Organic fertilizer for biogas plants

Abstract

The present invention relates to the field of renewable energy production and provides means to improve the efficacy of a biogas plant and / or a bio-methanation plant and thus, helps accelerating the production of renewable methane, i.e. bio-methane. The improvement is achieved by extracting hydrogenotrophic and methanogenic archaea from the bio-methanation reactor together with remaining medium or dried to be used as fertilizer to be added to the anaerobic digester for improved methane production.

Description

[0001] ORGANIC FERTILIZER FOR BIOGAS PLANTS

[0002] The present invention relates to the field of renewable energy production and provides means to improve the efficacy of a biogas plant and / or a bio-methanation plant and thus, helps accelerating the production of renewable methane, i.e. bio-methane.

[0003] The economic potential of bio-methane for energy generation has become increasingly relevant in the global market. Bio-methane hence constitutes a sustainable and renewable energy source and already today increasingly substitutes other fossil fuels.

[0004] Today two different industrial approaches address the production of bio-methane.

[0005] Well established are biogas plants, often addresses ad anaerobic digesters (AD), which produce a methane-containing biogas in large fermenters with methanogenic bacteria from e.g. plant materials, faeces, sludges and / or organic waste. The content of bio-methane in biogas is typically around 40%. Thus, to produce bio-methane this biogas is then further processed e.g. by separation and / or enrichment steps.

[0006] An alternative approach for the industrial production of bio-methane is a bioreactor suitable for a bio-methanation process, which produces highly enriched methane as a product gas from e.g. hydrogenotrophic archaea cultures, wherein the archaea transform CO2-containing gases and hydrogen, preferably generated from renewable energy sources, into bio-methane. From this approach the content of bio-methane in the product gas is typically around 90-97%. Thus, the bio-methanation approach can be used as an enrichment step in processing biogas produced in an AD.

[0007] The term “bio-methane” or “bio-methanation” in the context of the present application refers to a process involving biological processes, often addressed as “bio-methanation”, and consequently produce methane by exploiting the metabolism of microbes, often addressed as biocatalysts.

[0008] Bio-methanation process, be it in an AD, i.e. a biogas plant based on anaerobic fermentation with anaerobic microorganism or in a bio-methanation plant based on culturing hydrogenotrophic archaea, depends on the metabolic activity of said microbes, which hereinafter are collectively identified as biocatalysts. The activity of all these microbes can be influences via the culture conditions or the availability of nutrients. As such it is well established that optimized culture condition in the biogas plant or bioreactor, such as preferred pH ranges, preferred temperature ranges and optimized feeding conditions and the provision of suitable amounts of micro- and / or macronutrients such as nitrogen and / or sulfur compounds are essential for a successful production of bio-methane.

[0009] In the context of this description the term “micro- and / or macronutrients” is understood as compounds required in small quantities, such as e.g. metalions selected from Fe, Ni, Co, Mo, Se, Mg and W and compounds needed in larger quantities, such as the various compounds or biologically usable compositions of N, K, P and S respectively.

[0010] Thus, it is doubtlessly accepted and based on laboratory experience that a suitable supply of micro- or macronutrient not only optimizes the culture and growth conditions but also improves the stability and efficacy of the methane production. However, this laboratory knowledge is hardly ever directly transferable to industrial scales. One reason may be that it is inconvenient and expensive to simply refill fresh culture medium into a bioreactor to add the suitable supply of nutrients.

[0011] While this strategy works in a laboratory and seems to be very straight forward, it has not been found cost efficient for industrial scale nor are suitably adapted media available. Nevertheless, solutions regarding the micro- or macronutrient management in bioreactors of industrial plants have been developed and disclosed e.g. in WO 2022243361 Al (“System to recycle water / ammonia”).

[0012] Even more difficult is the provision of suitable amounts of micro- or macronutrients into a biogas plant or an AD, which per definition runs not on a standardized culture medium but uses organic materials of various sources, hereinafter also generally addressed as biomass. Already, the process of analyzing the content of micro- or macronutrients in the starting material is a challenge, as not only the starting material itself is diverse, but also the included methanogenic bacteria and their needs may be divers.

[0013] Additionally, as it is known that most methanogenic bacteria cannot break down fats, protein, carbohydrate (starch, sugar) and cellulose in the starting material, for AD it is essential to provide by fermentation reactions soluble nitrogen compounds, minerals and trace elements to break down the cellular mass of these materials. As a consequence, the process management of an AD is highly complex and needs regular adaptation regarding the composition of the starting / feeding material, together with an elaborate analysis and management of the various micronutrients.

[0014] EP 2802639 Al describes e.g. the need and the advantage of a suitable micronutrient supply in the understanding of the metabolic effects and exploitation of methanogenic organisms in an AD, and further provides a method for monitoring at least one or many micronutrients as well as calculating thereof the micronutrient requirements for maintaining ideal culture and growth conditions for the microorganisms during the methanogenic stage.

[0015] Doubtless it is accepted that a suitable supply of micro- or macronutrient promotes optimizing the culture and growth conditions and thus, the efficacy of the methane production in ADs.

[0016] In summary and with the intention to promote renewable energy projects, there is a serious need for less complex and less expensive methods to provide suitable amounts of the necessary micro- or macronutrients in the bio-methanation processes of industrial plants.

[0017] The object of the present invention is thus to find an improvement for the bio-methanation process increasing the efficacy of anaerobic digestion performance in biogas plants with stabilizing and accelerating effects of the processes, thereby supporting the production of biogases with enriched quantity of methane thereby improving the gas quality from bio- methanation plants and / or AD plants.

[0018] This object is solved by providing a ready -to-use fertilizer according to the present invention. Further advantageous details, aspects and further embodiments of the present invention are represented by the embodiments of the dependent claims.

[0019] The term “fertilizer” in its traditional use refers to a composition comprising micro- or macronutrients or organic substrates in various arrangements, which will improve the metabolic activity of - most typically - plants or in agriculture. In the context of biogas plants, the fully fermented organic material at the end of a biogas production cycle is often reused as fertilizer for agriculture.

[0020] In the context of the present invention the term “fertilizer” is developed and used to improve the metabolism of bacteria and / or archaea in general, or more specific of bacteria for anaerobic digestion, and / or methanogenic bacteria and archaea in bio-methanation processes. The use of the fertilizer according to the invention increase the bio-methane production and consequently, also the CH4 yield in the product gas output.

[0021] The “ready-to-use” fertilizer according to the invention is suitable for a wide variety of microorganism and among others particularly microorganisms involved in an anaerobic digester (AD) and responsible for hydrolysis, acidogenesis, acetogenesis or methanogenesis. Also, the fertilizer is suitable for methanogenic microorganism and / or methanogenic archaea selected from the group of non-hydrogenotrophic archaea, such as Methanosarcina barkeri, Methanosarcina mazei, Methanosarcina thermophila, Methanosaeta concilii, Methanosaeta harundinacea, Methanolobus tindarius, Methanohalophilus mahii, Methanomethylovorans hollandica, and Methanococcoides methylutens.

[0022] The fertilizer of the invention is typically a solution, which comprises an aqueous culture medium and a high content of biomass, wherein the biomass derives from methanogenic archaea, preferably hydrogenotrophic archaea selected from the group of Methanobacterium, Methanobrevibacter, Methanothermobacter, Methanococcus, Methanosarcina, Methanopyrus, Methanocorpusculum, Methanoculleus, Methanospirillum and mixtures thereof.

[0023] In the context of the invention, hydrogenotrophic archaea are preferred - which is not to be understood as a limitation to the present invention but a preference only. Hydrogenotrophic archaea need for their metabolism substantial amounts of hydrogen for promoting the methanation and / or cell expansion.

[0024] As they have a restricted hydrogen-dependent metabolism after being extracted from a bioreactor, which provided suitable culture conditions for said hydrogenotrophic archaea, their metabolism and lifespan is restricted. When deprived from hydrogen the hydrogenotrophic archaea stay a life for up to at least 1, if not 3 months but stop being metabolic active, i.e. they stay fresh and do not start a decay process. At the same time, their need of hydrogen limits the risk that they can escape and establish a contaminating population anywhere.

[0025] The fertilizer of the invention is a solution of an aqueous culture medium with a high content of biomass typically comprising a biomass content of at least 1 mg / ml (corresponding to an OD600 of about 5). For calculating the amount of the protein (dry weight in g / L) in this system the measured value of OD600 is mu Implicated by the factor 0,2657. For example, an OD600=40 corresponds to dry weight (g / L) = 40 * 0,2657 = 10,4 g / L.

[0026] The density can be enriched by depriving the solution from its aqueous culture medium, e.g. by filtration. According to the invention, it is preferred to have in the ready-to-use fertilizer solution a biomass content which correlates to an optical density of OD600 [OD600 (=optical density measured at a wavelength of 600 nm) as indicator for amount of biomass] of at least 40 to 100, and as such corresponds to about 8 to 20 mg / ml biomass rising to even 50 mg / ml biomass (corresponding to an OD600 of 250).

[0027] However, in case the biomass content in the bioreactor is not yet at an OD600 of 40 or even OD600 of 100, any extraction from the bioreactor with an OD less than 40 can be simply concentrated by reducing the water content.

[0028] According to a further embodiment the water content of the ready-to-use fertilizer of the invention can also be reduced to a minimum e.g. less than 40 Vol.%, less than 20 Vol.%, less than 10 Vol.%, or even less than 5 Vol.%. The ready-to-use fertilizer may even be completely dry by reducing the water content fully e.g. by heat drying the biomass containing solution.

[0029] Accordingly, the ready-to-use fertilizer may comprise hydrogenotrophic archaea with a biomass content in a liquid form of at least 2 mg / ml corresponding to an OD600 = 10 (2 g / L) or corresponds alternatively, in a dry form to a dry mass of at least 90 wt%.

[0030] The water-reduced fertilizer may have either a paste-like or even powder-like consistency, which has a substantial reduced weight. Such water reduced ready-to-use fertilizer can also be addressed as fertilizer concentrate.

[0031] While the energy input for reducing the water content in the ready-to-use fertilizer may be seen as disadvantage, the reduced weight of the water-reduced fertilizer is clearly an advantage. Further the water-reduced ready-to use fertilizer can be easily packaged and thus, transportation over longer distances is more efficient. Last not least, the water reduced fertilizer has an additionally prolonged shelf life, typically up to 5 years, as all metabolic activities or decay processes in the biomass have been stopped or at least substantially reduced. The ready-to-use fertilizer according to the invention comprises methanogenic archaea and thus, incorporates or comprises a nutrient composition which is ideal for methanogenic microorganisms in general and more specific methanogenic archaea.

[0032] Speaking of nutrient composition, of particular and exemplary interest is e.g. the ratio of carbon to nickel in the ready-to-use fertilizer. The ratio of carbon to nickel is e.g. of interest because Ni plays an essential role in methanogenesis and is necessary to synthesize the cofactor porphyrynoid F430of methyl co-enzyme M reductase, and thus assisting of boosting acetate utilization for methane production.

[0033] Additionally, the fertilizer of the present invention may comprise ions in form of liquid and / or encapsulated ions selected from the group comprising H+, (NH4+), S2-, (PO43), Mg2+, Co2+ / Co3+, Fe2+ / Fe3+, Ni2+, WO37WO42-, Se2-, MoO42-, K+and mixtures thereof as well as the oxidative stages of the mentioned elements. The group of ions is not restricted to the above-mentioned ions but the above-mentioned ones are preferably comprised in the fertilizer of the invention.

[0034] One main advantage of the herein described fertilizer is the provision of all the relevant nutrients as well as the ratio of nutrients suitable for methanogenic microorganisms in a - so to speak - natural formulation, namely in a form of e.g. hydrated and / or cell-encapsulated ions. The term “cell-encapsulated” describes the fact that the nutrients are not only free in solution but are also incorporated in the cellular structure of the microorganisms that form the fertilizer. As these microorganisms are also methanogenic archaea all necessary nutrients are encapsulated in the individual microorganisms. Thus, all metabolic needs in a lifecycle of methanogenic microorganisms are satisfied supply of the hydrated or encapsulated nutrients from the ready-to-use fertilizer of the invention.

[0035] The typical problem in AD plants, namely that the nutrition conditions are not suitable, is thus solved. Any limitations and poorer conversion rates due to an insufficient or not suitable supply of nutrients can thus be excluded.

[0036] With the ready-to-use fertilizer of the invention also the risk of using too much fertilizer and thereby over-fertilizing culture conditions in an AD plant can be excluded. The hydrated ions or the cell-encapsulated nutrients of the ready-to use fertilizer are always in a suitable concentration for other methanogenic microorganisms, which will use, digest and or metabolise the encapsulated ingredients only if needed and thus, in a retarded but perfectly dosed way. The present invention further provides the method for producing a ready-to-use fertilizer for methanogenic microorganism. Said method comprising the steps of firstly establishing in a bioreactor a stable culture of hydrogenotrophic archaea. These hydrogenotrophic archaea will be cultured in a bioreactor and are provided with suitable culture medium to guarantee metabolic activity. Additionally, a suitable supply of feeding gas will allow stable cell growth and / or cell propagation to increase the biomass in the bioreactor. When the biomass has reached a stabile plateau the extraction phase can be started and regularly repeated. Accordingly, the method of the invention comprises a furtherstep of extracting, once or repetitively, a percentage of the hydrogenotrophic archaea together with some remains of the culture medium from the bioreactor.

[0037] The fertilizer as produced by the method of this application comprises in a liquid an organic composition hydrogenotrophic archaea and optionally further methanogenic microorganisms, which have been growing in the bio-methanation reactor.

[0038] According to one embodiment the method for producing a fertilizer according to the invention is further specified regarding the step of culturing the methanogenic, preferably hydrogenotrophic archaea in a bioreactor undersuitable culture conditions for cell growth phase and / or culture conditions for a biomass producing phase. Such culture conditions are well known to the skilled person and have been summarized previously e.g. by Martin et. al., Archaea, 2013, Vol 13, p2-12 or by Thema et al., Energies, 2019, Vol 12, 1670.

[0039] However, even at culture conditions which are optimized for the methanation stage of such methanogenic or hydrogenotrophic archaea the method of the invention will work and whenever a suitable OD600, typically OD600 is 20 to 55, alternatively 25 to 50, 30 to 45 or 20 to 35, or 35 to 50 is reached in the bioreactor the extraction process of the described method may be started or repetitively repeated.

[0040] According to a further embodiment the method for producing the ready-to-use fertilizer according to this description additionally comprises a step of stabilizing the extracted archaea. For this a stabilizing solution may be added. Such stabilizing solution can be the normally used culture medium, but also a dilution of e.g. conservatives, organic fatty acids or alcohols. By adding such stabilizing solutions, the ready-to-use fertilizer and in particularly the biomass in the fertilizer is stabilized and will not enter self-destructive decay processes. Accordingly, the shelf life of the fertilizer can be prolonged. Additionally, it is an advantage that such stabilized solutions, particularly when stabilized by organic compositions, also have the effectto increase the carbon content of the fertilizer, which leads to an even more potent fertilizer.

[0041] Typical stabilizing solutions are known to the skilled practitioner or may be selected from the group comprising stabilizing liquid such as sugar solutions or salty liquids containing sodium ions, chloride ions or salts of nitrates or salts of ammonia phosphate or other suitable components for a fertilizer.

[0042] According to still a further embodiment the method for producing the ready-to-use fertilizer according to this description additionally comprises a step of stabilizing the extracted hydrogenotrophic archaea by removing the remaining liquids from the extracted methanogens and / or optionally drying the extracted methanogenic archaea. One suitable technology - well known to the practitioner - is the drum drying technique which is particularly suitable for liquids or viscous or paste-like consistencies.

[0043] In the drum-drying process, raw ingredients are dried at relatively low temperatures over rotating, high-capacity drums that produce sheets of drum-dried product. This product can be milled to a finished flake or powder form. Modern drum drying techniques results in dried ingredients which reconstitute immediately and retain most of their original cellular structure and in case of the fertilizer of the present invention its nutritional value.

[0044] One of the main advantages of the herein described ready-to-use fertilizer is its bioavailability in general, but particularly its bioavailability for methanogenic microorganisms and / or archaea. While traditional fertilizers are adapted to improve the growth of plants, the fertilizers of the present invention are adapted to improve the metabolism of methanogens.

[0045] Little is known about the needs of methanogens in the active stage of methane production. Particularly, limited is the knowledge of the ideal composition of micronutrients of methanogenic microorganisms or archaea. Despite this lack of detailed knowledge in the art, the present invention offers an effective solution how to provide ideal nutrient composition for methanogenic microorganism and / or archaea.

[0046] The ready-to-use fertilizer of the present invention being based on methanogenic archaea does provide ideal composition of all essential and suitable nutrients, which such methanogenic microorganisms might need and / or prefer for being metabolically active. Additionally, and even more advantageous, as the nutrients in the ready-to-use fertilizer are not only presented in soluble form but incorporated in the biomass of microorganisms - so-to-speak ‘encapsulated’ in the organelles of a microorganism. This natural packaging or depot solution of the micronutrients is particularly suitable for an enrichment with nutrients for methanogenic microorganisms or archaea, which are believed to have the capacity to digest efficiently other microorganisms or archaea.

[0047] Accordingly, the present invention further provides a method of fertilizing particularly a biogas production unit comprising anaerobic digesters, methanogenic microorganisms and / or archaea. Such a method of fertilizing comprises the steps of adding to an anaerobic fermentation process in a biogas production unit the ready-to-use fertilizer of the present invention.

[0048] Further the method comprises to add an amount of 0.5-10 Vol.-% of the ready-to-use fertilizer in the feedstock, the biogas plant or bio-methanation reactor. According to further embodiments and in case of continuous processes an amount of 0.5 to 10% of the reactor volume is continuously added. Preferred amounts for these embodiments are alternatively also 1 to 3%, 2 to 8%, 3 to 6% 4 to 5%, 3 to 10% 5 to 10% of total inclusion into the reactor and are considered effective.

[0049] As a further embodiment a system for improved bio-methane production is provided. In such system is included

[0050] - a biogas unit producing methane-containing biogas from organic substrates;

[0051] - a bio-methanation reactor, wherein the methane-containing biogas from the biogas unit is enriched with methane in a biocatalyst driven bio-methanation reaction.

[0052] While the product gas, namely the methane-containing gas from the biogas unit is postprocess and thereby enriched with methane in the bio-methanation reactor, the biocatalyst which is the active methanogenic organism in the bioreactor is extracted and prepared as ready-to-use fertilizer for fertilizing the biogas plant, i.e. the anaerobic digester (AD), thereby stabilizing and / or improving the bio-methane production rate from a biogas production unit.

[0053] In this circular process of the system according to the invention, wherein a defined amount of the biocatalyst is regularly extracted from the bio-methanation reactor and is prepared for and / or used as fertilizer in the biogas unit, the valorization of nutrients reuse is optimized. Also, the reuse of water and thus, the avoidance of wastewater together with the need of wastewater treatment is optimized. It is the economic value and particularly the cost saving effects of such optimized circular processes, which makes this ready-to-use fertilizer of the present invention and its use such a valuable solution. The circular process according to the system of the invention is further particularly interesting for reducing the need of hydrogen in the bio-methanation process, without reducing the methane content in the product gas.

[0054] In the AD plant, which is fertilized with the fertilizer of the invention, the biodegrading processes of the organic material, biomass, fibres or waste are accelerated, which leads directly to a better conversion of the gases produced in the AD plant. Such better conversion leads to a biogas with a high methane content, beside the CO2 content in the biogas. If now this methane- enriched biogas is used as a feeding gas for the bio-methanation reactor the needs of H2 to convert the remaining CO2 is lower than with a biogas from a not fertilized AD. Thus, for still producing highest quality methane as product gas in the bio-methanation a reduced amount of hydrogen is needed, which reduced the production costs substantially.

[0055] This circular process leads thus not only to an improvement, but the fertilisation of the AD leads firstly to the enriched gases from the AD plant and the use of such enriched biogas leads to a better conversion rate, effectivity, and a solid cost reduction of the bio-methanation reactor producing high quality bio-methane with a lower input of hydrogen.

[0056] Furthermore, the fertilizer is not only useful to directly fertilise other microbial and / or methanogenic processes, it is additionally also a suitable starting material to produce nourishing media - typically identified as culture media- for microbial and / or methanogenic processes, which is stabilizing and / or improving the growth or production rate of microorganisms.

[0057] In the examples are summarised the results illustrating on the one hand the bio-methanation potential (BMP) of different starting materials, such as deep litter, seed gras or fibres (Figure 6).

[0058] Typically, the starting materials used can be identified by their origine, such as seed grass straw, deep litter and fiber or alternatively by their content of volatile solids (VS).

[0059] Table 1: Mean of dry matter and organic matter in %. Furthermore, Figure 5 illustrates the increase in methane yield expressed in Nm3 / ton VS for these materials, which can be substantially increased by using the fertilizer of the present invention.

[0060] Thus, the economic value and particularly the cost saving effects of such optimized circular processes, which makes this ready-to-use fertilizer of the present invention and its use such a valuable solution, also is shown by improving the carbon intensity of a bio-methanation process.

[0061] Not only increases the ready-to-use fertilizer the metabolic activity of the methanogens, it also increases the amount of carbon reuseable and not wasted, which has a substantially positive effect on the carbon intensity of an industrial process.

[0062] In the context of renewable energies, carbon bound in biomass is a renewable but limited source and thus, a valuable compound. The fertilizer of the present invention is thus also a storage for carbon, which can be reused on demand. Additionally, the carbon bound in biomass is easier to use, and has a much better bioavailability compared to carbon- containing gases.

[0063] BRIEF DESCRIPTION OF THE DRAWINGS

[0064] The present invention is further explained in the following description for clarifying the correlation of the claimed examples as shown in the figures.

[0065] Figure: 1 shows a conventional anaerobic digestion plant (AD) from which the biogas, a carbon dioxide and methane containing gas mixture is transported and fed into a bio-methanation reactor (102) that is enriched with suitable nutrients (101) and H2 stemming from an electrolyser plant (104). In the bio-methanation reactor due to a bio-methanation reaction of a suitable biocatalyst the biogas is enriched with methane leading to a product gas with up to 97% methane. Conventionally, the metabolic water, which is one further reaction product of the bio-methanation reaction is extracted and guided to a wastewater treatment plant (103).

[0066] Figure: 2 schematically shows the circular process of the present invention wherein the anaerobic digestion plant (AD) that is enriched with the fertilizer of the invention, containing by the biocatalyst including the nutrients stemming from a bio-methanation reactor (202). The AD plant provides in this circular process the biogas with still a high contend of carbon dioxide to the bio-methanation reactor. Further in this circular process the bio-methanation reactor is fed by the CO2 containing biogas of the AD and additionally with suitable nutrients (201). Together with the H2 from the electrolyser (203) and the catalyst in the bio-methanation reactor the methane content in the product gas is increased.

[0067] Figure: 3 schematically shows the process of the present invention wherein the biocatalyst, i.e. the fertilizer, includingthe nutrients coming out of the bio-methanation reactor is further concentrated or dried (e.g. with the use of an evaporator) and afterwards distributed to other anaerobic digestion plants or a bio-methanation plant. The fertilizer is produced as already described in Figure 1 and 2.

[0068] Figure: 4 presents the results of the testing for the optimised amount of ready-to-use fertiliser (extracted biocatalyst) in comparison to the control BMP using Glucose as an ideal substrate (301). Tested are three different concentrations of the liquid fertilizer (extracted biocatalyst from the bio-methanation plant) regarding the CH4 yield measured in Nm3 / ton VS.

[0069] Concentration #1 = 0,6 g VS of substrate and 18,5 gVS of inoculum (liquid fertilizer “Bioliquid”)) (303), Concentration #2 = 0,3 g VS of substrate and 19,5 g VS of inoculum (liquid fertilizer “Bioliquid”)) (302), Concentration #3 = 0,15 g VS of substrate and 20,0 g VS of inoculum (liquid fertilizer “Bioliquid”)) (304).

[0070] The methane production yield during the test period in days is shown in Nm3 / ton VS and clearly it was established that concentration 3 showed over a period of 30 days the best BMP and was even better than the positive Control (301) based on glucose and as such an ideal starting material.

[0071] Figure: 5 illustrates the BMP results of using Concentration 3 of liquid fertilizer “Bioliquid”, which was identified as optimised amount, on different starting materials, namely as positive Control was used glucose (401), seed grass straw (402), deep litter (403) and fiber (404). The methane production yield duringthe testing period in days is expressed as methane yield in Nm3 / ton VS.

[0072] VS stands for “volatile solids” and thus, the fraction that can be converted into methane.

[0073] Figure: 6 illustrates the BMP of the different starting materials without any liquid fertilizer “Bioliquid”, namely as positive Control glucose (diamonds), seed grass straw (squares), deep litter (triangles) and fiber (cross). The methane production yield during the testing period in days is expressed as methane yield in Nm3 / ton VS.

[0074] Figure 7 shows the accumulated bio-methane potential (BMP) for the substrate fiber without fertiliser (squares) and fiber plus liquid fertilizer according to the invention (dots). The methane production yield duringthe testing period in days is expressed as methane yield in Nm3 / ton VS and shows 29% improved yield.

[0075] Figure: 8 shows the accumulated methane potential for the substrate seed grass without fertiliser (squares), seed grass with liquid fertilizer having volatile solids of 1,5% (triangles), and seed grass with dried fertilizer of 9,1% biomass. The methane production yield duringthe testing period in days is expressed as methane yield in Nm3 / ton VS and shows 5% improved yield when using the liquid fertiliser corresponding to 1,5% biomass and 17% improved yield when using the fertiliser corresponding to 9,1% biomass.

[0076] Examples:

[0077] Example 1: State of the art

[0078] According to one example, as schematically shown in a conventional anaerobic digestion (AD) plant and a bio-methanation reactor (102) typically exchange methane containing gas in an unidirectional way only. Both plants are conventionally connected to enrich in the bio- methanation unit the biogas containing still substantial amounts of CO2 which are produced in the AD plant. For this enrichment step nutrients and hydrogen gas is fed to the bio-methanation unit for a Rowing the bio-methanation reaction performed by suitable biocatalysts. The H2 gas is produced and supplied by an external electrolyser plant (104). The product gas containing methane is collected and guided to storage or to the gas grid. The metabolic water produced in the bio-methanation diluting the culture conditions of the bio-methanation unit is extracted with or without containing amounts of the biocatalyst and guided to a wastewater treatment (WWT) plant (103).

[0079] Example 2:

[0080] To improve the efficiency of the afore-mentioned installation the invention firstly extracts and collects the biomass - with or without culture medium- from the bio-methanation reaction and reuses the biomass as fertilizer in the AD plant, from which the biogas is collected as a feeding gas for the bio-methanation reactor.

[0081] Figure 2 shows this circular process wherein the AD plant is enriched with nutrients by adding fertiliser according to the invention directly via a supply line or by a feeding scheme. For this the fertilizer is produced by extracting the biomass from the bio-methanation reactor or vessel (202) and to deliver and / or pump the liquid fertilizer containing all the nutrients, micronutrients and macronutrients to the AD plant.

[0082] The liquid Fertilizer then enriches the feedstock in the AD plant and supports the microorganisms which are degrading and fermenting the biomass or waste into bio-methane and biogases. Due to an ideal and thus more than appropriate amount of nutrients, micronutrients and macronutrients for the microorganism in the biogas plant, the turnover in the AD plant is accelerated and the retention times in the AD plant substantially reduced, while at the same time the microorganisms effect a higher conversion rate to form bio-methane, CO2 and biogases.

[0083] Further as shows in Figure 2, the improved, meaning methane-richer gases obtained in the fertilized AD plant are then to be used to feed the bio-methanation unit. Due to the already methane-enriched biogas fed into the bio-methanation reactor a lower amount of H2 from the electrolyser is required for total turnover of the remaining CO2 while still obtaining an essentially pure or at least 94-99% methane-containing gas.

[0084] As the activity of the electrolyser is the most cost intensive step in this circular process, these savings in H2 lead to a substantial reduction in production cost, while still obtaining the highest quality of product gas.

[0085] The present invention not only allows to provide cleaner and higher yields of bio-methane, but at the same time saves production costs as lower amounts of hydrogen are needed for the same gas quality.

[0086] Example 3:

[0087] Tests were performed measuring the BMP of substrate plus different concentration of fertiliser added to the substrate. The tests were performed to identify an ideal amount of f ready-to-use fertiliser (extracted biocatalyst) added to the substrate, here fiber. The BMP was measured in comparison to a positive control using Glucose as substrate (301). Tested are three different concentrations of the liquid fertilizer (extracted biocatalyst from the bio-methanation plant

[0088] Concentration #1 = 0,6 g VS of substrate and 18,5 gVS of inoculum (liquid fertilizer “Bioliquid”)) (Fig. 4: 303),

[0089] Concentration #2 = 0,3 gVS of substrate and 19,5 g VS of inoculum (liquid fertilizer “Bioliquid”)) (Fig. 4: 302),

[0090] Concentration #3 = 0,15 g VS of substrate and 20,0 g VS of inoculum (liquid fertilizer “Bioliquid”)) (Fig. 4: 304).

[0091] The methane production yield during the test period in days is shown in Nm3 / tonVS and clearly it was established that Concentration #3 over a period of 30 days showed the best BMP and was even better than the positive Control (301) based on glucose.

[0092] Example 4:

[0093] In a batch test (IL reactor) three different substrates were tested by adding the fertilizer according to the invention and according to Concentration #3 to deep litter, seed grass straw and fiber.

[0094] Figure 8 shows the three biomasses that were used in this Example. The Example will illustrate the potential of the three biomasses and will analyze if the fertilizer has an impact on the methane production during decay in the chosen biomasses.

[0095] The test was carried out in BPC Instruments’ AM PTS® II with added slurry from Rybjerg Biogas. The slurry used in the test was from the reactor tank. The test was started 5 days after sampling of the slurry. The biomasses were sampled at Rybjerg Biogas plant and were also used 5 days after sampling.

[0096] Methane production was logged during the test period by a temperature at 52°C and the test period was 37 days. Before starting the test, the VFA and pH was analyzed to check that the inoculum was in good condition. The potential of methane production has been determined using Bioprocess Control equipment (Measurement protocol for biogas potential, Measurements for verification tests (ETV, CBMI), v6, 16 / 5-2011). For adding the correct amount of liquid fertilizer, it is possible to use:

[0097] Biocatalyst liquid, Concentration #3: 0,15 g VS of biocatalyst liquid added (10 grams)

[0098] Liquid fraction, Concentration #3: 0,04 g VS of liquid fraction added (10 grams) Concentrated biomass, Concentration #3: 1,0 g VS of concentrated biomass added (12 grams)

[0099] Example 5:

[0100] Figure 7 shows the accumulated methane potential comparing the use of only the Fiber substrate (squares) and Fiber together with the liquid fertilizer (dots). Methane production yield during the test period in days is shown in Nm3 / ton VS. We showed that the mixed fiber plus liquid fertilizer can increase the yield of methane produced by 29% compared to methane produced per ton of VS (volatile solids) using fiber substrate alone. Thus, increasing the utilization rate of the original substrate substantially.

[0101] Additionally, Figure 8 shows the accumulated methane potential for the Seed grass substrate alone (squares) compared to Seed grass and liquid fertilizer 1,5% biomass (triangles), and seed grass and fertilizer with 9,1% biomass.

[0102] Methane production yield du ring the test period in days is shown in Nm3 / tonVS. We showed that the seed grass mixed with liquid fertilizer produced more methane per ton of VS, namely 5% more when a dry mass of 1,5% fertilizer was used and 17% more, when a dry mass of 9.1% fertilizer was used, respectively. Thereby, showing substantial benefit of increasing the nutrients load inside an anaerobic digestorfor methane yield.

Claims

Claims1. Method for producing a fertilizer for microorganism and / or methanogenic microorganism used for the bio-methanation in an anaerobic digester or bio- methanation plant comprising the steps:- establishing in a bioreactor a culture of hydrogenotrophic archaea,- culturing the hydrogenotrophic archaea in a bioreactor and- extracting of the hydrogenotrophic archaea togetherwith remains of the culture medium from the bioreactor.

2. Method for producing a fertilizer accordingto claim 1, wherein the step of culturingthe hydrogenotrophic archaea in a bioreactor comprises culture conditions for a biomass producing cell growth phase and / or culture conditions for a methane producing phase, and optionally reaches a biomass index of OD600= 10 to 160, or Dry mass (DM) content of about 2g / l to 40g / L .

3. Method for producing a fertilizer accordingto claim 1 or 2, additionally comprising the step of stabilizing the extracted hydrogenotrophic archaea by adding suitable amounts of culture medium, by diluting with or by storing in a stabilizing liquid.

4. Method for producing a fertilizer accordingto claim 3, wherein the stabilizing liquid is selected from the group comprising of compounds complexing in a biologically usable way the Ni, Co and / or Fe or other supplements of organic origin.

5. Method for producing a fertilizer accordingto claim 1 or 4, additionally comprising the step of stabilizing the extracted hydrogenotrophic archaea by removing the remaining liquid from the extracted hydrogenotrophic archaea and optionally drying the extracted hydrogenotrophic archaea.

6. A “ready-to-use” fertilizer comprising hydrogenotrophic archaea with a biomass content in a liquid form of at least 2 mg / ml corresponding to an OD 10 or in a dry form to a dry mass of at least 90 wt%.

7. The fertilizer according to claim 6, wherein the microorganism to be fertilized are selected from the group comprising communities found in anaerobic digesters, methanogenic microorganisms, archaea, and methanogenic archaea.

8. The fertilizer according to any one of the claims 6 or 7, wherein the methanogenic microorganisms are selected from the group comprising of Methanobacterium, Methanobrevibacter, Methanothermobacter, Methanococcus, Methanosarcina, Methanopyrus, Methanocorpusculum, Methanoculleus, Methanospirillum and mixtures thereof.

9. Method of fertilizing a biogas production unit comprising the steps of:- adding to an anaerobic fermentation process in a biogas production unit the fertilizer according to claim 6 to 8.

10. Method of fertilizing a biogas production unit accordingto claim 9, the method comprises the addition of an amount of 0.5-10 Vol.-% of the ready-to-use fertilizer in the feedstock, or in a continuous process to continuously include of the ready-to-use fertilizer an amount equal to 0.5 to 10% of the reactor volume.

11. Method according to claims 1-5 or fertilizer according to claims 6-8, wherein the hydrogenotrophic archaea are selected from the group comprising of Methanobacterium, Methanobrevibacter, Methanothermobacter, Methanococcus, Methanosarcina, Methanopyrus, methanocorpusculum, methanoculleus, and methanospirillum or mixtures thereof.

12. System for improved bio-methane production comprising:- a biogas unit producing methane-containing biogas from organic substrates;- a bio-methanation reactor, wherein the methane-containing biogas from the biogas unit is enriched with methane in a biocatalyst driven bio-methanation reaction; and wherein a defined amount of the biocatalyst is regularly extracted from the bio- methanation reactor and is prepared for and / or used as fertilizer in the biogas unit.

13. Use of the fertilizer according to claims 6 to 8 for fertilizing microorganisms or methanogenic microorganisms according to claims 9 and 10 or for stabilizing and / or improvingthe production rate of the microorganisms.

14. Use according to claim 13 for stabilizing and improvingthe methane production rate from a biogas production unit or a bio-methanation unit.

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