DE102014001476B4 - Electrobiogas plant with exoenzyme farm - Google Patents

Abstract

Apparatus for producing biogas and for generating electrical energy, containing
a biogas digester,
an anode, the anode
attached to the inside of the biogas digester,
during operation of the biogas fermenter is at least partially in contact with the located in the biogas digester biomass, and
is colonizable with exoelektrogenen bacteria, a cathode, wherein the cathode
attached to the outside of the biogas digester,
is electrically connected to the anode, and
is separated from the anode by an ion permeable separator, and
an exoenzyme farm, the exoenzyme farm
is arranged outside the biogas digester,
can be fed with biomass, and
biomass in the exoenzyme farm is colonized with aerobically living microorganisms,
and wherein in the Exoenzymfarm produced by the aerobically living microorganisms enzymes from the Exoenzymfarm via a line in the biogas fermenter can be introduced.

Description

The present invention relates to a device for producing biogas and for generating electrical energy. The device according to the invention comprises a biogas fermenter in which there is an anode which can be colonized with exoelectrogenic bacteria, a preferably air-breathing cathode in electrical connection with the anode on the outside of the biogas fermenter, and an exoenzyme farm with the aid of which enzymes, in particular cellulases and laccases, prepared and introduced into the biogas fermenter, preferably via the cathode. The device according to the invention is thus a combination of a biogas fermenter and a microbial fuel cell (MFC).

With more than 7,000 biogas plants installed in Germany and an annual electricity production of up to 17.5 billion kWh, biogas is the most important pillar of bioenergy production. With a share of around 30%, biomass energy is the largest share of so-called renewable energies besides wind energy , Biogas also offers the advantages of being able to be produced and stored irrespective of the weather. However, with the amendment of the Renewable Energy Sources Act and within the framework of the so-called "electricity price brake", new plant construction has declined sharply. In order to increase the efficiency of biogas plants and make them more attractive to plant manufacturers, it is necessary to recognize and circumvent limiting factors in biogas production.

In biogas fermenters, methane is produced by a close interaction of different microorganisms from biomass ( 1 ). These are in part sensitive and fault-prone processes, with any disruption that can easily lead to a reduction in methane yield. This partly limits the effectiveness of biogas production considerably.

In the first step of biogas production, hydrolysis, polymeric substrates from biomass such as manure, corn silage or organic waste are digested to form monomers. This is one of the limiting factors of biogas production, since these substrates are usually complex biopolymers that need to be dissected outside the cells before they can be further metabolized. This is done with the help of exoenzymes, which hydrolyze the polymers. This attack is further compounded by the fact that the complex substrates are mostly water-insoluble and / or inert. The formed monomers are then degraded in the next step, acidogenesis, from primary fermenters to lower fatty acids, CO ₂ and H ₂ . So-called secondary fermenters (acetogens) use the products from acidogenesis and produce acetate, CO ₂ and H ₂ during acetogenesis. From these products, in the last step, methanogenesis, methanogenic organisms (methanogens) can produce CH ₄ and CO ₂ .

Hydrogen plays an important role in these processes. Acetogens and methanogens must live in a close, syntrophic community, as the fermenters are only able to produce H ₂ when the hydrogen partial pressure is low enough. If this is not possible because methanogenesis does not proceed fast enough, lower fatty acids are increasingly accumulated in the reactor, resulting in a drop in pH. This in turn inhibits the methanogens and thus reduces the biogas yield. Therefore, it is crucial for a proper fermentation process that the entire biogas production process remains in a stable equilibrium.

In the prior art, work is known in which in bioelectric reactors (BERs) cathodes were used to improve the methane yield. Methane was produced either by H ₂ produced at the cathode or by a direct transfer of electrons from the cathode to the methanogens at the cathode. Partly the methane yield was increased and a lower accumulation of fatty acids was observed. However, these structures required a very low potential at the cathode, which could only be achieved by applying a current from the outside. Thus, energy had to be spent to accelerate methanogenesis.

Further, in the prior art, microbial fuel cells have been externally connected to thermophilic biogas fermentors to increase their stability. However, a stabilization of the pH and / or the processes in the fermenter could not be achieved. In addition, submersible microbial fuel cells have been described for energy production in sewage treatment plants, which was hampered by a too low potential at the cathode. Finally, attempts have been made in the prior art to reduce the CO ₂ concentration in biogas by means of a fuel cell and a bipolar membrane, and thus to increase the methane content in biogas.

In this context, the document describes DE 43 08 921 A1 a method for treating substances or mixtures containing biodegradable substances or their precursors containing an enzymatic hydrolysis step, followed by a chemical-physical hydrolysis step. Next describes the document WO 2012/054629 A2 bio-electrochemical systems for the treatment of water, waste water, gases and other biodegradable substances, comprising an aqueous compartment containing at least one anode and at least one cathode, a gaseous compartment containing at least one cathode, and electrogenic microorganisms in the aqueous compartment. In addition, the document describes US 2013/0299400 A1 bio-electrochemical systems for treating wastewater and acid gas generated by anaerobic microorganisms, comprising an anaerobic reaction chamber having an anode and a cathode, methanogenic microorganisms in the vicinity of said cathode, and a power source. Next describes the document WO 01/56715 A1 a process for the treatment of organic waste, as well as a corresponding waste treatment plant, comprising mechanical and biological treatment steps, wherein the biological treatment includes aerobic hydrolysis. Finally, the document describes US 2009/0142627 A1 a biological current generator containing an anaerobic region containing anaerobic microorganisms, an anode with an electron mediator, an aerobic region containing molecular oxygen and a cathode, and a membrane defining these regions.

In contrast, the present invention has the object to stabilize the processes during biogas production from organic material and to regulate meaningful, so as to allow an increase in efficiency in biogas production. In particular, the polymer degradation is accelerated and process disturbances, such as the increase of the hydrogen partial pressure, the accumulation of fatty acids and the lowering of the pH, are prevented or mitigated. This should be possible without external supply of electrical energy, ideally even with additional generation of electrical energy.

This object is achieved by the embodiments characterized in the claims. In particular, an apparatus for producing biogas and for generating electrical energy is provided according to the invention.

• einen Biogas-Fermenter,
• eine Anode, wobei die Anode an der Innenseite des Biogas-Fermenters angebracht ist, während des Betriebs des Biogas-Fermenters zumindest teilweise in Kontakt mit der in dem Biogas-Fermenter befindlichen Biomasse steht, und mit exoelektrogenen Bakterien besiedelbar ist,
• eine Kathode, wobei die Kathode an der Außenseite des Biogas-Fermenters angebracht ist, elektrisch mit der Anode verbunden ist, und von der Anode durch einen ionendurchlässigen Separator getrennt ist, und
• eine Exoenzymfarm, wobei die Exoenzymfarm außerhalb des Biogas-Fermenters angeordnet ist, mit Biomasse beschickbar ist, und in der Exoenzymfarm befindliche Biomasse mit aerob lebenden Mikroorganismen besiedelt ist, und wobei in der Exoenzymfarm von den aerob lebenden Mikroorganismen produzierte Enzyme von der Exoenzymfarm über eine Leitung in den Biogas-Fermenter einleitbar sind.

Accordingly, an object of the present invention relates to an apparatus for producing biogas and for generating electrical energy containing

• a biogas digester,
• an anode, wherein the anode is attached to the inside of the biogas fermenter, during the operation of the biogas fermenter is at least partially in contact with the biomass located in the biogas fermenter, and is populated with exoelektrogenen bacteria,
• a cathode, wherein the cathode is attached to the outside of the biogas fermenter, is electrically connected to the anode, and is separated from the anode by an ion-permeable separator, and
• an exoenzyme farm where the exoenzyme farm is located outside the biogas digester, biomass feedable, and biomass located in the exozyme farm is populated with aerobic microorganisms, and enzymes produced by the aerobic microorganisms in the exoenzyme farm are supplied via a conduit to the exoenzyme farm can be introduced into the biogas fermenter.

The term "biogas digester" is not particularly limited in the context of the apparatus of the present invention. It includes any known in the art biogas fermenter, in particular any devices in which biomass can be converted by means of microorganisms to CH ₄ and CO ₂ . The terms "biogas fermenter", "fermenter", and "biogas plant" are used synonymously in the present application.

The anode attached to the inside of the biogas fermenter is not particularly limited in material and shape, provided that it is colonizable by exoelectrogenic bacteria and is stable enough not to be damaged by the solid components of the substrate. Prefers For example, the anode is made of carbon materials such as graphite cloth, carbon fiber woven fabric, or carbon nanotubes, or steel or titanium. The colonization of the anode with exoelektrogenen bacteria takes place either spontaneously during operation of the device according to the invention by existing in the biogas fermenter biomass existing natural populations of such bacteria, or by a pre-incubation of the anode with such bacteria.

Exoelectrogenic bacteria are known in the art. Preferred are the exoelektrogenen bacteria which colonize the anode of the device according to the invention, members of the genus Geobacter, for example Geobacter sulfurreducens, or members of the genus Shewanella, for example Shewanella oneidensis.

The attached to the outside of the biogas fermenter cathode is subject in material and shape no particular restrictions. It also preferably consists of carbon materials, such as graphite fabric, activated carbon fabric, or carbon nanotubes, or of steel or titanium. In a preferred embodiment, the cathode is an air breathing cathode.

The phrase "electrically connected to the anode" includes the presence of an electrical load between the anode and the cathode, i. the anode and cathode are not shorted. About the resistance of the electrical load, the anode and cathode potential can be adjusted. In a preferred embodiment, the anode is connected to the cathode via an external power circuit. About the resulting stream stirring components of the Exoenzymfarm and / or the biogas reactor are operated, at least partially.

Ion permeable separators for separating the cathode from the anode are not particularly limited and are known in the art. Preference is given here to ion permeable, in particular H ⁺ permeable, membranes, such as, for example, proton exchange membranes (PEM), anion exchange membranes or electrolyte-filled filter paper. Such membranes are known in the art.

The following reactions preferably take place at the cathode and the anode of the device according to the invention. Anode: organ. fatty acids → n (acetate) + n (CO ₂ ) + n (e ^- ) organ. fatty acids → n (CO ₂ ) + n (e ^- ) H ₂ → 2 H ⁺ + 2e Cathode: O ₂ + 4 H ⁺ + 4 e ^- → 2H ₂ O

The said anodic reactions are carried out by the exoelektrogenen bacteria. In particular, either accumulating fatty acids are consumed and converted to substances that can be used as substrates by the methanogens, or hydrogen is directly converted. The resulting H ⁺ ions migrate through the ion-permeable separator to the cathode, where they are available for the cathode reaction. The resulting electrons (e ^- ) are electrically conducted to the cathode, where they are available for the cathode reaction. The oxygen required in the cathode reaction is preferably from the air. The cathodic reaction can be catalyzed by laccases formed in the exoenzyme farm during their transport through the cathode. In these processes, depending on the resistance of the consumer connected between anode and cathode, a certain anode and cathode potential is established.

The exoenzyme farm of the device according to the invention represents a device which can be charged with biomass, it being possible to cultivate aerobically living microorganisms on the biomass. These microorganisms are preferably fungi or bacteria that preferentially produce cellulases and laccases. These enzymes are preferably delivered to the surrounding medium. Such microorganisms are known in the art, and are for example members of the genera Trametes and Streptomyces. The biomass used in this context preferably consists predominantly of lignocellulosic biomass, for example wood chips or straw, in order to induce exoenzyme production. In a preferred embodiment, the exoenzyme farm contains a sprinkler system for irrigating the aerobically living microorganisms. Furthermore, the exoenzyme farm contains agents which direct the enzymes produced by the microorganisms out of the exoenzyme farm into the biogas fermenter. The enzymes are preferably passed through the cathode space, where they adsorb to the cathode and are there electrocatalytically active.

Further objects of the present invention relate to the use of the device according to the invention for the production of biogas and production of electrical energy, as well as methods for the production of biogas and production of electrical energy, comprising the provision and operation of a device according to the invention.

The innovations of a biogas plant according to the invention include the insertion of an anode into the fermenter and the stabilization of the processes taking place in the fermenter via the application of a specific potential. In process limitations, the potential of the anode is shifted to the positive to facilitate the delivery of electrons to the anode. Thus, the reduction of the concentration of organic acids and the hydrogen partial pressure is promoted. If the fermenter should run under standard conditions, the potential is not influenced from the outside and thus fall to values of about -200 mV against a normal hydrogen electrode. An exoenzyme farm also helps in the breakdown of complex biopolymers and makes them more accessible to the gezer. In addition, the formed laccases can catalyze the reactions at the cathode. By introducing an anode into the fermenter chamber, which is colonized with exoelektrogenen bacteria, the accumulation of organic acids can be counteracted, and thus the increase in hydrogen concentration and a consequent decrease in the pH can be prevented. By introducing exoenzymes from the Exoenzyme farm, polymers can be broken down more quickly and, in addition, the processes at the electrode can be catalyzed.

All this makes it possible to control the processes in the biogas fermenter, to stabilize the processes in the fermenter, and to generate additional electricity via a microbial fuel cell. In particular, exoelectrogenic organisms can breathe hydrogen and / or lower fatty acids in the fermenter space in the fermenter used in the fermenter. Thus, the hydrogen partial pressure can be lowered (electrosyntrophy) and lower fatty acids, which can contribute to a lowering of the pH, are removed (electrogenesis). A cathode on the outside of the fermenter forms the counter electrode for the anode and allows the production of electrical energy. Enzymes for the cathode and fermenter are produced in an exoenzyme farm. This allows a pre-treatment of the substrates for better digestion, a faster utilization of the substrates and higher biogas yields. Laccases act as a catalyst at the cathode and thus enable higher energy production.

• 1: Schematische Darstellung der Prozesse in einem Biogas-Fermenter, insbesondere der Hydrolyse, Acidogenese, Acetogenese und Methanogenese.
• 2: Schematischer Aufbau der erfindungsgemäßen Elektrobiogasanlage. Die Anode befindet sich im Inneren des Fermenters. An der Oberfläche der Anode befinden sich exoelektrogene Bakterien. Diese unterstützen die Acetogenese durch Elektrogenese und erniedrigen den Wasserstoffpartialdruck mittels Elektrosyntrophie. Die Kathode befindet sich außen am Fermenter und überträgt die Elektronen auf Sauerstoff.
• 3: Modell der aeroben Exoenzymfarm außerhalb des Biogas-Fermenters. Die Produktion von Polymer-abbauenden Enzymen, die durch die Kathode in den Fermenter geleitet werden, erleichtert den Substratzugang für die gärenden Bakterien. Die in der Exoenzymfarm entstehenden Laccasen erhöhen das Potential an der Kathode durch Katalyse der Sauerstoffreduktion.

The figures show:

• 1 : Schematic representation of the processes in a biogas fermenter, in particular the hydrolysis, acidogenesis, acetogenesis and methanogenesis.
• 2 : Schematic structure of the electrobiogas plant according to the invention. The anode is located inside the fermenter. On the surface of the anode are exoelektrogene bacteria. These support acetogenesis by electrogenesis and lower the partial pressure of hydrogen by means of electrosyntrophy. The cathode is located on the outside of the fermenter and transfers the electrons to oxygen.
• 3 : Model of the aerobic Exoenzyme farm outside the biogas digester. The production of polymer-degrading enzymes, which are passed through the cathode into the fermenter, facilitates the substrate access for the fermenting bacteria. The laccases produced in the exoenzyme farm increase the potential at the cathode by catalyzing the oxygen reduction.

The present invention will be further illustrated by the following non-limiting example.

Example 1:

In the context of the present invention, a microbial fuel cell is combined with a biogas fermenter ( 2 ). This will increase the efficiency of biogas production. For this purpose, anoelektrogene organisms are settled at an anode, which stabilize the biogas process. These organisms can metabolize products of acidogenesis such as formate, lactate or propionate and thus relieve the acetogenesis. In addition, they are able to use H ₂ as an electron donor and thus contribute to lower the hydrogen partial pressure. This process is adjustable by setting a certain anode potential. For these processes, the term electrogenesis or electrosyntrophy is proposed ( 2 ).

Further, according to the present invention, the degradation of the biomass is accelerated by an exoenzyme farm. For this purpose, aerobically living microorganisms are grown in an extra compartment outside the biogas fermenter ( 3 ). These microorganisms mainly produce cellulases and laccases, the former primarily helping to break down the biopolymers and the latter accelerating the reaction at the cathode. The produced enzymes are passed through the cathode into the fermenter and there accelerate the degradation of the substrate ( 3 ).

1. (i) Die polymere Biomasse wird schneller abgebaut.
2. (ii) Die Biomasse hat eine kürzere Verweilzeit im Fermenter.
3. (iii) Ein Teil der Biomasse wird direkt in elektrische Energie umgewandelt, ohne Konversion aus Methan.
4. (iv) Die Abläufe im Fermenter werden durch die Anode stabilisiert und möglichen Störungen dieser Abläufe entgegengewirkt.
5. (v) Die Reaktionen an der Kathode werden katalysiert.

The increase in efficiency of the device according to the invention for the production of biogas and production of electrical energy is thus achieved by the following factors:

1. (i) The polymeric biomass is degraded faster.
2. (ii) The biomass has a shorter residence time in the fermenter.
3. (iii) Part of the biomass is converted directly into electrical energy without conversion from methane.
4. (iv) The processes in the fermenter are stabilized by the anode and possible disturbances of these processes counteracted.
5. (v) The reactions at the cathode are catalyzed.

Claims (15)

Apparatus for producing biogas and for generating electrical energy, containing a biogas digester, an anode, the anode attached to the inside of the biogas digester, during operation of the biogas fermenter is at least partially in contact with the located in the biogas digester biomass, and is colonizable with exoelektrogenen bacteria, a cathode, wherein the cathode attached to the outside of the biogas digester, is electrically connected to the anode, and is separated from the anode by an ion permeable separator, and an exoenzyme farm, the exoenzyme farm is arranged outside the biogas digester, can be fed with biomass, and biomass in the exoenzyme farm is colonized with aerobically living microorganisms, and wherein in the Exoenzymfarm produced by the aerobically living microorganisms enzymes from the Exoenzymfarm via a line in the biogas fermenter can be introduced. Device after Claim 1 wherein the anode and / or the cathode consists of carbon materials, steel or titanium. Device after Claim 2 wherein the carbon materials are graphite, carbonized or carbon nanotubes. Device according to one of Claims 1 to 3 wherein the anode is populated by exoelectrogenic bacteria present in the biomass. Device according to one of Claims 1 to 3 in which the anode is colonized by preincubation with exoelectrogenic bacteria. Device according to one of Claims 1 to 5 wherein the exoelektrogenen microorganisms are members of the genus Geobacter or members of the genus Shewanella. Device according to one of Claims 1 to 6 wherein the cathode is an air breathing cathode. Device according to one of Claims 1 to 7 wherein the cathode is connected to the anode via an external circuit. Device according to one of Claims 1 to 8th wherein the ion permeable separator is an H ⁺ ion permeable membrane. Device according to one of Claims 1 to 9 wherein the aerobic microorganisms are cellulases and laccases producing bacteria or fungi. Device after Claim 10 , wherein the aerobic microorganisms are members of the genus Trametes or members of the genus Streptomyces. Device according to one of Claims 1 to 11 in which the enzymes produced in the exoenzyme farm by the aerobic microorganisms are cellulases and laccases. Device according to one of Claims 1 to 12 in which the enzymes produced by the aerobically living microorganisms can be introduced from the exoenzyme farm via a line through the cathode space into the biogas fermenter. Device according to one of Claims 1 to 13 wherein the exoenzyme farm further contains a sprinkler system for irrigating the aerobic microorganisms. Use of a device according to one of Claims 1 to 14 for the production of biogas and production of electrical energy.

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