EP1912900A1

EP1912900A1 - Method for producing biogas

Info

Publication number: EP1912900A1
Application number: EP06762885A
Authority: EP
Inventors: Gerhard RÖSING; Frank Keppler
Original assignee: Max Planck Gesellschaft zur Foerderung der Wissenschaften eV
Current assignee: Max Planck Gesellschaft zur Foerderung der Wissenschaften eV
Priority date: 2005-07-29
Filing date: 2006-07-28
Publication date: 2008-04-23
Also published as: DE102005058771A1; WO2007014717A1

Abstract

The invention relates to a method for producing biogas during which: (a) biomass is fermented under anaerobic conditions; with the exception that; (b) during the fermentation process, air and/or oxygen is/are dosed to the fermentation substrate containing the biomass. According to the invention, the method can be carried out in a single or multistage manner. In a preferred embodiment, a mechanical commutation of the substrate occurs before fermentation. The method is preferably used in the area of agricultural biogas production. In addition, an appropriate use in anaerobic refuse fermentation is possible, during which vegetable biomass can be used as a coenzyme on a case by case basis. The inventive method makes possible significantly higher yields of biogas than in prior art methods. In a particularly preferred embodiment, enzymes or algae preparations are added to the fermentation substrate.

Description

Process for the production of biogas

The invention relates to a process for the production of biogas, wherein (a) biomass is fermented under anaerobic conditions; with the exception that (b) during the fermentation process, the fermentation substrate comprising the biomass is metered in air and / or oxygen. According to the invention, the process can take place in one or more stages. In a preferred embodiment, the fermentation is preceded by a mechanical substrate comminution. The method is preferably used in the field of agricultural biogas production. In addition, an appropriate application in the anaerobic waste fermentation is possible, with plant biomass can be used as Koferment occasionally. The process according to the invention enables significantly higher biogas yields than processes known in the prior art. In a particularly preferred embodiment, enzymes or algae preparations are added to the fermentation substrate.

Various documents are cited in the text of this specification. The disclosure of the cited documents (including all manufacturer's descriptions, statements, etc.) is hereby incorporated by reference into this description.

Biogas is produced during the bacterial fermentation of organic matter under exclusion of air as a multi-stage process in the following series of steps.

1st hydrolysis

(Splitting of polymeric compounds by means of exoenzymes of fermentative bacteria into monomers).

2. Acidification phase

(Fermentation of fission products to organic acids, alcohol and hydrogen and carbon dioxide).

3. Acetic acid formation (reaction of the carboxylic acids and alcohols to acetic acid, hydrogen and carbon dioxide).

4. Methanogenesis

(Methane production, acetogenotrophic from acetic acid and hydrogenotrophic from hydrogen and carbon dioxide). In the one-step process of biogas production, the described degradation reactions take place simultaneously in a single reactor system. The reaction conditions can not be adapted to the individual biochemical environmental claims of the various microorganisms involved in substrate degradation. The single-stage is therefore a procedural compromise. In order not to have to take into account the entire process, the biochemical optimization is directed to the actual methane formation. In multi-stage processes, individual steps described in separate reaction vessels, which allows an optimization of the reactions of the individual steps, but results in a more complex plant construction.

In methanogenesis, the last step in biogas formation, the actual methane production takes place under anaerobic conditions. The methane bacteria involved are obligate anaerobes and utilize about 70% acetic acid and 30% hydrogen and carbon dioxide to form the methane. For an optimized methanogenesis process, a close spatial symbiosis between the H ₂ - producing, acetic acid - forming bacteria and the H ₂ - utilizing methanogenic bacteria is required.

The acetic acid-forming step is considered the limiting factor in this complicated process. Of importance is the hydrogen partial pressure, which can only be maintained in the presence of H ₂ - consuming methane bacteria, such that the acetic acid-forming bacteria mainly contain the desired acetic acid and not carboxylic acids (having a chain length of C ₃ -C ₆ ). , or even lactic acid, produce. These bacteria are metabolically active only at a low hydrogen partial pressure. The production of biogas is optimal only if the degradation rates in the listed sub-stages are comparable.

In addition, the gas production can be disturbed by certain inhibitors. Under certain circumstances, inhibitors have a toxic effect on the bacteria involved in biogas formation even at low concentrations and thus slow or stop the degradation of the fermentation substrate. Generally, a distinction is made between two groups of inhibitors. The first group includes substances that are entered in the biogas formation process together with the fermentation substrate. The second group contains substances which are formed during the whole process in one of the individual steps. Examples of inhibitors belonging to the first group include sodium (inhibiting from 6 up to 30 g / l; in adapted cultures from 60 g / l), potassium (inhibiting from 3 g / l), calcium (inhibiting from 2.8 g / l CaCl ₂ ), magnesium (inhibiting from 2.4 g / l MgCl ₂ ), some heavy metals or also branched fatty acids (eg iso-butyric acid, inhibiting already from 50 mg / 1). To the second group z. B hydrogen sulfide or ammonia counted. Hydrogen sulphide can significantly reduce biogas production even in concentrations of approx. 50 mg / 1 fermentation substrate. To remove the undesired hydrogen sulfide this is oxidized, for example by means of oxygen introduction into the gas space of the fermenter to elemental sulfur. The oxygen concentration in the biogas should remain below 5% in order to minimize the risk of explosion. Ammonia can mainly form when using protein-rich fermentation substrate. He stands in a pH-dependent equilibrium with the ammonium ions in solution. With a shift of the pH in the basic range, the equilibrium is on the side of the ammonia. If a concentration of dissolved ammonia of 0.15 g / l fermentation substrate is reached, inhibition of biogas formation may occur.

Another parameter named in the prior art which influences biogas formation is the pH of the fermentation substrate. The bacteria, which are necessary for the sequence of the individual steps of biogas formation, namely have different pH optima. Thus, the pH optimum of the bacteria of the hydrolysis and the acidification phase is 4.5 to 6.3. However, they can survive at slightly higher pH without being too limited in their activity. In contrast, it is stated in the prior art that the acetic and methanogenic bacteria preferably require a pH in the neutral range at 6.8 to 7.5. It follows that in a one-step process, ie when carrying out the entire process in a single reaction vessel, this pH range should be adhered to according to the prevailing theory. However, the advantage here is that the pH within the system usually sets itself, regardless of whether the process is one or more stages. This self-adjustment is carried out by the acidic and alkaline metabolic products of the bacteria involved in the individual steps (A. Schattauer and P. Weiland: Handbook Biogas production and use published by the Agency for Renewable Resources, Gülzow, 2005).

The individual stages of biogas formation depend on a balanced substrate supply. On the one hand, it is desirable that as much biogas as possible can be produced with the substrates used. On the other hand, however, it must also be ensured that Trace elements and nutrients for the bacteria themselves are present in sufficient quantity. With regard to the amount of biogas formed, it can be said that this is determined by the proportions of proteins, fats and carbohydrates in the fermentation substrate. Fat provides the highest biogas yield, followed by carbohydrates and protein. However, the methane content of the resulting biogas is highest for protein, followed by fat and carbohydrates (A. Schattauer and P. Weiland: Handbook Biogas Extraction and Utilization published by the Agency for Renewable Resources, Gülzow, 2005).

Furthermore, for the processes used in the prior art, the fermentation substrate used should have a balanced C / N ratio. If too much carbon and too little nitrogen is present, the existing carbon can not be fully implemented. Thus, not as much methane is produced as technically possible. Nitrogen surplus on the other hand may lead to the formation of the inhibitor ammonia (see above). For an undisturbed process flow, therefore, according to the prior art, the ratio of carbon to nitrogen should be in the range of 10-30. A sufficient nutrient supply of the bacteria is achieved with a C / N / P / S ratio of 600: 15: 5: 1 (A. Schattauer and P. Weiland: Handbook Biogas production and use published by the Agency for Renewable Resources, Gülzow, 2005).

Accordingly, a number of parameters are known in the prior art which interact with one another in the production of biogas and positively or negatively influence the expected yield of biogas. These parameters are easily manageable in the prior art by a person skilled in the art for an optimized biogas yield. Even with an optimized, based on previous findings adjustment of these parameters, the recoverable yield of biogas and thus also of methane, however, can be described as in need of improvement.

The object of the present invention was to provide a method with which significantly higher yields of biogas can be achieved. The solution to this problem is achieved by the embodiments provided in the claims.

Thus, the invention relates to a process for the production of biogas wherein (a) biomass is fermented under anaerobic conditions; with the exception that (b) during the Fermentation process the biomass comprehensive fermentation substrate metered air and / or oxygen is supplied.

The term "biogas" is defined as a product of anaerobic biodegradation of biomass, which typically contains about 45 to 70% methane, 30 to 55% carbon dioxide, small amounts of nitrogen, hydrogen sulphide and other trace gases actual energy sources.

"Biomass" is the organic substance of living or dead organisms or their excreta or degradation products called.

"Anaerobic conditions" are reaction conditions characterized by the absence of free or dissolved oxygen, Accordingly, the term "except" refers to the fact that the anaerobic fermentation process is externally supplied with air and / or oxygen.

"Fermentation" refers to energy-yielding, organic matter-decomposing metabolism processes that take place under anaerobic conditions.A fermentation is always due to the activity of anaerobic or facultative anaerobic micro-organisms (bacteria or fungi) different steps, for which different microorganisms are responsible.

"Fermentation substrate" means material intended for fermentation with the aim of obtaining biogas, which consists of or contains biomass as defined above In addition to biomass, the fermentation substrate may contain other substances, such as additionally added water or nutrient preparations, such as minerals for bacteria.

The term "air" is understood to mean the gas mixture of the earth's atmosphere, according to which air consists mainly of the two gases nitrogen (78%) and oxygen (21%) .At comparatively high concentrations, argon (0.9%) and carbon dioxide (0 Furthermore, the term "air" also includes so-called "technical air" of the same composition. "Technical air" is understood below to mean compressed air as used by various manufacturers (eg Linde AG, Pullach). in steel bottles is sold. Also included in the term air are gas mixtures containing at least 66% nitrogen and 20% oxygen, whereby the 100% missing parts may consist of noble gases or carbon dioxide.

"Oxygen (element symbol O) is a non-metallic element. As a diatomic odorless gas (O ₂ ), it occurs with a volume fraction of about 21% in the earth's atmosphere. Oxygen can be used in the process according to the invention as a commercially sold in steel cylinders gas mixture, wherein the gas mixture consists of at least 99.5% oxygen. Suitable admixtures are, for example, water, carbon dioxide, methane, ethane, ethene, ethyne, nitrous oxide or halogenated hydrocarbons.

The process of the invention breaks the taboo of the prior art that no oxygen may be introduced into the methane forming reactor. To date, no procedural solutions have been known or proposed in the state of the art which specifically introduce oxygen or atmospheric oxygen into the methane forming reactor in one- or two-stage or multi-stage process processes for biogas production. Rather, so far in the technological entry of z. B. vegetable biomass in the fermentation process strictly taken to prevent the risk of oxygen input by special technical devices.

It is known in the art that the supply of air is performed in the step of hydrolysis or acidification phase. In contrast, the method according to the invention also operates the introduction of oxygen directly into the methanogenesis. Preferably, the entry of atmospheric oxygen in the lower fermentation substrate filled reactor area. An effective homogenization technique, for example, leads to a good distribution of space in the thoroughly mixed reactor.

Significant advantages of the method according to the invention over the prior art are, on the one hand, a higher achievable biogas yield and, on the other hand, better pumping and flow properties due to the faster degradation of the biomass and, consequently, a lower tendency for floating and sinking layers. In particular, long-term experiments of the inventors with a high-performance reactor come to the surprising result that the oxygen is consumed immediately when air is introduced into the fermentation substrate in the reactor and the rate of gas formation increases, with simultaneous observation of further negative redox potentials. The optimum of methane production in the fermentation process is observed only at very negative redox voltages of, for example, about - 350 mV to below - 500 mV. Biogas plants with a high methane formation potential reach such values. It was possible to achieve yields which were up to 51% above the yield without supply of air or oxygen. Even after more than 40 hours of testing, the biogas development was still 23% higher than in non-air or oxygen treated material, the yield depends on the fermentation substrate used.

The superiority of the method according to the invention over the prior art methods is based on the fact that the rate of reaction of the fermentation process is increased by metered introduction of oxygen or air. This is possible for example by a faster degradation of plant biomass, in particular of cellulose and hemicellulose (see below).

As a result of laboratory and large-scale investigations, it was possible to prove that the introduction of air or oxygen leads in particular to the accelerated degradation of cellulose-containing substrates and to the formation of organic secondary products with intercalated terminal oxygen such as alcohols, aldehydes, esters and amides, which are now microbiologically are more easily degradable. This increases the nutrient availability for the methanogenic microorganisms. The higher degradation rates due to the influence of oxygen consequently lead to higher throughput rates, gas productivities and gas yields in the reactor. The process can be run as a high-performance process. The degradability of the high polymer compounds is ensured, for example, by a microbial diversity of aerobic, anaerobic and facultatively anaerobic microorganisms or by the presence of enzymes or algae preparations.

It should also be emphasized that the parameters mentioned in the introduction and known in the prior art for optimizing the biogas yield do not cause any complications in the implementation of the process according to the invention and are therefore readily manageable by a person skilled in the art even in the process according to the invention. In terms of process technology, it is therefore possible (with the exception of the modification according to the invention) to be retained on established processes and at the same time a significantly improved yield of biogas can be achieved. In a preferred embodiment, the invention relates to a process which can proceed in one stage.

A "one-step process" is used when the four steps of biogas formation (hydrolysis, acidification phase, acetic acid formation, methanogenesis) take place in a reaction vessel (fermenter).

Single-stage processes have the advantage that costs can be saved by the reduced structural complexity required for the construction of the plant used. On the other hand, it is disadvantageous that the sensitivity of the methanogenic microorganisms to changed environmental conditions has the consequence that the reaction conditions have to be adapted to them. Thus, the microorganisms responsible for the other steps no longer work under optimal conditions and therefore have lower degradation rates. With the method according to the invention it is now possible, for example in single-stage plants, to increase the biogas yield and nevertheless to work in a medium which is oriented to the requirements of the methane-forming microorganisms.

In a further preferred embodiment, the invention relates to a method that runs in multiple stages.

If the hydrolysis and acidification phases are carried out spatially separated from the steps of acetic acid formation and methanogenesis, this is called a "multi-stage process." The multi-stage processes include, for example, two-stage processes.

The multistep offers the advantage that the reaction conditions can be adapted to the individual requirements of the microorganisms involved in the respective step, in order thereby to achieve higher degradation efficiencies. On the other hand, the disadvantageous aspect is the more complex design of the systems, which leads to higher investment costs.

In another embodiment, the invention relates to a one-step wet fermentation process for the anaerobic fermentation of liquid and / or solid manure and plant biomass for the purpose of generating biogas, characterized in that to achieve greater Reaction rates of the fermentation substrate periodically and metered air or oxygen is supplied. The feeding takes place in such a way that there is no damaging effect on the obligate anaerobic methane-forming microorganisms and a higher gas formation rate or yield from the biomass to be fermented is achieved by the aerobic treatment step. Due to the higher nutrient availability, process development represents a high-performance process in biogas production.

In a particularly preferred embodiment, the supply of air and / or oxygen in the multi-stage process in the methane forming reactor.

By "methane forming reactor" is meant in the following the reaction vessel in which the methanogenesis takes place.This is by definition the reactor in which all four steps of the biogas formation take place in the one-step process.In the multistage process it is the reactor in which the last two steps The other reactors are usually named after the respective step which takes place in them. As already mentioned above, the air and / or oxygen is supplied to the fermentation substrate.

In a further preferred embodiment, the supply of air or oxygen takes place at time intervals.

In the following, "time intervals" is understood to mean the periodic supply of air or oxygen, air or oxygen being supplied for a specific duration (time t ₁ ) and subsequently no air or oxygen being supplied for a specific duration (time t ₂ ). It is preferable that t, in the range of 5 to 30 minutes, more preferably about 20 minutes.

The periodic supply of air or oxygen, for example, offers the advantage that by permanently controlling the oxygen consumption, the metering of the air or oxygen input can be adjusted so that damage to the methane-forming microorganisms can be prevented. In addition, the amount and duration of the entry are, for example, dependent on the microbiological status of the fermentation substrate and especially useful if there are O ₂ - utilizing microorganisms (see below). In a further particularly preferred embodiment, the time intervals are selected so that the ratio of the duration of the air or oxygen supply (t,) to the duration of the time during which no supply takes place (t ₂ ) is below 0.2.

In another preferred embodiment, the dosage of the air or oxygen entry is selected so that the oxygen concentration is less than 0.1 mg / 1 O ₂ in fully mixed fermentation substrate.

The "fully mixed fermentation substrate" is understood as meaning the substrate which has been brought into complete contact with the introduced air or the introduced oxygen by stirring, for example stirring slowly and intermittently, rapidly with interruptions or continuously For example, it is designed so that a full mixing of the reactor, depending on the oTS content is achieved.

The measurement of the oxygen concentration takes place in the fermentation substrate, preferably at different measuring points. Commercially available measuring instruments, such as, for example, oxygen electrodes (for example from Nanodox, Lichtenstein) are used to measure the oxygen concentration. The oxygen concentration can be determined, for example, as an average value by a respective measurement at different positions in the reactor.

Furthermore, a careful metrological monitoring of the fermentation process is preferred, including the measurement and analysis of the following parameters:

• Temperature behavior »pH value

• Equivalents of the volatile fatty acids

• Determination of dry matter contents

• Recording the substance potentials and the C / N ratio

• Composition and amount of biogas • Continuous measurement of the O ₂ content in the fermentation substrate, preferably 2

measuring points

• Monitoring of the redox voltage

The parameters mentioned can be determined by a person skilled in the art by means of customary measuring and determination methods. In summary, and in accordance with the preferred embodiments of the invention discussed above, the oxygen input, in addition to the microbiological findings, is made dependent on the following criteria:

• O ₂ content <0.1 mg / 1 (see above) • pH preferably 6.5 to 8.5 (see above)

• ORP voltage: <-100 mV to - 600 mV

• Volatile organic acids or fatty acids preferably <2000 mg / ml

• t, approx. 20 min (see above)

• t, / t ₂ <0.1 (see above)

In a further preferred embodiment, the fermentation is preceded by a mechanical substrate comminution.

The term "mechanical substrate comminution" refers to the reduction of the average size of the individual constituents of the fermentation substrate by the action of physical forces The advantage of the mechanical substrate comminution lies in the enlargement of the surface of the substrate, making it more accessible to microorganisms.

In a further particularly preferred embodiment, the mechanical substrate comminution is achieved by extrusion, chopping or grinding.

By "extrusion" is meant a process in which materials are continuously pressed by means of a screw press via a working channel through a matrix and thus homogenized.

By "shredding" is meant the shredding of materials, in particular by means of moving knives.

"Grinding" refers to the comminution of materials using mills, for example rollers, balls or crushers.

In a further preferred embodiment, the fermentation takes place at temperatures of 38 to 55 ° C. Particularly preferred is a mesophilic temperature range of 40 to 42 ° C. Under ,. Temperature "is understood to mean the temperature prevailing in the methane forming reactor, whereby the temperature can be determined, for example, from continuous measurements at spatially different positions in the reactor.

Higher temperatures during fermentation according to the prior art result in a higher gas yield. The disadvantage here, however, the necessity of heating the fermentation substrate, since the heat of the microorganisms is not sufficient to maintain the required temperatures. It can be achieved with the inventive method a significant increase in efficiency, since at temperatures of 40 to 42 ° C higher yields than previously known in the art for this temperature range, can be achieved.

In a further preferred embodiment, the Faulraumbelastung is more than 3 kg oTS / m ³ x d. In a further particularly preferred embodiment, the Faulraumbelastung is more than 7 kg oTS / m ^ x d.

"Faulraumbelastung" is the amount of organic dry matter (oTS) in kilograms, which is the methane forming reactor per m ¹ volume and time unit is supplied.

In the prior art, a preferred Faulraumbelastung of 3 kg oTS / Wx d is assumed, in which a trouble-free, yield-optimized operation of the system is possible. With the method according to the invention it is now possible, for example, to control digester loads of more than 3 kg oTS / m.sup.dd and even more than 7 kg o.sup.T / m.sup.-d. This can be z. B. achieve a much higher energy density than previously known in the art, which also leads to higher yields of biogas.

In another preferred embodiment, optionally anaerobic microorganisms are present in the fermentation substrate.

By "facultative anaerobic microorganisms" is meant microorganisms which can both breathe oxygen under ATP formation and produce ATP in its presence by fermentation, whereas aerobic microorganisms generate ATP only in the presence of free or dissolved oxygen, while anaerobic microorganisms rely on the absence of oxygen. Aerobic microorganisms are z. B. actinobacteria or certain fungi. Anaerobic microorganisms are the methane-forming microorganisms or clostridia and optionally anaerobic z. B. Enterobacteriaceae such as E. coli. If algae preparations or enzymes are used (see below), the technologically registered oxygen may also be consumed by them. If these are not used, the presence of the facultatively anaerobic microorganisms is absolutely necessary in order to consume the oxygen.

The continuous methane formation is made possible, for example, by the presence of facultative anaerobes, which can exist under short-term oxygen influences, consume the oxygen in a timely manner and thus take over a protective function for the obligate anaerobic methane bacteria. Furthermore, the consumption of oxygen, for example, by enzymes or algae preparations done (see below).

In a further preferred embodiment, the facultatively anaerobic microorganisms are fungi. In a particularly preferred embodiment, the fungi are unicellular. In a further particularly preferred embodiment, the unicellular fungi belong to the yeasts.

In a further preferred embodiment, the facultative anaerobic microorganisms are bacteria. Particularly preferably, the bacteria belong to the families of Enterobacteriaceae or Vibrionaceae. In a further particularly preferred embodiment, the Enterobacteriaceae are selected from the genus Alterococcus, Aranicola, Arsenophonus, Averyella, Brenneria, Buchnera, Budvicia, Buttiauxella, Candidatus, Phlomobacter, Cedecea, Citrobacter, Dickeya, Edwardsieila, Enterobacter, Erwinia, Escherichia, Ewingella, Grimontella , Hafnia, Klebsiella, Kluyvera, Leclercia, Leminorella, Moellerella, Morganella, Obesumbacterium, Pantoea, Pectobacterium, Photorhabdus, Plesiomonas, Pragia, Proteus, Providencia, Rahnella, Raoultella, Salmonella, Samsonia, Serratia, Shigella, Tatumella, Thorsellia, Tiedjeia, Trabulsiella , Wigglesworthia, Xenorhabdus, Yersinia or Yokenella. More preferably, the bacteria of the family Vibrinaceae selected from the genus Allomonas, Catenococcus, Enterovibrio, Ferrania, Grimontia, Listonella, Photobacterium, Photococcus, Salinivibrio or Vibrio. Often, microorganisms are already present in the fermentation substrate or in the biomass. According to the invention, however, the addition of microorganisms is envisaged in order to further increase the yields. For this purpose, individual members of the aforementioned genera, as well as suitable mixtures of these can be added. Suitable mixtures include mixtures of members of the genera Escherichia or Kluyvera.

In the presence of the facultative anaerobic microorganisms, the oxygen introduced according to the invention can be breathed by them. Thus, on the one hand, a death of the methane-forming microorganisms is prevented and, on the other hand, a higher reaction kinetics is achieved by the significantly shorter generation doubling time of the facultatively anaerobic microorganisms since these split the cellulose and / or hemicellulose into readily biodegradable intermediates.

The process according to the invention can be carried out using various microorganisms which can ferment the said substrates. Examples of such microorganisms are psychrophilic microorganisms. In a further preferred embodiment, however, the fermentation is carried out by mesophilic or thermophilic microorganisms.

"Mesophilic microorganisms" are understood to mean microorganisms which have their growth optimum in a temperature range of, for example, 32 to 42 ° C.

Examples of mesophilic microorganisms are most eubacteria. "Thermophiles

Microorganisms ", however, have their optimum temperature preferably at temperatures of 50 to 57 ⁰ C. Examples of thermophilic microorganisms can be found especially among the

Archaea. However, there are also thermophilic representatives among the Gram-positive bacteria, such as. B among the classes of Clostridia and Bacilli. Examples include Clostridiales, Halanaerobiales or Thermoanaerobacteriales for the class of

Clostridia and Lactobacillales or Bacillales for the class Bacilli.

In a further preferred embodiment, the thermophilic or mesophilic microorganisms are selected from the classes of Methanomicrobia or Methanobacteria. Examples of members of these classes can be found among the families of Methanoplanaceae, Methanosarcinaceae or Methanobacteriaceae. These families include, but are not limited to, the genera Methanogenium, Methanospirillum, Methanoplanus, Methanosarcina, Methanococcoides, Methanotrix, Methanolobus or Methanothermobacter. Examples of the Genus Methanogenium are the species M. cariaci, M. marisnigri, M. olentangyi, M. thermophilicum. M. aggregands. M. bourgense or M. tationis. An example of the genus Methanospirillum is the species M. lungatei. Examples of the genus Methanosarcina are M. limicola, M. barkeri, M. mazei. M. thermophila, M. acetivorans or M. vacuolate. An example of the genus Methanococcoides is M. methylutents. Examples of the genus Mathanotrix are M. soehngenii or M. concilli. An example of the genus Methanolobus is M. tindarius. An example of the genus Methanothermobacter is M. thermoautotrophicus. These microorganisms are often already present in the fermentation substrate or in the biomass. According to the invention, however, the addition of microorganisms is envisaged here in order to further increase the yields. For this purpose, individual members of the aforementioned genera, as well as suitable mixtures of these can be added. Suitable mixtures include M. soehngenii with M. thermoautotrophicus (formerly Methanobacterium thermoautrophicum), e.g. B. are known as CO ₂ - reducer.

In another preferred embodiment, the fermentation substrate consists of or contains plant biomass, zoomasse, biowaste or animal excreta.

By "vegetable biomass" is meant biomass consisting of plants or parts of plants, such as dried plants or parts of plants, or fresh plants or parts of plants, such as sudangras, banana leaves or hay.

In a particularly preferred embodiment, the vegetable biomass contains cellulose, hemicellulose or lignocellulose.

"Cellulose" is an unbranched polysaccharide consisting of several hundred to ten thousand ß-glucose molecules linked by a (1-4) ß-glycosidic linkage.Cellulose is the main constituent of plant cell walls and thus in almost all plants Only a few species of algae, such as the Bangiophycidae, do not contain any cellulose at certain stages of development.

"Hemicellulose" is a collective name for polysaccharides derived from various hexoses (eg glucose, mannose, galactose) and / or pentoses (eg arabinose, xylose) are constructed. If it is made up only of hexoses it is called hexosans, it is pentoses of pentoses. Hemicellulose comes z. B. reinforced in grain.

'Lignocellulose' 'is a combination of cellulose and lignin, which serves as a supporting substance in wood cells. Lignocellulose is found mainly in wood.

In a further preferred embodiment, the invention relates to a method in which fermentation substrates having an above-average proportion of plant biomass to be fermented are used. The proportion of vegetable biomass is so high that an OTS content of more than 12%, preferably more than 15%, such as more than 20% is achieved in the reactor.

In a further particularly preferred embodiment, the vegetable biomass is straw, which according to the invention is preferably used in admixture with other biomass.

With the method according to the invention it is also possible to use straw as a fermentation substrate. This proves, for example, to be particularly advantageous, since straw is obtained in particular in this country by its use as a stable infestation in animal husbandry and as a by-product of grain production in large quantities.

For example, "zoomasse" refers to dead animals or parts of dead animals, some of which are also processed, but which are not decomposed or digested by other living things, such as butchers' products such as meat, sausages , Fish products or residues which are produced in the production of these, preference is given to those materials which have a high fat content.

"Bio-waste" is material of animal or plant origin that can be degraded by microorganisms, soil organisms or enzymes secreted by it, or it may already be in decomposition Examples of biowaste include superimposed and thus non-edible food, kitchen waste and canteen waste, fat waste or waste from the food and feed industries. "Animal waste" is the excrements of animals of all kinds, examples being manure, manure or guano, but also manure that is mixed with straw or other bedding materials, but according to the invention despite admixture of vegetable products under the term "animal excretions""' to be led.

In a particularly preferred embodiment, the animal excretions are or contain manure or solid manure.

"Manure" is a mixture of animal excrement (excrement and urine) as well as water and sometimes also bedding like straw.

"Solid manure" is a stackable mixture of animal excrement and bedding, which may contain, for example, leftover food as well as drinking and cleaning water.

In another preferred embodiment, enzymes or algae preparations are added to the fermentation substrate.

As is known, "enzymes" are proteins which catalyze chemical reactions, for example they can occur within the cell membrane of a cell as so-called endoenzymes or are located on the outside of the cell membrane as exoenzymes or are excreted by cells in the groups of oxidoreductases, hydrolases or lyases, and they can be used in various dosage forms, for example in the form of pellets, liquid or in powder form.

The term "algae" refers in a broader sense to water-borne, plant-like creatures that carry out photosynthesis. "Algae preparations" are understood to mean fresh algae as well as dosage forms of algae of any kind. These dosage forms can, for. B. dried and in powder form, as an extract or in a suspension. Preferably, the enzymes present in the algae preparations are still functional.

With the method according to the invention, a significant increase in the biogas yield could be achieved by the addition of algae preparations. Algae preparations are particularly preferred because of their lower cost compared to enzymes. Without the applicant If it is bound to be bound by a particular theory, it is assumed that the addition of algae preparations or enzymes can at least partially convert the supplied (air) oxygen.

In a particularly preferred embodiment, the addition of the enzymes or algae preparations takes place before, during or after the mechanical substrate comminution.

The addition of the algae preparations or the enzymes before or during the mechanical comminution, for example, facilitate the comminution of the fermentation substrate by the biological macromolecules such. As cellulose, be partially digested even before the actual crushing. Furthermore, the enzymes or algae preparations can already be mixed with the fermentation substrate by the comminution step. An addition after the mechanical substrate comminution offers, for example, the advantage that the already comminuted fermentation substrate comes into closer contact with the enzymes or algae preparations due to its enlarged surface area.

In a further particularly preferred embodiment, the enzymes used are cellulases, hemicellulases, xylanases or pectinases. Other enzymes that can be used, for example, are lipases or proteases.

In a further particularly preferred embodiment, the algae preparations are obtained from marine macroalgae.

The term "macroalgae" refers to the species of algae whose habit is not microscopic algae or single cells, but which are visible to the naked eye, and species that meet these requirements occur, for example, within the brown, red and green algae ,

In a further particularly preferred embodiment, the marine macroalgae are brown or red algae.

"Brown algae" (or Phaeophyta) are marine, brown algae with generational changes A characteristic of these filamentous or leafy, in any case, mostly multicellular protists are brown dyes that mask the green chlorophyll.The brown algae include the orders Ascoseirales, Cutleriales, Desmarestiales, Dictyotales, Ectocarpales, Fucales, Heterochordariaceae, Laminariales, Ralfsiaceae, Scytothamnales, Sphacelariales, Sporochnales, Syringodermatales or Tilopteridales. The order of the fucales includes the families of Durvillaeaceae, Fucaceae, Himanthaliaceae, Hormosiraceae, Notheiaceae, Sargassaceae or Seirococcaceae. The Fucaceae family includes the genera Ascophyllum, Fucus, Hesperophycus, Pelvetia, Pelvetiopsis, Silvetia or Xiphophora. The genus Ascophyllum includes the species Ascophyllum nodosum.

"Red algae" (Rhodophyta) are mostly marine algae, which have in common that the antennae for photosynthesis contain a red dye, for example, the red algae include the Bangiophyceae, Florideophyceae or Goniotrichales.

In a further particularly preferred embodiment, the brown algae Ascophyllum nodosum is used.

With the method according to the invention, a significant increase in the biogas yield could be recorded, in particular with the use of the brown algae Ascophyllum nodosum.

In a further particularly preferred embodiment, the enzymes or algae preparations are used in a concentration of 1 g / kg oTS.

With the method according to the invention could be achieved using this concentration of enzymes or algae preparations, a particularly advantageous increase in biogas yield, in particular with algae preparations a better price / performance ratio than in enzymes was found.

The figures show:

Figure 1: Schematic representation of the time course of the periodic air entry

Shown is the time course of the air intake, including the measured O ₂ - contents in a fermentation substrate. The dosage with atmospheric oxygen was so dimensioned that the inhibitory effect of oxygen with limit values of 0.1 mg / l was clearly undercut.

The strong decrease of the O ₂ - content after completion of the air supply speaks for the high degree of oxygen depletion. The faster this waste occurs, the better the rate of degradation and methane formation. FIG. 2: Time dependence of the biogas rate from the air intake

Shown is the temporal dependence of the biogas rate from the air intake into the fermentation system. Even the untreated starting substrate shows a high gas formation rate. With the periodic air supply, the evolution of gas increases explosively, drops relatively evenly in the subsequent rest phase to continue the process at a slightly lower level in the subsequent entry. In the continuous flow fermentation process can be held relatively constant by substrate feed the set high level of gas production.

Ii:

O ₂ Oxygen content t Time ti Time span of air intake t ₂ Time interval between the periodic air inputs mg milligrams mV millivolts

1 liter

BG Biogas m ³ Biogas volume (measured) m ³ _F Reactor volume d day h hour min minute kg oTS kg organic dry matter

The examples illustrate the invention.

Example ϊ: Implementation of the process according to the invention in a pilot plant

In May 2003, the pilot plant with a capacity of 800m ³ was put into operation. Yields have since been continuously increased. In terms of comparability, the fermentation substrate consists of 23.1 t of cattle slurry, 3.8 t of solid manure, 6.9 t of grass silage and 0.9 t of grain. The supply of oTS was with this fermentation substrate 4805 kg / d. This resulted in a digested load of 6.01 kg oTS / W _F x d. The gas productivity before the beginning of the cyclic air intake was 2.42 m ¹ x d. In October 2005, the cyclical air intake and the addition of 4.8 kg algae preparations per day (Ascophyllum nodosum from Biofermat) were started. In this case, per day for 160 min in 8 intervals of 20 min (t,) air was entered into the methane forming reactor. The total amount of registered air was 90 mVd. Due to the cyclic air entry, the gas productivity was 3.18 m ³ xd be increased. This corresponds to an increase of 31%. The oxygen content in the fermentation substrate remained continuously below 0.02 mg / l at a pH of 7.8 and an ORP of -380 mV to -560 mV. The concentration of free fatty acids was below 500 mg / l. The plant was operated at a temperature of 40 to 42 ° C.

Example 2: Laboratory Investigations for the Influence of Oxygen

In a laboratory experiment, the same fermentation substrate as in Example 1 was used in a reaction vessel with a volume of 1 liter. With addition of the same

Algae preparations in the same concentration under otherwise comparable conditions was then blown into the reactor for a period of 40 hours every 14 hours for 15 minutes. The entry dose in air was higher by a factor of 5 than in the pilot plant

(Example 1). The biogas yield could be increased by more than 200% due to the cyclical introduction of air (see FIG. 2).

Claims

claims

1. Process for the production of biogas, wherein

(a) biomass is fermented under anaerobic conditions; with the exception that

(b) during the fermentation process the fermentation substrate comprising the biomass is dosed with air and / or oxygen.

2. The method of claim 1, wherein the method is single-step.

3. The method of claim 1, wherein the method is multi-stage.

4. The method of claim 3, wherein in the multi-stage process, the supply of air and / or oxygen takes place in the methane forming reactor.

5. The method according to any one of claims 1 to 4, wherein the supply of air and / or oxygen takes place in time intervals.

6. The method of claim 5, wherein the time intervals of air supply and interruption of the air supply are selected so that their ratio is less than 0.2.

7. The method according to any one of claims 1 to 6, wherein the metering of the air or oxygen input takes place so that the oxygen content in the fully mixed fermentation substrate is less than 0.1 mg / 1 O ₂ .

8. The method according to any one of claims 1 to 7, wherein the fermentation is preceded by a mechanical substrate comminution.

9. The method of claim 8, wherein the mechanical substrate comminution by Hxtrusion, chaffing or grinding takes place.

10. The method according to any one of claims 1 to 9, wherein the fermentation takes place at a temperature of 38 to 55 ⁰ C.

1 1. A method according to any one of claims 1 to 10, wherein the Faulraumbelastung is more than 3 kg oTS / m ³ xd.

12. The method according to any one of claims 1 to 1 1, wherein optionally anaerobic microorganisms in the fermentation substrate are present.

13. The method according to any one of claims 1 to 12, wherein the biogas production is carried out by mesophilic or thermophilic methane-forming microorganisms.

14. The method according to any one of claims 1 to 13, wherein the fermentation substrate of vegetable

Biomass, zoomasse, biowaste or animal excreta contains or contains.

15. The method of claim 14, wherein the vegetable biomass comprises cellulose, hemicellulose or lignocellulose.

16. The method of claim 15, wherein the vegetable biomass is straw.

17. The method of claim 14, wherein the animal excretions consist of or contain manure or manure.

18. The method according to any one of claims 1 to 17, wherein enzymes or algae preparations are added to the fermentation substrate.

19. The method of claim 18, wherein the addition of the enzymes or algae preparations before, during or after the mechanical substrate comminution takes place.

20. The method according to claim 18 or 19, wherein the enzymes are cellulases, hemicellulases, xylanases or pectinases.

21. The method according to claim 18 or 19, wherein the algae preparations are obtained from marine macroalgae.

22. The method of claim 21, wherein the marine macroalgae are brown or red algae.

The method of claim 22, wherein the brown alga is Ascophyllum nodosum. 5

24. The method according to any one of claims 18 to 23, wherein the concentration of the enzymes or the algae preparations is 1 g / kg oTS.

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