 0.1 bar to about 0.4 bar, such as from about 0.15 bar to about 0.4 bar, for example from about 0.2 bar to about 0.4 bar, such as from about 0.25 bar to about 0.4 bar, for example from about 0.30 bar to about 0.4 bar, such as from about 0.35 bar to about 0.4 bar, for example from about 0.05 bar to about 0.35 bar, such as from about 0.05 bar to about 0.3 bar, for example from about 0.05 bar to about 0.25 bar, such as from about 0.05 bar to about 0.2 bar, for example from about 0.05 bar to about 0.15 bar, such as from about 0.05 bar to about 0.1 bar, for example from about 0.1 bar to about 0.15 bar, such as from about 0.15 bar to about 0.2 bar, for example from about 0.2 bar to about 0.25 bar, such as from about 0.25 bar to about 0.3 bar, for example from about 0.3 bar to about 0.35 bar, such as from about 0.35 bar to about 0.4 bar, depending on the running conditions.

The cold steam obtained in the evaporator (E) is directed through a liquid medium comprising the fermentation medium liquid fraction in the shunt / separator (S), which is equipped with diffusers. While contacting the fermentation medium liquid fraction, the steam strips off volatile compounds such as e.g. ammonia.

The generated vapour/steam comprising volatile compounds, such as e.g. ammonia, preferably comprises about 1 -10% volatile compounds such as e.g. ammonia, such as 2-10% volatile compounds such as e.g. ammonia, for example 3-10% volatile compounds such as e.g. ammonia, such as 4-10% volatile compounds such as e.g. ammonia, for example 5-10% volatile compounds such as e.g. ammonia, such as 5-9% volatile compounds such as e.g. ammonia, for example 5-8% volatile compounds such as e.g. ammonia, such as 5-7% volatile compounds such as e.g. ammonia, such as 6- 10% volatile compounds such as e.g. ammonia, for example 7-10% volatile

compounds such as e.g. ammonia, such as 8-10% volatile compounds such as e.g. ammonia, for example 9-10% volatile compounds such as e.g. ammonia, such as 1 -9% volatile compounds such as e.g. ammonia, for example 1 -8% volatile compounds such as e.g. ammonia, such as 1 -7% volatile compounds such as e.g. ammonia, for example 1 -6% volatile compounds such as e.g. ammonia, such as 1 -5% volatile compounds such as e.g. ammonia, for example 1 -4% volatile compounds such as e.g. ammonia, such as 1 -3% volatile compounds such as e.g. ammonia, for example 1 -2% volatile compounds such as e.g. ammonia, such as 2-4% volatile compounds such as e.g. ammonia, for example 4-6% volatile compounds such as e.g. ammonia, such as 6- 8% volatile compounds such as e.g. ammonia, for example 8-10% volatile compounds such as e.g. ammonia, such as 2-3% volatile compounds such as e.g. ammonia, for example 3-4% volatile compounds such as e.g. ammonia, such as 4-5% volatile compounds such as e.g. ammonia, for example 5-6% volatile compounds such as e.g. ammonia, such as 6-7% volatile compounds such as e.g. ammonia, for example 7-8% volatile compounds such as e.g. ammonia, such as 8-9% volatile compounds such as e.g. ammonia.

This steam is subsequently condensed at a low, first pressure (in K1 ) and further concentrated (stripped) at higher second pressure (in K3) to achieve preferably a solution of as much as 25% volatile compounds such as e.g. ammonia in aqueous liquid, such as for example 22% volatile compounds such as e.g. ammonia in aqueous liquid, for example 20% volatile compounds such as e.g. ammonia in aqueous liquid, for example 18% volatile compounds such as e.g. ammonia in aqueous liquid, for example 16% volatile compounds such as e.g. ammonia in aqueous liquid, for example 14% volatile compounds such as e.g. ammonia in aqueous liquid, for example 12% volatile compounds such as e.g. ammonia in aqueous liquid, for example 10% volatile compounds such as e.g. ammonia in aqueous liquid, for example 8% volatile compounds such as e.g. ammonia in aqueous liquid, and preferably a solution of more than 5% volatile compounds, such as e.g. ammonia, in an aqueous liquid.

Plant for generating bioqas

In another aspect of the present invention there is provided a closed-circuit

continuously operating plant for generating biogas from a continuous, liquid anaerobic fermentation of a biomass comprising poultry manures, said plant comprising: i) one or more fermenters for performing a continuous, anaerobic liquid state biomass fermentation; ii) a first separation unit directly connected to one of said fermenters, wherein said first separation unit is capable of separating fermented biomass a solid organic material fraction and a fermentation medium liquid fraction comprising one or more liquid sources of nitrogen; iii) means for diverting said fermentation medium liquid fraction comprising one or more liquid sources of nitrogen to an ammonia stripping facility; and iv) a second separation unit comprising an ammonia stripping facility for stripping ammonia from said fermentation medium liquid fraction comprising one or more liquid sources of nitrogen, wherein said first and second separation units are directly connected to each other; wherein said second separation unit is directly connected to said one or more fermenters; an absorption unit for absorbing and condensing ammonia fluids diverted to the absorption unit from the ammonia stripping facility; means for diverting fermentation medium liquid fractions stripped for one or more liquid sources of nitrogen to one or more of said fermenters for performing in said fermenters a continuous, anaerobic liquid state fermentation of a solid biomass; wherein the connections between said one or more fermenters and said first and second separation units provides a closed-circuit anaerobic fermentation unit for performing anaerobic liquid state fermentations on a continuous basis; wherein the only external medium diverted into the closed-circuit anaerobic fermentation unit is further biomass to be fermented, and wherein the only medium diverted from the closed-circuit anaerobic fermentation unit to an external environment is spent digestate obtained from the separation of fermented biomass in the first separation unit.

The bioenergy plant may further comprise a mixing tank for mixing the ammonia stripped, fermentation medium liquid fraction with a further biomass to be subject to anaerobic fermentation, and the mixing tank is operably connected in one embodiment to a reception station suitable for receiving solid organic biomaterial and/or operably connected to a reception tank suitable for receiving liquid organic biomaterial.

Also, the mixing tank is in one embodiment further operably connected to an absorption unit for absorbing and condensing ammonia fluids, wherein said connection allows ammonia to be stripped in the mixing tank and diverted to the absorption unit. The absorption unit for absorbing and condensing ammonia fluids diverted to the absorption unit from the mixing tank is preferably the same absorption unit which is operably connected to the ammonia stripping facility of the second separation unit as described herein above in more detail. The absorption unit for absorbing and condensing ammonia fluids in one embodiment preferably comprises a steam condenser and a scrubber as described herein above in more detail.

The bioenergy plant comprises one, and preferably more than one, fermenters for anaerobically fermenting the poultry manure containing biomass, wherein said one or more than one fermenters are serially connected so that poultry manure containing biomass having been fermented in a first fermenter under a first set of fermentation conditions can subsequently be diverted to a second or further fermenter and fermented therein under a second or further set of fermentation conditions.

The fermentation medium liquid fraction is obtained by removing fermentation medium digestate from the fermentation medium diverted from the one or more anaerobic biogas reactors to the first separation unit. This can be achieved in a number of ways according to state-of-the-art methods. The first separation unit in one embodiment comprises a decanter centrifuge as described herein above in more detail.

It is preferred that the one or more than one anaerobic fermenters comprise 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 anaerobic fermenters.

When the plant comprise more than one fermenter for anaerobically fermenting said organic materials, said more than one fermenters are preferably 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 fermenters preferably comprise 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. Description of the Drawings Figure 1 illustrates preferred principles and method steps of the present invention.

An organic biomass containing both organic and inorganic sources of nitrogen, such as for example poultry manure containing biomass comprising solid and liquid parts in a form suitable for liquid state anaerobic fermentation, is diverted to an anaerobic fermentation unit suitable for conducting a fermentation under anaerobic conditions e.g. of poultry manure containing biomass comprising solid and liquid parts.

A continuous anaerobic biogas fermentation of e.g. poultry manure containing biomass comprising solid and liquid parts is performed in the anaerobic fermentation unit, and biogas generated during the fermentation is diverted - during the continuous anaerobic fermentation - from the anaerobic fermentation unit to a biogas storage facility.

Liquid and fluid fermentation by-products are formed during the anaerobic biogas fermentation, and such by-products are contained in the fermented biomass which is continuously diverted from the anaerobic fermentation unit to a first separation facility.

Accordingly, anaerobic fermentation liquid comprising one or more liquid fermentation by-products is diverted from the anaerobic fermentation unit during the continuous anaerobic fermentation to a first separation facility for separation of solid and liquid fractions of the anaerobic fermentation liquid.

Solid and liquid biomass parts, such as e.g. solid and liquid poultry manure parts, are separated in the first separation facility, and separate fractions of i) a fermented medium fraction comprising solid parts from the fermentation liquid, and ii) a fermented medium fraction comprising fermentation liquid parts comprising one or more liquid fermentation by-products, and essentially no solid parts, are formed by the separation of the solid and liquid parts.

The solid parts are primarily in the form of a digestate or a fibrous fraction primarily containing organic nitrogen sources suitable for use as a fertilizer. The liquid parts of the fermentation liquid, in the form of a fermented medium fraction comprising fermentation liquid parts comprising one or more liquid fermentation byproducts, and essentially no solid parts, are diverted to a second separation facility, such as a stripper tank, for separating fluid and liquid forms of any one or more liquid fermentation by-products present in the fermented medium fraction comprising fermentation liquid parts.

The fermented medium fraction comprising fermentation liquid parts comprising one or more liquid fermentation by-products, and essentially no solid parts, contain organic and inorganic nitrogen sources.

The fermented medium fraction is subjected - in the second separation facility for separating fluid and liquid forms of any one or more liquid fermentation by-products present in the fermented medium fraction comprising fermentation liquid parts - to a pressure and/or a temperature condition resulting in an increased fluid form to liquid form ratio of at least one liquid fermentation by-product present in the fermented medium fraction comprising fermentation liquid parts. The fermentation by-products of ammonium / ammonia are thus present in these liquid / fluid forms.

At least one fluid form of at least one liquid fermentation by-product, such as ammonia, is removed from the fermented medium fraction comprising fermentation liquid parts in the second separation facility. Fluid form by-products can be removed from the fermented medium fraction comprising fermentation liquid parts according to any state- or-the-art method for removing such volatile fluid form by-products, including ammonia.

In Fig. 1 , ammonia is removed following addition of lime, but this step is optional, and it may well be sufficient to increase the temperature and/or the pH of the fermented medium fraction comprising fermentation liquid parts in order to achieve a removal of volatile fluid form by-products, including ammonia.

Removal of volatile fluid form by-products, including ammonia, results in a reduction in the fermented medium fraction comprising fermentation liquid parts of at least one liquid form of at least one liquid fermentation by-product, such as ammonium. The fermented medium fraction comprising fermentation liquid parts and having a reduced content of said at least one liquid fermentation by-product, including ammonium, is re-diverted or re-cycled from the second separation facility to the anaerobic fermentation unit.

The re-diverted or re-cycled fermented medium fraction comprising fermentation liquid parts and having a reduced content of said at least one liquid fermentation by-product, including ammonium, is mixed with a further poultry manure containing biomass comprising solid and liquid parts which has been diverted to the anaerobic fermentation unit.

Alternatively, the re-diverted or re-cycled fermented medium fraction comprising fermentation liquid parts and having a reduced content of said at least one liquid fermentation by-product, including ammonium, is mixed with a further poultry manure containing biomass comprising solid and liquid parts before the combined mixture thereof is diverted to the anaerobic fermentation unit.

Mixing of re-diverted or re-cycled fermented medium fraction comprising fermentation liquid parts and having a reduced content of said at least one liquid fermentation by- product, including ammonium, with a further poultry manure containing biomass comprising solid and liquid parts ensures that a poultry manure containing biomass comprising solid and liquid parts is provided in or to the anaerobic fermentation unit in a form suitable for liquid state anaerobic biogas fermentation. By re-diverting or re-cycling the fermented medium fraction comprising fermentation liquid parts and having a reduced content of said at least one liquid fermentation byproduct, including ammonium, to the anaerobic fermentation unit, the anaerobic biogas fermentation can be operated on a continuous basis essentially without the addition of further sources of aqueous liquids.

The re-diversion or re-cycling of the liquid fermented medium fraction to the anaerobic fermentation unit thus serves the dual purposes of i) conditioning the poultry manure containing biomass for anaerobic biogas fermentation, and ii) eliminating the need for diversion of excessive amounts of external sources of aqueous liquids to the anaerobic fermentation unit in order to dilute out excessive amounts of organic and/or inorganic nitrogen sources in the biomass. In combination with the above-cited advantages of the present invention, organic and/or inorganic nitrogen sources are reduced in and/or removed from the fermented medium fraction comprising fermentation liquid parts in the second separation unit prior to a fermented medium liquid fraction having a reduced content of said at least one liquid fermentation by-product, including ammonium, being re-diverted or re-cycled to the anaerobic fermentation unit.

As the solid, fibrous fraction of the fermentation liquid has already been removed from the fermented medium fraction comprising fermentation liquid parts in the first separation unit, any energy needed for subjecting the fermented medium fraction diverted to the second separation facility for separating fluid and liquid forms of any one or more liquid fermentation by-products present in said fermented medium fraction, to a processing step involving an increased temperature, an increased pressure, or an increased pH, including any combination thereof, can be optimized.

For example, a heating step in the second separation unit will require energy for heating only the fermentation liquid from which the solid, fibrous fraction has already been removed in the first separation unit.

Accordingly, selectively heating only the fermented medium liquid fraction diverted to the second separation facility for separating fluid and liquid forms of any one or more liquid fermentation by-products present in said fermented medium fraction, serves to preserve energy and avoids using energy for heating the solid fibrous fraction.

Fig. 2 illustrates one embodiment of an ammonia stripping facility according to the present invention. The device comprises a first stripping unit (2) and a second stripping unit (7), said units being connected by conduits so that vapour, here about 5% by weight of NH ₃ at about 50 °C, from the first stripping column (2) is condensed by a first condenser (4). Subsequently the condensate and vapour is separated into a condensed phase and a vapour phase at said reduced pressure in a phase separator (5). The condensed phase, here about 5% by weight of NH ₃ at about 30-40 °C, is pumped to said second stripping unit (7) at a reference pressure, here atmospheric pressure (1000 kPa), by means of pump (9). In the second stripping unit, the condensed phase is further stripped to produce a vapour of about 25% by weight of NH3 at a temperature of about 80 °C in the top of the second stripping column.

Subsequently this vapour phase is condensed in a second condenser (8) to a temperature at about 30 °C. The liquid to be treated, here liquid of manure from an organic waste water treatment plant producing bio gases and treating liquids of manure, is let into said first stripping column (2) through a reduction valve (1 ) at a temperature of about 60°C. The first stripping unit (2) comprises a stripping container (3) for producing a vapour of volatile components from the liquid at a reduced pressure, here e.g. 200 to 800 hPa below a predetermined reference pressure, here preferably atmospheric pressure. Heat is supplied by a heating means; here a heat exchanger placed at the bottom end of the stripping column (2), which heat exchanger here uses cooling water from the biogas production section of organic waste water treatment plant. The stripping container is preferably a stripping column the characteristics of which has been design according to methods known in the art, including but not limited to designs based on the commercial software design package Hyses™. Typically, it is preferred to use stripping columns having 8-12 theoretical plates. A practical construction of such a stripping column, including design of column plates, inter-plate conduits, selection of column package materials, etc., is known to a person skilled in the art. Commercial stripping columns are generally available from chemical engineering suppliers.

Selecting a proper balance between the energy sources available at the plant site, e.g. either a source of low valued energy such as cooling water or a high valued energy such as combustion heat or electricity, and the involved temperatures and pressures in generating the vapour and condensate, a skilled person can provide an optimum design for the apparatus for vapour stripping of volatile components from a liquid, e.g. for generating vapour of said volatile components. In a preferred embodiment of the apparatus, heat at about 80°C is supplied to the column at a rate providing a warm vapour of about 5% by weight of NH ₃ at a temperature of about 50 °C at the outlet of the column and of a pressure of about 200 kPa. A residue is taken out of the stripping column, here at the bottom thereof. A first condenser (4), here a plate type condenser especially suited to resist basic conditions of ammonia which is generally available from chemical engineering suppliers, is used for condensing said vapour of volatile components from said stripping container at said reduced pressure.

A phase separator (5) separates said condensed volatile components and said vapour of volatile components from said first condenser (4) into a condensed phase and a vapour phase at said reduced pressure. At least one vapour evacuation pumps (6), here preferably a displacement pump generally available from chemical engineering suppliers, is used for removing dissolved gasses such as carbon dioxide and nitrogen and producing a reduced pressure below said reference pressure; said vapour evacuation pumps being positioned down stream said first condenser. Vapour gasses are taken out from the vapour phase of the phase separator (5) to final scrubbing before being released to the atmosphere (not shown).

Said a second stripping unit (7) comprises a second stripping container (7) for producing a vapour of volatile components from said condensed phase at said predetermined reference pressure.

The second stripping container preferably consists of a stripping column which preferably is prepared by same and/or similar methods and means to those used for making said first stripping column (2), with the exception that considerations be taken for a preferably smaller size of the second stripping container column, and for the second stripping container being operated at a higher pressure, e.g. typically operated at predetermined reference pressure about atmospheric pressure (1000 hPa) compared to an operational pressure of about 200 hPa for the first stripping container.

Said second stripping unit further comprises a second condenser (8) for condensing said vapour of volatile components at said predetermined reference pressure. This second condenser is preferably prepared by same and/or similar methods and means to those used for said first condenser (4).

A pump (9), here a centrifuge type pump generally available from chemical engineering suppliers, is used to pump said condensate from said phase separator (5) to said second stripping column (7).

A residue of the second stripping column, here an aqueous solution of about 0.4 % by weight of NH ₃ at about 98°C, is circulated (10) to the inlet of the first stripping column and there admixed to the inlet liquid.

Examples

The present invention makes it possible to control nitrogen levels in a biogas plant, and the invention has opened the biogas market for nitrogen rich biomasses viewed in the prior art as uneconomical or too difficult to process. Biomasses capable of being processed in biogas plants according to the present invention include e.g. manure from egg layers and broilers. Such biomasses may contain up to 70 % dry matter, and they have a biogas potential exceeding that of corn silage by more than 50 %. Nitrogen rich biomasses such as e.g. manures from egg layers and broilers prevent usage of such biomasses in conventional biogas plants due to excessive formation of ammonia gasses inhibitory for anaerobic fermentation and biogas production.

Several years of testing the concept of the present invention in continuous anaerobic digesters have documented that nitrogen rich biomasses, such as e.g. chicken manures, may be used as the only substrate for biogas production when the nitrogen levels are controlled by the present invention.

A full-scale biogas plant operated with 100 % chicken litter, and having a power production capacity of 3 MW, is currently being built in Northern Ireland. Several other similar projects are in the pipeline. Working example of annual mass and energy balance for a 3 MW biogas plant

Exclusive usage of nitrogen rich biomasses, such as e.g. chicken manures, is made possible by preventing formation of inhibitory amounts of ammonia gasses in the anaerobic digester.

Ammonia inhibition is prevented by stripping ammonium from effluent liquid streams downstream of the anaerobic digester, and by circulating ammonia stripped liquids back to the anaerobic digester.

Continued re-circulation to an anaerobic digester of ammonia stripped liquids, and continued mixing in the anaerobic digester of said liquids with nitrogen rich biomasses, such as e.g. manures from egg layers and broilers, allow biogas fermentation to proceed without ammonia inhibition. Fermented biomass is separated into solid digestate and effluent liquid streams to be re-circulated to the anaerobic digester following stripping of the ammonia present therein. Ammonium stripped from effluent liquid streams downstream of the anaerobic digester prior to re-circularization to the anaerobic digester is collected as ammonium sulfate.

The ammonium stripped, effluent liquid streams are recycled to the anaerobic digester as a substitute for external liquid sources. In the prior art, it would have been necessary to add such external liquid sources to the anaerobic digester in higher amounts without re-circularization of the stripped digester liquids.

Accordingly, the present invention does not only allow nitrogen rich biomasses to be used as the only substrate for biogas production, the present invention also provides a significant improvement in water economy as a result of biomass suspension using only limited amounts of external water sources.

It is clear that the present invention offers a number of advantages over the prior art, including:

- No dependence on mixed biomass inputs;

- An ability to use substantial amounts of poultry manure in the biogas plant;

- Minimization of the effluent disposal water dilution rate; and

Improved nutrient management by production of high value end-products, including concentrated, liquid nitrogen fertilizer, and concentrated, solid phosphorous fertilizer.