Apparatus and method for the efficient utilization of biomass by anaerobic fermentation

Abstract

A device (500) for modifying the fermentation medium (91) in an anaerobic fer-mentation bioreactor (10), comprises a filtration unit (100) being able to be operatively coupled to an anaerobic fermentation bioreactor (10) in such a way that it can receive liquid fermentation medium (91) from the anaerobic fermentation bioreactor (10) and return liquid modified fermentation medium (92) to said anaerobic fermentation bioreactor (10), and comprising one or more filter stages (101, 102, 102', 103, 103') that are configured to remove particles from the retrieved fermentation medium (91) to form a filtered fermentation medium (93); and a first ion separation unit (200) configured to receive a first input stream (201) of filtered fermentation medium (93) and to produce a first output stream (203) of aqueous solution with decreased content of ions in comparison to the filtered fermentation medium (93) and a second output stream (204) with increased content of ions in comparison to the filtered fermentation medium (93). The filtration unit (100) and the first ion separation unit (200) are operatively connected in such a way that filtered fermentation medium (93) can be conveyed (106) from the filtration unit (100) to the first ion separation unit (200) and can be used as the first input stream (201) of the first ion separation unit (200); that the first output stream (203) of the first ion separation unit (200) can be conveyed (107) as modified fermentation medium (92) to the filtration unit (100); and that the second output stream (204) of the first ion separation unit (200) forms an aqueous solution (81, 8T) that has an increased content of ions in comparison to the filtered fermentation medium (93).

Description

[0001] APPARATUS AND METHOD FOR THE EFFICIENT UTILIZATION OF BIOMASS BY

[0002] ANAEROBIC FERMENTATION

[0003] Cross-reference

[0004] The present patent application claims the priority of Swiss patent application No. CH000522 / 2023 of 16 May 2023, which is hereby incorporated by reference in its entirety.

[0005] Field of the invention

[0006] The invention relates to apparatuses and processes for the efficient utilization of biomass by anaerobic fermentation for the production of gaseous fuel, fertilizer and solid fuel.

[0007] Background of the invention

[0008] Plant biomass (called biomass in the context of this description) presents a valuable source for the production of carbon dioxide neutral electricity, heat and fuels. For Germany alone a theoretical potential of more than 94 Mio. t (dry weight) biomass is estimated for 2020 [Ref-01],

[0009] Utilization of plant biomass can be achieved by anaerobic fermentation of the biomass, thereby producing biogas (methane and other components). Methane as a chemical energy carrier can then subsequently be used as a gaseous fuel for various purposes, including the production of electricity. Biogas can be produced from biodegradable material such as e.g. biodegradable municipal waste, waste plant material, animal waste such as manure, sewage, paper waste, food waste etc. It may, however, also be produced from biomass produced particularly for this purpose. While utilization of biomass is partially restrained by environmental issues like the conservation of humus (the organic matter in the ground) and the protection of natural habitats, there is also a lack of economically viable and efficient technologies, which greatly hinders a mobilization of a major part of this potential.

[0010] On one hand, biomass is highly inhomogeneous and comprises a complex mixture of various compounds, such as cellulose, sugars, proteins and fats, which contain a variety of elements in differing amounts. The main constituents of all organic matter are carbon (C), oxygen (O) and hydrogen (H), as well as considerably smaller amounts of nitrogen (N) and sulfur (S), present mainly in amino acids. In addition, plants comprise other elements such as potassium (K), calcium (Ca), magnesium (Mg), phosphorus (P) and chlorine (Cl). Their specific concentrations (g per kg dry weight) greatly vary between different species (e.g., wheat straw contains up to 15 g potassium per kg dry mass compared to 35 g / kg dry mass for normal grass vegetation). This high degree of inhomogeneity, both in constituent elements and their concentration, makes it difficult to find a single process applicable to all kinds of biomass.

[0011] On the other hand, most biomass, especially from plants that can be grown quickly (such as e.g. giant miscanthus, Miscanthus sinensis x Miscanthus sacchariflorus) has a relatively small energy density, which makes its transport over large distances expensive and remarkably reduces its carbon dioxide neutrality. Therefore, a decentralized infrastructure is necessary for its efficient and economical utilization. As a result, the complexity as well as the capital and operational costs of possible processes are greatly limited. This eliminates processes working with high pressure and exceedingly high temperatures, since they require expensive apparatuses and a lot of maintenance.

[0012] Due to these difficulties, the currently used methods for the production of energy and fuel from biomass suffer from a substantial number of problems.

[0013] On one hand, thermal processes (combustion, gasification), convert the nitrogen and sulfur contained within its fuel into nitroxides (NOX) as well as sulfuric oxides (SOX), which are major air pollutants. While this is the case for any kind of fuel, wood contains very little of these two elements (0.03 - 0.1 %w / w dry mass N and 0.01 - 0.05 %w / w dry mass S, in contrast to 1-5 %w / w dry mass N and 0.2 - 0.5 %w / w dry mass S in grass vegetation). However, almost all other kinds of biomass contain much more of these two elements, therefore necessitating extensive cleaning of the exhaust gas, which reduces the profitability of the entire process.

[0014] Furthermore, the high amounts of both potassium and chlorine cause major problems (again wood being an exception). Many potassium compounds possess a melting temperature below 800 °C, which means that ashes with high potassium content start melting during combustion, leading to slag buildup and potential failure of the ash removal system. Additionally, both potassium and chlorine lead to corrosion on parts which are in contact with the exhaust gas (such as heat exchanger and pipes), increased particle emissions via formation of KCI and KSO4 as well as HCI-emissions [Ref-02],

[0015] Biogas is produced by anaerobic organisms such as methanogens and sulfur-reducing bacteria, in a multi-step fermentation process called anaerobic digestion or anaerobic fermentation. A short overview of the involved processes is provided in WO 2019 / 166694 A1 (cf. Figure 1).

[0016] Biogas primarily consists of methane CH4 and carbon dioxide CO2. It may also comprise further compounds in lower quantities such as hydrogen sulfide H2S, water vapor H2O, hydrogen H2, ammonia NH3, nitrogen N2 and oxygen O2.

[0017] In an industrial setup, biogas can be produced in bioreactors called anaerobic digesters or anaerobic fermenters, in which biodegradable material is processed in an anaerobic environment. Various such installations are known from the state of the art, which are optimized for the characteristics of the type of biomass with which they should operate.

[0018] If wet waste fractions shall be utilized, such as wastewater sludge and animal manure, processing preferably takes place in completely stirred vertical cylindrical tank reactors at a low dry matter content (most often < 10 %w / w). When dryer waste fractions should be processed in this type of completely stirred reactor, the input biomass has to be diluted with a liquid. While it possible to recirculate such liquid back to the reactor; side products of the fermentation process that accumulate in the recirculated liquid that show an inhibiting effect on the fermentation process.

[0019] Reactors that are optimized for drier biomass compositions often use the so-called plugflow principle, in which biomass is fed into a horizontal tank reactor from one end of the reactor, and the processed material is removed from the other end of the reactor. During the fermentation processing, the biomass material passes through the horizontal reactor based on a plug-type flow. Such reactors operated on the plug-flow principle can be operated at higher dry content (e.g. a dry matter content of 10-30 %w / w).

[0020] US 5601720 shows an example of a fermentation installation with passive conveying of the biomass through the horizontal reactor. US 2008 / 0138888 A1 , WO 2015 / 075298 A1, and WO 2019 / 115862 A1 disclose examples of fermentation installations using actuators for conveying of the biomass through the horizontal reactor.

[0021] WO 2019 / 166694 A1 shows a variant of such a fermentation installation with a vertical reactor with separate compartments through which the biomass is conveyed gravitationally.

[0022] In regard to the use biogas as a fuel, for example in internal combustion engines, heating or cooking facilities, or fuel cells, methane is the primary carrier of chemical energy, seconded by hydrogen. Inert compounds such as carbon dioxide decrease the calorific value of the biogas, and thus may be removed in the production process. Impurities such as hydrogen sulfide or ammonia should be removed for avoiding the formation of pollutants such as sulfur oxides (SOX) and nitrogen oxides (NOX) in a subsequent combustion process.

[0023] Anaerobic digestion can be inhibited by certain compounds, by negatively affecting the activity of one or more of the groups of microorganisms responsible for the different steps of organic matter degradation. The degree of inhibition depends on the concentration of the inhibitor compound in the anaerobic digester. Potential inhibitors are e.g. ammonium ions, sulfide ions, and metal ions such as Na, K, Mg, Ca, which form during the degradation of the various organic compounds such as proteins, or a present in the biological material.

[0024] Anaerobic digestion by microorganisms is not as susceptible to moderate concentrations of ions such as K+, Na+, Ca2+, Mg2+, since the microorganisms themselves need them in order to grow and function. K+is highly inhibitory to anaerobic bacteria at concentrations > 12 g / L. However, such levels are practically never achieved with the available substrates. Methanogens are strongly inhibited during these processes by high levels of ammonia [Ref-03], which renders e.g. the utilization of chicken manure and other substrates high in nitrogen very difficult. The utilization of food plants such as potatoes or sugar beets, or of maize silage as biomass for biogas production is in direct competition with food production, which is ethically and politically problematic. Woody plant mass does not have that problem and is also less expensive and more abundant. However, the process of anaerobic digestion is quite inefficient when it comes to lignocellulose rich biomass. The reason for this is the high stability of lignocellulose and the fact that a large part of it, namely the lignin, which makes up between 5-25 %w / w of all biomass, cannot be anaerobically digested at all. This is especially problematic since lignin has a very high energy density of ca. 7.1 kWh / kg, compared to cellulose with 5.2 kWh / kg and xylose (main building block of hemicellulose) with 4.6 kWh / kg.

[0025] As a result, the lignin ends up in the fermentation residues, which are often used as compost fertilizer that can be spread on fields. Up to 20% of the lignin becomes part of the humus, and the rest is digested by aerobic microorganisms.

[0026] While said fermentation residues provide nutrients and organic matter to the ground, they do so in a very inefficient way. The distribution as fertilizer requires a large amount of logistics and infrastructure, which is expensive and consumes a lot of time and fuel, thus posing a great problem especially to farmers in poorer regions. Due to this, the transportation distances have to be chosen as small as possible, which often leads to these residues simply being disposed of on the next-best field. Furthermore, such fermentation residues fertilizer contains has a nutrient concentration, typically only 1 %w / w. As a result, such fertilizer is not very profitable, which also reduces the profitability of biomass based energy production.

[0027] Plastic residues in the biomass pose an additional problem, especially for communal organic waste facilities. These residues need to be carefully and time-consumingly removed by hand, in order for the anaerobic digestate to be used as compost by farmers. However, it is unavoidable that some amount of plastic, especially microplastic, still ends up on the field.

[0028] In academic and industrial research, there are multiple approaches to solving these problems individually. None of them, however, allow for a complete solution to the above- mentioned difficulties. For the combustion processes, a vibrating, water-cooled grate can be used in order to keep the melting ash from sticking to it and thus clogging the ash removal system. Furthermore, some of the exhaust gas is recirculated into the combustion chamber for the purpose of lowering the temperature within [Ref-04], However, grate firing technologies in general suffer from low efficiency [Ref-05] compared to the direct combustion of coal dust used in coal burners, which is even further aggravated by the lower combustion temperature. The addition of a vibrating mechanism and water-cooling also significantly increases the capital and operational cost. Considering that, so far, this technology is only viable for burning relatively “high quality” biomass such as wheat straw and miscan- thus, which contain comparatively little nitrogen, potassium and chloride. Since there is currently no solution to the highly increased corrosion due to the high alkali metals and chloride content, it seems unlikely that combustion processes will be applicable to a wide variety of biomass in the near future. Additionally, it needs to be considered that, even if the nitric and sulfuric oxides are removed from the exhaust stream, these important plant nutrients are lost and can no longer be used as fertilizer.

[0029] When it comes to the fermentation processes, the main focus of the ongoing research effort lies on the increase of digestion efficiency and biogas yield of lignocellulosic biomass via different pretreatments, which can be roughly categorized into four categories.

[0030] Mechanical pretreatment consists of milling, extruding and hammering of the raw biomass in order to decrease the average particle size and increase its surface area and thus accessibility by microorganisms. This boosts the biological degradation and biogas production. At the same time, however, these methods consume a lot of energy and only lead to a very small net positive energy generation. Therefore, considering the interest rate, maintenance and write-off, the additional investment in usually not profitable [Ref- 06],

[0031] In hydrothermal pretreatment, the raw biomass is mixed with water and put into a pressure vessel, where it is heated to 140-180 °C for 10-120 minutes. Afterwards, the pressure is suddenly released, thus leading to a “steam explosion”, which further opens up the biomass structure, increasing its biological accessibility. While this process does not require a lot of electricity, it does consume a lot of heat which does get expensive if there is not enough inexpensive waste heat from the biogas electrification. Furthermore, it requires a lot of expensive infrastructure and is difficult to automate [Ref-07], Chemical pretreatment [Ref-08] and biological pretreatment [Ref-09] aims at a depolymerization of the biomass fibers, which increases their anaerobic digestibility. This is achieved by treating the biomass with strong acids and bases such as H2SO4, HCI and NaOH (chemical pretreatment), or with white rot fungi, which are even capable of breaking down the lignin with the help of specialized enzymes (biological pretreatment). However, chemical pretreatment involves the use of dangerous chemicals and expensive process infrastructure. The white rot fungi used in biological pretreatment consume a part of the energy contained within the biomass, thus again lowering the overall energy efficiency.

[0032] Besides these biomass pretreatments, recent research also attempts to tackle the problem of ammonia inhibition during the process by removing it. This is attempted via either ammonia stripping [Ref-10] or acid leaching through a membrane [Ref-11], While this increases the gas production, these methods are highly inefficient, because they only manage to remove relatively little ammonia, and require a lot of maintenance. In addition, ammonia stripping suffers from extensive fouling and process instabilities due to pH fluctuations, since ammonium / ammonia acts as a pH buffer, while acid leaching requires storage of dangerous acids. Furthermore, they do not solve any other problems and inefficiencies as described above, therefore making it difficult for the additional investment to become profitable.

[0033] There is a general need for improvement in this field of technology.

[0034] Summary of the Invention

[0035] It is an object of this invention to provide an installation for producing gaseous fuel from biomass by anaerobic digestion that counteracts one or more of the above-mentioned and other problems, and particularly does provide more favorable conditions for the anaerobic digestion processes.

[0036] It is a further object of this invention to provide a device that allows to provide such favorable conditions for the anaerobic digestion processes by modifying the fermentation medium in an anaerobic fermentation bioreactor. According to the present invention, these objects are achieved through the features of the independent claims. In addition, further advantageous embodiments follow from the dependent claims and the description.

[0037] The solution according to the invention can be further improved by various embodiments, each of which is advantageous in itself, and, unless otherwise specified, can be combined with one another as desired. These embodiments and the advantages associated therewith are discussed below.

[0038] A first aspect of the invention concerns a device for modifying the fermentation medium in an anaerobic fermentation bioreactor.

[0039] Such a device according to the invention comprises a filtration unit being able to be operatively coupled to an anaerobic fermentation bioreactor in such a way that it can receive liquid fermentation medium from the anaerobic fermentation bioreactor and return liquid modified fermentation medium to said anaerobic fermentation bioreactor, and comprising one or more filter stages that are configured to remove particles from the retrieved fermentation medium to form a filtered fermentation medium; and a first ion separation unit configured to receive a first input stream of filtered fermentation medium and to produce a first output stream of aqueous solution with decreased content of ions in comparison to the filtered fermentation medium and a second output stream with increased content of ions in comparison to the filtered fermentation medium. The filtration unit and the first ion separation unit are operatively connected in such a way that filtered fermentation medium can be conveyed from the filtration unit to the first ion separation unit and can be used as the first input stream of the first ion separation unit; that the first output stream of the first ion separation unit can be conveyed as modified fermentation medium to the filtration unit; and that the second output stream of the first ion separation unit forms an aqueous solution that has an increased content of ions in comparison to the filtered fermentation medium.

[0040] The anaerobic digestion of the fermentation medium takes place in a fermentation bioreactor. The fermentation substrate to be digested comprises solid components, as well as a liquid fermentation medium, which is essentially an aqueous solution comprising solved organic and inorganic compounds, potentially in combination with amounts of lipophilic compounds such as liquid fatty substances. By removing at least a part of the ions in the fermentation medium, the resulting modified fermentation medium has a decreased concentration of ions. By constantly removing ions from the fermentation medium with a fermentation medium modification device according to the invention, it is thus for example possible to keep the overall concentration of ions such as K+, Na+, Ca2+, Mg2+in the liquid aqueous medium below a certain threshold, where the ions do not have a detrimental physiological effect on the various microbes that are involved in anaerobic digestion. Such more favorable living conditions for the involved microbes allows for a more efficient production of gaseous fuel, i.e. biogas, from biomass, in an anaerobic fermentation bioreactor.

[0041] At the same time, the amount of K+and Cl- ions in the fermentation medium, and thus also the overall fermentation substrate, can be minimized, which leads to a minimal overall content of potassium and chlorine in the resulting fermentation residue. This increases the melting temperature of ashes resulting from combustion of said fermentation residues, and thus simplifies the thermal utilization of the fermentation residues as solid fuel. The corrosive properties of combustion exhaust gases are reduced, as well as the emission of fine particulate matter and HCI. Similarly, compounds comprising sulfur or nitrogen, such as e.g. H2S or NH3, and others, can be continuously removed from the fermentation medium, namely in their ionized form, such as SC2-, HS_and NF . This allows minimizing the emission of nitroxides (NOX) and sulfuric oxides (SOX) in the exhaust gases. As a result, the fermentation residue becomes a more valuable solid fuel.

[0042] By constantly removing ions such as SC2-(which gets metabolized by the involved microbes to sulfide), HS_, S2-, and HCOs-, CCh2-from the fermentation medium, also the content of H2S and CO2 in the biogas can be reduced.

[0043] The aqueous solution with increased content of ions in comparison to the filtered fermentation medium, as it can be produced with a fermentation medium modification device according to the invention, can also be further utilized. In particular, this aqueous solution with higher ion concentration can be used e.g. as a source material for producing liquid or solid fertilizer products.

[0044] Advantageously, in a fermentation medium modification device according to the invention, the first filter stage of the filtration unit is realized as a cross-flow filter. The use of a cross-flow filter allows for an efficient continuous filtration process, in contrast to a dead-end filtration process, since any particulate matter remaining at the filter surface is continuously removed.

[0045] In another advantageous embodiment of a fermentation medium modification device according to the invention, the filtration unit comprises a first filter line and a second filter line that are arranged parallel to each other. The filtration unit is configured such that said two filter lines can be alternatingly switched to a filtrate outlet of the filtration unit and to a backwash inlet of said filtration unit, such that one of the two filter lines is in a filtering mode, in which fermentation medium flows in one direction and is filtered to a filtered fermentation medium, while the other of the two filter lines is in a backwash mode, in which modified fermentation medium flows in a reversed flow direction and cleans the filter line by backwashing.

[0046] Backwashing allows for an efficient cleaning of filter stages for which crossflow filtration is not possible, in particular any filter stage serially arranged downstream of a first filter stage. Since two filter lines are available, the two lines can be regularly switched, as needed, between filtering and backwashing. This allows for a continuous operation of the filtering unit. The modified filtering medium, in addition to being efficiently returned to the bioreactor by flowing backward through the filter stages, and exiting through the first filter stage, also acts as the backwashing agent, conveying all accumulated particulate matter back into the fermentation medium.

[0047] In a further advantageous embodiment of a fermentation medium modification device according to the invention, the first ion separation unit is configured to receive a first input stream of aqueous solution and a second input stream of aqueous solution and to transfer ions from said first input stream to said second input stream, thereby forming a first output stream of aqueous solution with decreased content of ions in comparison to the first input stream and a second output stream with increased content of ions in comparison to the second input stream. The filtration unit and the first ion separation unit are operatively connected in such a way that filtered fermentation medium can be conveyed from the filtration unit to the first ion separation unit and forms the first input stream of the first ion separation unit, and optionally the second input stream of the first ion separation unit. Advantageously, in such a fermentation medium modification device according to the invention the first ion separation unit is realized as an electrodialysis apparatus.

[0048] Electrodialysis allows to transport salt ions from one solution through ion-exchange membranes to another solution under the influence of an applied electric potential difference in an electrodialysis cell. An electrodialysis cell consists of a dilute compartment and a concentrate compartment formed by an anion exchange membrane and a cation exchange membrane placed between two electrodes. Advantageously, multiple electrodialysis cells are arranged to an electrodialysis stack, in which alternatingly arranged anion-exchange membranes and cation-exchange membranes form stacked multiple electrodialysis cells.

[0049] In the context of the given invention, the electrodialysis process is advantageously run in a continuous manner, in which the first input stream continuously flows into the electrodialysis cell stack, where it acts as the dilute, and leaves as the first output stream, while second input stream continuously flows into the electrodialysis cell stack, where it acts as the concentrate, and leaves as the second output stream.

[0050] Electrodialysis is particularly efficient for aqueous solutions with moderate ion concentrations.

[0051] A particularly advantageous embodiment of such a fermentation medium modification device according to the invention comprises a second ion separation unit configured to receive a first input stream of aqueous solution and a second input stream of aqueous solution and to transfer ions from said first input stream to said second input stream, thereby forming a first output stream of aqueous solution with decreased content of ions in comparison to the first input stream and a second output stream with increased content of ions in comparison to the second input stream. The first ion separation unit and the second ion separation unit are operatively connected in such a way that the second output stream of aqueous solution of the first ion separation unit and the first output stream of aqueous solution of the second ion separation unit are mixed and are used as the second input stream of the first ion separation unit and as both the first input stream and the second input stream of the first ion separation unit; and that the second output stream of the second ion separation unit forms an aqueous solution that has an increased content of ions in comparison to the filtered fermentation medium. Advantageously, in such a fermentation medium modification device according to the invention the second ion separation unit is realized as an electrodialysis apparatus, similar as discussed above for the first ion separation unit.

[0052] An even more advantageous embodiment of such a fermentation medium modification device according to the invention comprises an intermediate concentration solution tank, wherein the mixing of the second output stream of the first ion separation unit and the first output stream of the second ion separation unit takes place in said intermediate concentration solution tank.

[0053] Advantageously, in a fermentation medium modification device according to the invention the first ion separation unit and / or the second ion separation unit are realized as an electrodialysis apparatus.

[0054] A further advantageous embodiment of a fermentation medium modification device according to the invention comprises an ammonia stripping apparatus for retrieving ammonia from the second output stream of the first ion separation unit or the second ion separation unit.

[0055] The separation of ammonia allows for an efficient retrieval of valuable ammonia from the aqueous solution with increased ion concentration in comparison to the filtered fermentation medium. The ammonia can then be used otherwise, for example for producing high nitrogen fertilizers such as ammonium nitrate.

[0056] Various technologies are known for stripping ammonia from aqueous solutions, for example by air stripping the volatile ammonia from the aqueous solution after adjusting the pH value above the pKa value of ammonium.

[0057] A second aspect of the invention concerns an installation for producing gaseous fuel from biomass by anaerobic digestion.

[0058] Such an installation according to the invention comprises an anaerobic fermentation bioreactor and a fermentation medium modification device according to the invention. Advantageously, in an installation according to the invention, a first filter stage of the filtration unit has a filter inlet surface, wherein said filter inlet surface is in contact with the interior of the anaerobic fermentation bioreactor.

[0059] More advantageously, in such an installation the anaerobic fermentation bioreactor comprises an agitator that is configured to generate a flow of the fermentation substrate essentially parallel to the filter inlet surface of the first filter stage of the filtration unit.

[0060] Such an embodiment allows to implement cross-flow filtration at the first filter stage, enabling an efficient continuous filtration process, in contrast to a dead-end filtration process, since any particulate matter remaining at the filter surface is continuously removed by the flow generated by the agitator.

[0061] In another embodiment of an installation according to the invention, the anaerobic fermentation bioreactor comprises a perforated floor through which liquid fermentation medium that is part of fermentation substrate in the interior of the anaerobic fermentation bioreactor can be retrieved.

[0062] Such a bioreactor is particularly useful for fermentation substrates with low water content, such as for example in a plug-flow fermenter. Since the content of liquid fermentation medium in the fermentation substrate is low, filtering fermentation medium directly from the fermentation substrate would not be effective. The liquid fermentation medium continuously flowing or dripping through the perforated floor, driven by gravitation, can be collected and used for a subsequent filtration step.

[0063] In such an installation, the filtration unit of the fermentation medium modification device is advantageously configured to receive fermentation medium retrieved through the perforated floor.

[0064] In addition, or alternatively, an installation according to the invention is configured to convey fermentation medium retrieved through the perforated floor and modified by the fermentation medium modification unit back into the anaerobic fermentation bioreactor.

[0065] In particular, the modified fermentation medium, with its decreased ion content, can be conveyed to the top of the bioreactor, where it can for example be dripped or sprayed onto the fermentation substrate in the bioreactor. As a result, there is a continuous flow of fermentation medium vertically through the fermentation substrate. This recirculation levels the composition of the fermentation medium within the bioreactor. As an additional advantage, it also results in a continuous redistribution of the microbe population within the fermentation substrate.

[0066] In a particular advantageous embodiment of such an installation according to the invention, a first filter stage of the filtration unit has a filter inlet surface, wherein said filter inlet surface is in contact with fermentation medium retrieved through the perforated floor.

[0067] Another particular advantageous embodiment of such an installation according to the invention comprises a filtrate tank for the temporary storage of fermentation medium retrieved through the perforated floor.

[0068] More advantageously, in such an installation a first filter stage of the filtration unit has a filter inlet surface, wherein said filter inlet surface is in contact with the interior of the filtrate tank.

[0069] Advantageously, the installation according to the invention comprises an agitator that is configured to generate a flow of the fermentation medium essentially parallel to the filter inlet surface of the first filter stage of the filtration unit.

[0070] An installation according to the invention advantageously comprises a storage for compounds removed from the fermentation medium, for example a storage tank.

[0071] A third aspect of the invention concerns a method for producing gaseous fuel from biomass by anaerobic digestion.

[0072] Such method according to the invention comprises the steps of: providing an anaerobic fermentation bioreactor; providing biomass as fermentation substrate to be anaerobically digested; anaerobically digesting said fermentation substrate in said anaerobic fermentation bioreactor, whereby biogas and fermentation residue are produced; and retrieving the produced biogas as gaseous fuel; wherein the ion content in the fermentation substrate is continuously reduced by removing ions from the fermentation medium. In an advantageous variant of such a method according to the invention, fermentation medium is retrieved from the fermentation substrate; the stream of retrieved fermentation medium is filtered, resulting in a stream of filtered filtration medium, ions are removed from at least a part of the stream of filtered fermentation medium, resulting in a stream of modified fermentation medium that has a decreased content of ions in comparison to the filtered fermentation medium, and a stream of aqueous solution that has an increased content of ions in comparison to the filtered fermentation medium; and the stream of modified fermentation medium is returned into the fermentation substrate.

[0073] In addition, or alternatively, in such a method according to the invention a fermentation medium modification device according to the invention is provided, and the filtering of the fermentation medium and the removal of ions from the filtered fermentation medium is carried out with said fermentation medium modification device.

[0074] A fourth aspect of the invention concerns a method for producing fertilizer.

[0075] In such a method according to the invention, a method for producing gaseous fuel from biomass by anaerobic digestion according to any of claims to is carried out, and the aqueous solution with increased ion content resulting from said fertilizer producing method is utilized to produce liquid fertilizer and / or solid fertilizer.

[0076] A fifth aspect of the invention concerns a method for producing solid fuel.

[0077] In such a method according to the invention, a method for producing gaseous fuel from biomass by anaerobic digestion according to any of claims to is carried out, and the fermentation residue of the anaerobic digestion process is utilized to produce solid fuel.

[0078] Further aspects of the invention concern gaseous fuel produced with a method for producing gaseous fuel from biomass by anaerobic digestion according to the invention, fertilizer produced with a method for producing fertilizer according to the invention, and solid fuel produced with a method for producing solid fuel according to the invention.

[0079] Further aspects of the present invention become evident as this description proceeds. Brief description of the drawings

[0080] In order to facilitate a fuller understanding of the present invention, reference is now made to the appended drawings. These references should not be construed as limiting the present invention but are intended to be exemplary only.

[0081] Figure 1 schematically shows an embodiment of an anaerobic digester installation according to the invention with a fermentation medium modification device according to the invention.

[0082] Figure 2 schematically shows a wet fermentation bioreactor with an embodiment of a fermentation medium modification device according to the invention.

[0083] Figure 3 schematically shows an embodiment of an ion separation unit of fermentation medium modification device according to the invention.

[0084] Figure 4 schematically shows another embodiment of a fermentation medium modification unit according to the invention, with a second ion separation unit.

[0085] Figure 5 schematically shows another embodiment of a wet fermentation bioreactor with a fermentation medium modification unit according to the invention.

[0086] Figure 6 schematically shows an embodiment of a dry fermentation bioreactor with a fermentation medium modification unit according to the invention.

[0087] Figure 7 schematically shows an embodiment of a fermentation medium modification unit according to the invention with an ammonium stripping unit.

[0088] Figure 8 schematically shows another embodiment of a fermentation medium modification unit according to the invention with a second ion separation unit and an ammonium stripping unit. Detailed description of the invention

[0089] The examples provided hereinafter serve an improved illustration of the present invention but are not suited for restricting the invention to the features disclosed herein.

[0090] An advantageous embodiment of an anaerobic digester installation 1 according to the invention is schematically described in Figure 1. The anaerobic digester installation 1 comprises a fermentation bioreactor 10, in which the anaerobic digestion processes with the biomass take place. The fermentation bioreactor 10 is supplied with biomass material 31 to be processed by the biomass supply 30. Said biomass supply 30 can for example be realized with a conveyor that obtains suitably prepared biomass material 31 from a reservoir and conveys it into the fermentation bioreactor 10.

[0091] The fermentation bioreactor 10 can be realized as a completely stirred bioreactor, in which the fermentation medium 11 has only a small dry mass content of biomass. Alternatively the fermentation bioreactor 10 can be realized as a plug-flow fermenter. Fermentation residues 41 are retrieved from the fermentation bioreactor 10 and stored in a fermentation residue storage 40 for later use or disposal. The fermentation process can be carried batchwise or continuously, the latter being advantageous in regard to process stability.

[0092] The fermentation bioreactor 10 is operatively connected to a fermentation medium modification device 500 according to the invention, which modifies the composition of the fermentation medium 11 in such a way that the conditions for the biogas generating microbe population are in a certain, optimal range and the concentration of certain compounds in the fermentation residue is reduced.

[0093] The fermentation medium modification device 500 comprises a filtration unit 100 and an ion separation unit 200. The filtration unit 100 operatively connects the fermentation bioreactor 10 and the ion separation unit 200. Compounds 81 removed from the fermentation medium are stored in a storage 80 for later use or disposal.

[0094] The general process, which runs continuously alongside anaerobic digestion, can be roughly separated into two steps. In a first step, the fermentation medium 91 , namely the aqueous part of the fermentation substrate 11 , comprising of water and the soluble compounds of the substrate (such as potassium, ammonium and chloride ions, as well as proteins, sugars and other organic compounds) is separated from the rest of the substrate in the filtration unit 100. In a second step, the ions are removed from the resulting filtrated substrate medium 93 and are collected in a concentrate 81 , while the rest of the solution forms a modified fermentation module 92 that is recirculated into the fermenter 10. The details of the implementation, in particular the configuration of the filtration unit 100, depend on the concrete setup of the fermentation bioreactor 10.

[0095] A fermentation medium modification device according to the invention can be implemented both with a “wet” fermenter, and with a “dry” fermenter.

[0096] A more detailed embodiment of a fermentation medium modification unit 500 according to the invention, being operatively connected to a fermentation bioreactor 10 with “wet” fermentation substrate is shown in Figure 2, while Figure 3 shows a possible advantageous embodiment of an ion separation unit 200 as it can be used in said fermentation medium modification unit 500.

[0097] A wet fermentation bioreactor 10 comprises an agitator 15 for agitating the fermentation substrate 11 slurry. While present in any type of wet fermenter, the agitator 15 can vary in form, size and arrangement.

[0098] In order to obtain an aqueous solution from the fermentation substrate 11 than can subsequently be fed to the ion separation unit 200, liquid fermentation substrate 11 is sucked through a first filter stage 101 , 10T. In the shown example, the first filter stage 101 , 10T is located inside the fermentation bioreactor 10 and is suitably mounted 110 to the bioreactor wall 12. The mesh size of the first filter stage 101 , 10T can be in the range of approx, a 0.1-1.0 mm, depending on the average particle size and dry matter content in the fermentation substrate 11 . The first filter stage within the fermenter 10 comprises two separate chambers 101 and 10T. Each chamber is connected to a pipe 108, 109 leading out of the fermenter. The geometry and position of the filter 101 , 101 is chosen in such a way that the agitator 15 creates a flow across the surface 111 of the filter 101 , 10T, which mitigates the unwanted formation of a filtration cake. This method is known as “crossflow filtration”, in contrast to the usual “dead end filtration”, and allows for a continuous and stable filtration process.

[0099] Two pairs of second 102, 102' and third 103, 103' filter stages are provided. A first filtration conduit 108 connects a first chamber of the first filter stage 101 a second filter stage 102 with pore size 30-70 pm and a third filter stage 103 with pore size 0.1-2.0 pm. A second filtration conduit 109 connects a second chamber of the first filter stage 101 with another second filter stage 102' and another third filter stage 103'. Similar for the first filter stage, the pore size of the second and third filter stages is advantageously chosen depending on the fermentation substrate’s properties.

[0100] In the operation mode shown in Figure 2, after passing the first filter stage 101 , the resulting filtrate solution is conveyed along the first filtration conduit 108 (indicated by a black arrow) through the second filter stage 102 and the third filter stage 103 and valve 104 toward a filtrate outlet conduit 106 of the filtration unit 100. Simultaneously, aqueous solution with reduced ion concentration is flowing back from a backwash inlet conduit 107 of the filtration unit 100 via valve 104 through the other third filter stage 103' and second filter stage 102' and the second filtration conduit 109 to the second chamber of the first filtration stage 101 , thereby flushing the filtration stages. This cleans the three filter stages (so called “backwashing”) by removing any possible scaling (deposition of barely soluble calcium and magnesium salts) and carrying the previously filtered microorganisms and organic matter back into the fermenter 10.

[0101] A 4 / 2 valve 104 is used to periodically switching the two filter lines 108, 109 to the filtrate outlet conduit and the backwash inlet conduit 107, so that alternatingly one of the two filter lines 108, 109 provides filtered solution that is fed through outlet 106 to the ion separation unit 200, and the other line 109, 108 receives aqueous solution from the ion separation unit 200 through inlet 107 that is then used for backwashing the inactive three filter stages. The necessary pressure differential is produced by a self-priming circulation pump 501 that also conveys the aqueous solution through the ion separation unit 200.

[0102] The stream of filtrate incoming through the filtrate outlet conduit 106 of the filtration unit 100 is split into two parts, which are fed to a first feed line 221 and a second feed line 22 of the ion separation unit 200. A first effluent line 223 of the ion separation unit 200, carrying an output stream of aqueous solution with reduced ion concentration, is connected to the backwash inlet conduit 107 of the filtration unit 100 and is ultimately feed back into the fermentation bioreactor 10. A second effluent line 224 of the ion separation unit 200, carrying an output stream of aqueous solution 81 with increased ion concentration, is connected to a high concentration solution tank 80. A variety of options can be used for the ion separation unit 200, which are well known from water desalination applications, including capacitive deionization [Ref-12], membrane capacitive deionization MCDI, also known as electrochemical demineralization or electrosorption [Ref-13] and electrodialysis [Ref-14], Of these options, electrodialysis is not only the most mature technology, but also offers some other key advantages such as high selectivity towards inorganic ions (Cl-, K+, NH4+etc.) and comparatively high organic fouling resistance. Also, it allows for an ion concentration of more than 200 %o in the concentrate output, thus significantly decreasing the storage volume of the resulting concentrated ion solution 81 , as well as much lower energy requirements for later water evaporation to obtain solid salts that can be used mineral fertilizer. Therefore, this advantageous technology is shown in the following example of an embodiment of an ion separation unit 200.

[0103] A typical electrodialysis setup is shown in Figure 3. An electrodialysis stack 210 comprises multiple, alternatingly arranged first chambers 213 and second chambers 214, which are alternatingly separated by anion exchange membranes 215 and cation exchange membranes 216. Said anion exchange membranes 215 and cation exchange membranes 216 are only permeable by negative ions or positive ions, respectively. The number of layers as well as the dimensions of the stack depend on the amount of ions that need to be separated as well as the tradeoff between energy consumption and membrane cost. A higher membrane area means less electrical resistance and thus a reduced voltage differential that must be provided by the energy-consuming electrodes 226 and 227, but also increases building costs. The outermost chambers 211 , 212 are filled with an electrolyte, usually sodium sulphate, which is circulated by a pump 225. An anode 226 is arranged in the anode chamber 211 , and a cathode 227 is arranged in the cathode chamber 212. Anode 226 and cathode 227 are connected to a voltage source 217, which drives a direct current through the electrodialysis stack 210. As a result, ions from the solution in the first chambers 213 are transported across the membranes 215, 216 into the second chambers 214.

[0104] The first feed line 221 feeds aqueous solution received from the filtration unit 100 to the multiple first chambers 213. After passing said parallel first chambers 213, the aqueous solution is largely depleted of negative and positive ions and is collected in the effluent line 223. Similarly, the second feed line 222 feeds aqueous solution received from the filtration unit 100 to the multiple second chambers 214. After passing said parallel second chambers 214, the ion concentration in the aqueous solution is largely increased. This concentrated solution is collected in the effluent line 224.

[0105] The setup shown in Figures 1 and 2 is particularly advantageous for fermentation substrates that contain a lot of water, since the water within the increased ion concentration stream 81 is not returned to the fermenter 10 but directed from effluent line 224 into a storage tank 80. This lowers the water content in the fermenter 10, which in turn increases organic loading and biogas production.

[0106] Another advantageous embodiment of a fermentation medium modification device 500 is shown in Figure 4. In addition to the first ion separation unit 200, the depicted fermentation medium modification device 500 comprises a second ion separation unit 250, similar to the first ion separation unit 200.

[0107] Filtrate from the filtration unit 100 is feed only to the feed line 221 of the first ion separation unit 200. The corresponding effluent line 223 with the low ion concentration stream leads back to the filtration unit 100, as in the previous examples. The effluent line 224 with high ion concentration solution is connected to an intermediate storage tank 520, whose content serves both as the feed for the other feed line 222 for the first ion separation unit 200, and as the feed for both feed lines 251 , 252 of the second ion separation unit 250. The effluent line 253 with the low ion concentration stream is returned back to the intermediate storage tank 520. The other effluent line 254 of the second ion separation unit 250, carrying an output stream of aqueous solution 81 with highly increased ion concentration, is connected to a high concentration solution tank 80.

[0108] The working voltage of the second ion separation unit 250 is higher than for the first ion separation unit 200, thus achieving a much higher concentration in the secondary concentrate stream in conduit 254 than in the primary concentrate stream in conduit 224.

[0109] Since water is continuously removed from intermediate storage tank 520 toward the storage tank 80, it is connected to a fresh water supply 260 via a 2 / 2 valve (not shown), in order to control the level of the intermediate tank 520.

[0110] This advantageous embodiment of a fermentation medium modification unit 500 according to the invention offers several advantages. For one, it not only allows to independently control the final concentration, but it can also achieve higher concentrations, since the input feed to the secondary ion separation unit 250 is already more concentrated than the filtrate feed 221 to the first ion separation unit 200. Thus, more ions end up in the final concentrate 81. Additionally, the second ion separation unit 250 can be run with optimal parameters to mitigate the fouling of the ion exchange membranes by the organic matter in the filtrate [Ref-15, Ref-16], For example, it could run at lower voltage, higher flow rates, or with a pulsed electric field (PEF) electrodialysis [Ref-17], This leads to increased performance and longer lifetime of the membranes.

[0111] A fermentation medium modification device according to the invention as part of an anaerobic digester installation with a fermentation medium with high water content has been shown in Figure 2. Another such embodiment is shown in Figure 5, where the fermentation bioreactor 10 and the part of the filtration unit 100 within the fermentation bioreactor 10 is shown, with the first filtration stage 101 mounted to the bioreactor wall connected to the first filtration conduit 108 and the second filtration conduit 109. The position of the first filter stage 101 in the wet fermenter has been chosen in such a way that the agitator 15, in this case a paddle agitator with approx. 6-30 rpm, creates a crossflow across the surface of the filter 101 , with the flow direction being normal to the drawing plane. The rest of the filtration unit 100 and the fermentation medium modification device 500 can be realized similar to the filtration unit and the fermentation medium modification device as they have been already discussed for Figures 2 or 4, and will be discussed for Figures 7 or 8, and thus are not shown.

[0112] Figure 6 shows an embodiment of an anaerobic digester installation 1 that can also be used in the context of a fermentation medium with low water content (“dry” fermentation”), for example in a typical plug-flow fermenter. In such a case, in a bioreactor 10 as shown in the figure, an agitator (not shown) would be designed to move the highly viscous or even semi-solid fermentation substrate 11 horizontally along a longitudinal axis perpendicular to the drawing plane. The fermentation process takes place in a continuous manner, fresh fermentation substrate being added at one end and fermentation residue removed at the other end of the bioreactor. Since the water content of the fermentation medium 11 is low, a first filter stage within the bioreactor is less efficient, and a cross-flow along the surface of the first filter stage cannot be achieved.

[0113] A perforated floor 23 is arranged at a lower end of the bioreactor 10, having a mesh size that is sufficiently small to allow the liquid part of the fermentation substrate 11 , namely the fermentation medium 9T, to pass while withholding the solid components of the fermentation substrate. This filtrate I fermentation medium 9T, which has a much higher water content, is then conveyed through filtrate effluent line 27 into a filtrate tank 21. From the filtrate tank 21 , the filtrate / fermentation medium 9T is conveyed through filtrate feed line 25 to a permeate nozzle 22 arranged at an upper end of the bioreactor 10, from which it is spayed or dripped onto the fermentation substrate 11. In the shown embodiment, pumps 24, 26 are used to convey the fermentation medium 9T. However, the filtrate tank 21 can also be arranged above or below the bioreactor 10, such that the fermentation medium 91'can be conveyed along one of the lines 25, 27 by gravitational force only.

[0114] The fermentation medium modification device 500 is shown only partially, and can be realized similar to Figures 2, 4, 7 or 8. The filtration unit 100 is connected to the filtrate tank 21 by a first filtration conduit 108 and a second filtration conduit 109, and comprises a second filter stage 102, 102' and a third filter stage 103, 103', similar to the other embodiments of filtration units in this description. The first filtration stage, however, is omitted, because its function of first filtration stage is functionally replaced by the perforated floor 23. The fermentation medium 9T is directly retrieved from the filtrate tank 21 .

[0115] An additional advantage of such a setup is that the microbes present in the fermentation medium 9T are evenly distributed within the fermentation substrate, since there is a constant flow of liquid withing the fermentation substrate from the top to the bottom of the bioreactor, independent from the conveying agitator.

[0116] Alternatively, the filtration unit 100 can also comprise a first filtration stage, arranged in the filtrate tank 21 , advantageously in combination with a suitable agitator arranged in the filtrate tank 21 for generating a cross-flow along the surface of the first filter stage. Such a setup has the advantage that the perforated floor 23 in the bioreactor 10 can have larger openings than would be possible without a first filter stage.

[0117] A further embodiment of a fermentation medium modification device 500 according to the invention is shown in Figure 7. The fermentation medium modification device 500 is based on the fermentation medium modification device already discussed for Figure 4. For identical parts, reference is therefore made to said discussion.

[0118] The output stream of the effluent line 224 of ion separation unit 200 with increased ion concentration solution is directed to an intermediate tank 530. From this tank 530, solution is conveyed by pump 551 through line 555 to an ammonia stripping tower 550. The output stream of the ammonia stripping tower is then conveyed by pump 552 through line 556 to the high concentration solution tank 80.

[0119] Air stripping is a well-known method for removing volatile compounds from aqueous solutions, such as for example waste water streams [Ref-18, Ref-19, Ref-20], For stripping ammonia from an aqueous solution as resulting from the ion separation unit 200, ammonium ions NH4+present in the aqueous solution are reacted into volatile ammonia NH3. This is achieved by increasing the pH to a range near or above the pKavalue of ammonium of 9.2, e.g. to a pH value of 10.8-11.5, by adding a suitable basic compound such as lime, slaked lime, sodium hydroxide etc. to the intermediate storage tank 530. In the shown embodiment, the necessary amount of lime water is added to the tank 530 via lime solution supply line 540, in order to adjust the pH of the solution to the required range. At this higher pH, the ammonium ions are deprotonated, and ammonia is formed. Gaseous ammonia is then selectively extracted from the aqueous solution by air stripping, while the other ions remain in solution. The gaseous ammonia can then be reclaimed from the air stream as ammonium ions for example by reacting it with a suitable strong acid, e.g. sulfuric acid. The resulting pure ammonia in the ammonia output 558 of the ammonia stripping tower 550 can then be used for the production of nitrogenous fertilizer.

[0120] Economically, this process is very advantageous, since the influent from the tank 530 has a much higher concentration ammonium (> 10 g / L) than it is usually the case in wastewater treatment (< 500 mg / L), thus considerably lowering the energy consumption.

[0121] Instead of a counter stream ammonia stripping tower 500 as in the shown example, other ammonia stripping installations can be used.

[0122] A further advantageous variant of a fermentation medium modification device 500 according to the invention is shown in Figure 8. The fermentation medium modification device 50 comprises two ion separation units 200, 250 in series, similar to Figure 4. The highly concentrated output stream of the second ion separation unit 250 is then directed to intermediate storage tank 530. The ammonia stripping is then carried out similar to the embodiment discussed for Figure 7.

[0123] The present invention is not to be limited in scope by the specific embodiments described herein. Indeed, various modifications of the present invention, in addition to those described herein, will be apparent to those skilled in the art from the foregoing description and accompanying drawings. Thus, such modifications are intended to fall within the scope of the appended claims. Additionally, various references are cited throughout the specification, the disclosures of which are each incorporated herein by reference in their entirety. List of reference numerals

[0124] I anaerobic digester installation

[0125] 10 fermentation bioreactor, fermenter

[0126] I I fermentation substrate

[0127] 12 wall of bioreactor

[0128] 15 agitator

[0129] 17 biogas

[0130] 21 filtrate tank

[0131] 22 permeate nozzle

[0132] 23 perforated fermenter floor

[0133] 24 filtrate feed pump

[0134] 25 filtrate feed line

[0135] 26 filtrate effluent pump

[0136] 27 filtrate effluent line

[0137] 30 biomass supply

[0138] 31 biomass material

[0139] 40 fermentation residue storage

[0140] 41 fermentation residue

[0141] 80 storage for compounds removed from fermentation medium, high concentration solution tank

[0142] 81, 8T solution with ions removed from fermentation medium, solution with increased ion concentration

[0143] 91, 9T fermentation medium

[0144] 92 modified fermentation medium

[0145] 93 filtered fermentation medium

[0146] 94 aqueous solution as input for the second fermentation medium modification device

[0147] 95 solution with decreased ion concentration

[0148] 100 filtration unit

[0149] 101 , 10T first filter stage 0.1 mm - 1 mm (ex 100)

[0150] 102, 102' second filter stage 30 pm - 70 pm (ex 101)

[0151] 103 third filter stage 0.1 pm - 2 pm (ex 102)

[0152] 104 4 / 2 valve

[0153] 106 filtrate outlet conduit of filtration unit

[0154] 107 backwash inlet conduit of filtration unit

[0155] 108 first filtration conduit 109 second filtration conduit

[0156] 110 mounting of first filter stage

[0157] 111 filter inlet surface

[0158] 200 first ion separation unit

[0159] 201 first input stream

[0160] 202 second input stream

[0161] 203 first output stream

[0162] 204 second output stream

[0163] 210 electrodialysis stack

[0164] 211 anode chamber

[0165] 212 cathode chamber

[0166] 213 first chamber

[0167] 214 second chamber

[0168] 215 anion exchange membrane

[0169] 216 cation exchange membrane

[0170] 217 DC voltage source

[0171] 221 first feed line with solution to be diluted

[0172] 222 first feed line with solution to be concentrated

[0173] 223 first effluent line with decreased ion concentration solution

[0174] 224 first effluent line with increased ion concentration solution

[0175] 225 electrolyte circulation pump

[0176] 226 anode

[0177] 227 cathode

[0178] 228 electrolyte circulation line

[0179] 250 second ion separation unit

[0180] 251 second feed line with solution to be diluted

[0181] 252 second feed line with solution to be concentrated

[0182] 253 second effluent line with diluted solution

[0183] 254 second effluent line with concentrated solution

[0184] 260 fresh water supply line

[0185] 261 first input stream

[0186] 262 second input stream

[0187] 263 first output stream

[0188] 264 second output stream

[0189] 500 fermentation medium modification device

[0190] 501 circulation pump 520 intermediate concentration solution tank

[0191] 530 intermediate storage tank

[0192] 540 lime solution supply line for pH adjustment

[0193] 550 ammonia stripping tower

[0194] 551 ammonia stripper feed pump

[0195] 551 ammonia stripper effluent pump

[0196] 555 ammonia stripper feed line

[0197] 556 ammonia stripper output line

[0198] 558 ammonia output

[0199] References

[0200] Ref-01 DBFZ Deutsches Biomasseforschungszentrum gGmbH, DBFZ Resource Database, https: / / datalab.dbfz. de / resdb / ranking?lang=en, obtained on 8 May 2024.

[0201] Ref-02 Thomas Zeng et al., "Beurteilung der thermischen Nutzung von Biomasse- pellets aus Garresten", DBFZ Deutsches Biomasseforschungszentrum ge- meinnutzige GmbH, 27. April 2012.

[0202] Ref-03 H. Wang et al., “Ammonia effect on hydrogenotrophic methanogens and syntrophic acetate-oxidizing bacteria”, FEMS Microbiology Ecology (2015) 91 , fiv130.

[0203] Ref-04 A. Pollex, "stROhgas: Entwicklung eines Verfahrens zur Vergasung von asche- und chlorhaltiger Biomasse am Beispiel Stroh", Deutsches Biomasseforschungszentrum, 2019, pp. 1-61.

[0204] Ref-05 X. Su et al., “Optimizing biomass combustion in a 130 t / h grate boiler: Assessing gas-phase reaction models and primary air distribution strategies”, Appl. Thermal Engin. (2024), 238, 122043.

[0205] Ref-06 M. Victorin et al., “Characterization of Mechanically Pretreated Wheat Straw for Biogas Production”, Bioenerg. Res (2020) 13, 833-844..

[0206] Ref-07 T. Zerback et al., “Hydrothermal Pretreatment of Wheat Straw — Evaluating the Effect of Substrate Disintegration on the Digestibility in Anaerobic Digestion”, Processes (2000), 10, 1048.

[0207] Ref-08 S.D. Kshirsagar et al., “Dilute acid pretreatment of rice straw, structural characterization and optimization of enzymatic hydrolysis conditions by response surface methodology”, RSC Adv., 2015,5, 46525-46533. Ref-09 Y. Deng et al., “Anaerobic co-digestion of rice straw and soybean straw to increase biogas production by pretreatment with trichoderma reesei RUT C30”, Environmental Progress & Sustainable Energy 2017), 37, 1050-1057.

[0208] Ref-10 D. Yellezuome et al., “Mitigation of ammonia inhibition in anaerobic digestion of nitrogen-rich substrates for biogas production by ammonia stripping: A review”, Renewable and Sustainable Energy Reviews (2022), 157, 112043.

[0209] Ref-11 F. Rivera et al., “Enhancement of swine manure anaerobic digestion using membrane-based NH3 extraction”. Bioresource Technology (2022), 362, 127829.

[0210] Ref-12 S. S. Gupta et al., “Capacitive Deionization (GDI): An Alternative Cost-Efficient Desalination Technique”, in: Advances in Water Purification Techniques, Elsevier, 2019, pp. 165-202.

[0211] Ref-13 P. M. Biesheuvel, A. van der Wai, “Membrane capacitive deionization”, J. Membrane Science (2019), 346, 256-262.

[0212] Ref-14 S. Al-Amshawee at al., “Electrodialysis desalination for water and wastewater: A review”, Chem. Engin. J. (2010), 380, 122231.

[0213] Ref-15 M. Akter, J.-S. Park, “Fouling and Mitigation Behavior of Foulants on Ion Exchange Membranes with Surface Property in Reverse Electrodialysis”, Membranes (2023), 13, 106.

[0214] Ref-16 L. Dammak et al., “A Review on Ion-Exchange Membrane Fouling during the Electrodialysis Process in the Food Industry, Part 1 : Types, Effects, Characterization Methods, Fouling Mechanisms and Interactions” Membranes (2021), 11 , 789.

[0215] Ref-17 B. De Jaegher et al., “A model-based analysis of electrodialysis fouling during pulsed electric field operation”, J. Membrane Science (2021), 642, 119975.

[0216] Ref-18 US Environmental Protection Agency, “Wastewater Technology Fact Sheet Ammonia Stripping”, EPA 832-F-00-019, 2000.

[0217] Ref-19 L. Kinidi et al., “Recent Development in Ammonia Stripping Process for Industrial Wastewater Treatment”, Internat. J. Chem. Engin. 2018, 3181087.

[0218] Ref-20 A. Zangeneh et al., “Ammonia removal from municipal wastewater by air stripping process: An experimental study”, South African J Chem. Engin. (2021), 36, 134-141.

Claims

Claims1 . A device (500) for modifying the fermentation medium (91) in an anaerobic fermentation bioreactor (10), comprising a filtration unit (100) being able to be operatively coupled to an anaerobic fermentation bioreactor (10) in such a way that it can receive liquid fermentation medium (91) from the anaerobic fermentation bioreactor (10) and return liquid modified fermentation medium (92) to said anaerobic fermentation bioreactor (10), and comprising one or more filter stages (101 , 102, 102', 103, 103') that are configured to remove particles from the retrieved fermentation medium (91) to form a filtered fermentation medium (93); and a first ion separation unit (200) configured to receive a first input stream (201) of filtered fermentation medium (93) and to produce a first output stream (203) of aqueous solution with decreased content of ions in comparison to the filtered fermentation medium (93) and a second output stream (204) with increased content of ions in comparison to the filtered fermentation medium (93); wherein the filtration unit (100) and the first ion separation unit (200) are operatively connected in such a way that filtered fermentation medium (93) can be conveyed (106) from the filtration unit (100) to the first ion separation unit (200) and can be used as the first input stream (201) of the first ion separation unit (200); that the first output stream (203) of the first ion separation unit (200) can be conveyed (107) as modified fermentation medium (92) to the filtration unit (100); and that the second output stream (204) of the first ion separation unit (200) forms an aqueous solution (81 , 8T) that has an increased content of ions in comparison to the filtered fermentation medium (93).

2. The fermentation medium modification device according to claim 1 , wherein a first filter stage (101) of the filtration unit (100) is realized as a cross-flow filter.

3. The fermentation medium modification device according to claim 1 or 2, wherein the filtration unit (100) comprises a first filter line (101 , 102, 103) and a second filter line (10T, 102', 103') that are arranged parallel to each other, and wherein the filtration unit (100) is configured such that said two filter lines can be alternatingly switched to a filtrate outlet of the filtration unit (100) and to a backwash inlet of said filtration unit (100), such that one of the two filter lines is in a filtering mode, in which fermentation medium (91 , 9T) flows in one direction and is filtered to a filtered fermentation medium (93), while the other of the two filter lines is in a backwash mode, in which modified fermentation medium (92) flows in a reversed flow direction and cleans the filter line by backwashing.

4. The fermentation medium modification device according to any of claims 1 to 3, wherein the first ion separation unit (200) is configured to receive a first input stream (201) of aqueous solution and a second input stream (202) of aqueous solution and to transfer ions from said first input stream to said second input stream, thereby forming a first output stream (203) of aqueous solution with decreased content of ions in comparison to the first input stream (201) and a second output stream (204) with increased content of ions in comparison to the second input stream (202); and wherein the filtration unit (100) and the first ion separation unit (200) are operatively connected in such a way that filtered fermentation medium (93) can be conveyed (106) from the filtration unit (100) to the first ion separation unit (200) and forms the first input stream (201) of the first ion separation unit (200), and optionally the second input stream (202) of the first ion separation unit (200).

5. The fermentation medium modification device according to claim 4, comprising a second ion separation unit (250) configured to receive a first input stream (261) of aqueous solution and a second input stream (262) of aqueous solution and to transfer ions from said first input stream to said second input stream, thereby forming a first output stream (263) of aqueous solution with decreased content of ions in comparison to the first input stream (261) and a second output stream (264) with increased content of ions in comparison to the second input stream (262); wherein the first ion separation unit (200) and the second ion separation unit (250) are operatively connected in such a way that the second output stream (204) of aqueous solution of the first ion separation unit (200) and the first output stream (263) of aqueous solution of the second ion separation unit (250) are mixed and are used as the second input stream (202) of the first ion separation unit (200) and as both the first input stream (261) and the second input stream (262) of the first ion separation unit (200); and that the second output stream (264) of the second ion separation unit (250) forms an aqueous solution (81) that has an increased content of ions in comparison to the filtered fermentation medium (93).

6. The fermentation medium modification device according to claim 5, comprising an intermediate concentration solution tank (520), wherein the mixing of the second output stream (204) of the first ion separation unit (200) and the first output stream (263) of the second ion separation unit (250) takes place in said intermediate concentration solution tank (250).

7. The fermentation medium modification device according to any of claims 4 to 6, wherein the first ion separation unit (200) and / or the second ion separation unit (25) are realized as an electrodialysis apparatus (210, 211 , 212, 213, 214, 225, 226, 227).

8. The fermentation medium modification device according to any of claims 1 to 7, comprising an ammonia stripping apparatus (550, 530, 540) for retrieving ammonia (558) from the second output stream (204, 264) of the first ion separation unit (200) or the second ion separation unit (250).

9. An installation (1) for producing gaseous fuel (17) from biomass (31) by anaerobic digestion, comprising an anaerobic fermentation bioreactor (10) and a fermentation medium modification device (500) according to any of claims 1 to 8.

10. The installation according to claim 9, wherein a first filter stage (101) of the filtration unit (100) has a filter inlet surface (111), and wherein said filter inlet surface (111) is in contact with the interior of the anaerobic fermentation bioreactor (10).

11. The installation according to claim 10, wherein the anaerobic fermentation bioreactor (10) comprises an agitator (15) that is configured to generate a flow of the fermentation substrate (11) essentially parallel to the filter inlet surface (111) of the first filter stage (101 ) of the filtration unit (100) .

12. The installation according to claim 9, wherein the anaerobic fermentation bioreactor (10) comprises a perforated floor (23) through which liquid fermentation medium (9T) that is part of fermentation substrate (11) in the interior of the anaerobic fermentation bioreactor can be retrieved.

13. The installation according to claim 12, wherein the filtration unit (100) of the fermentation medium modification device (500) is configured to receive fermentation medium (9T) retrieved through the perforated floor (23).

14. The installation according to claim 12 or 13, wherein the installation (1) is configured to convey fermentation medium (9T) retrieved through the perforated floor (23) and modified by the fermentation medium modification unit (500) back into the anaerobic fermentation bioreactor (10).

15. The installation according to any of claims 12 to 14, wherein a first filter stage (101) of the filtration unit (100) has a filter inlet surface (111), and wherein said filter inlet surface (111) is in contact with fermentation medium (9T) retrieved through the perforated floor (23).

16. The installation according to any of claims 12 to 15, comprising a filtrate tank (21) for the temporary storage of fermentation medium (9T) retrieved through the perforated floor (23).

17. The installation according to claim 16, wherein a first filter stage (101) of the filtration unit (100) has a filter inlet surface (111), and wherein said filter inlet surface (111) is in contact with the interior of the filtrate tank (21).

18. The installation according to claim 15 or 17, wherein the installation comprises an agitator that is configured to generate a flow of the fermentation medium (9T) essentially parallel to the filter inlet surface (111) of the first filter stage (101) of the filtration unit (100).

19. The installation according to any of claims 9 to 20, comprising a storage for compounds (81) removed from the fermentation medium (91), for example a storage tank (80).

20. A method for producing gaseous fuel (17) from biomass (31) by anaerobic digestion, comprising the steps of: providing an anaerobic fermentation bioreactor (10); providing biomass (31) as fermentation substrate (11) to be anaerobically digested; anaerobically digesting said fermentation substrate (11) in said anaerobic fermentation bioreactor (10), whereby biogas (17) and fermentation residue (41) are produced; and retrieving the produced biogas as gaseous fuel (17); wherein the ion content in the fermentation substrate (11) is continuously reduced by removing ions from the fermentation medium (91 , 9T).

21. The method according to claim 20, wherein fermentation medium (91 , 9T) is retrieved from the fermentation substrate (11); the stream of retrieved fermentation medium (91 , 9T) is filtered, resulting in a stream of filtered filtration medium (93), ions are removed from at least a part of the stream of filtered fermentation medium (93), resulting in a stream of modified fermentation medium (92) that has a decreased content of ions in comparison to the filtered fermentation medium (93), and a stream of aqueous solution (81 , 8T) that has an increased content of ions in comparison to the filtered fermentation medium (93); and the stream of modified fermentation medium (92) is returned into the fermentation substrate (11).

22. The method according to claim 20 or 21 , wherein a fermentation medium modification device (500) according to any one of claims 1 to 6 is provided, and the filtering of the fermentation medium (91 , 9T) and the removal of ions from the filtered fermentation medium (93) is carried out with said fermentation medium modification device (500).

23. A method for producing fertilizer, wherein a method for producing gaseous fuel (17) from biomass (31) by anaerobic digestion according to any of claims 20 to 22 is carried out, and the aqueous solution (81) with increased ion content resulting from said fertilizer producing method is utilized to produce liquid fertilizer and / or solid fertilizer.

24. A method for producing solid fuel, wherein a method for producing gaseous fuel (17) from biomass (31) by anaerobic digestion according to any of claims 20 to 22 is carried out, and the fermentation residue (41) of the anaerobic digestion process is utilized to produce solid fuel.

25. Gaseous fuel (17) produced with a method according to any one of claims 20 to 22.

26. Fertilizer produced with a method according to claim 23.

27. Solid fuel produced with a method according to claim 24.

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