DE102005058771A1 - Modified one-step wet fermentation process for biogas production - Google Patents

Abstract

The invention relates to a process for the production of biogas, in which an anaerobic digestion of liquid and / or solid manure and vegetable substrates takes place in a single-stage wet fermentation process.
The invention has for its object to provide a method by which a significant increase in the reaction rate and the associated higher performance indices of the fermentation process is achieved.
The object is achieved by a method in which the fermentation substrate periodically and metered oxygen is supplied to achieve greater reaction rates.

Description

The The invention relates to a process for the production of biogas, in which in a one-step wet fermentation process an anaerobic digestion of liquid and / or solid manure and vegetable substrates.

The Process is preferably in the field of agricultural Biogas production applied. About that In addition, a suitable application in anaerobic waste fermentation is possible, and also Vegetable biomass can be used as a coferment on a case by case basis.

• 1. Durch Hydrolyse erfolgt eine Aufspaltung polymerer Verbindungen mit Hilfe von Exoenzymen fermentativer Bakterien in Monomere.
• 2. In einer Versäuerungsphase erfolgt die Vergärung der Spaltprodukte zu organischen Säuren, Alkohol sowie Wasserstoff und Kohlendioxid.
• 3. Durch Umsetzung der Carbonsäuren und Alkohole zu Essigsäure, Wasserstoff und Kohlendioxid wird der reaktionskinetisch bedeutsame dritte Verfahrenschritt gekennzeichnet.
• 4. Darauf aufbauend erfolgt die Methanerzeugung, acetogenotroph aus Essigsäure sowie hydrogenotroph aus Wasserstoff und Kohlendioxid.

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

• 1. By hydrolysis, a breakdown of polymeric compounds by means of exoenzymes of fermentative bacteria into monomers takes place.
• 2. In an acidification phase, the digestion of the fission products to organic acids, alcohol and hydrogen and carbon dioxide takes place.
• 3. Reaction of the carboxylic acids and alcohols to acetic acid, hydrogen and carbon dioxide characterizes the reaction kinetically significant third process step.
• 4. Based on this, methane production takes place, acetogenotrophically from acetic acid and hydrogenotrophic from hydrogen and carbon dioxide.

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 methane bacteria is required.

The acetate-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 acetogenic bacteria mainly contain the desired acetic acid and not carboxylic acids (C ₃ -C ₆ ) or even lactic acid , to 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.

at Presence of so-called facultative anaerobic microorganisms in the Reactor can breathe technologically registered atmospheric oxygen become. These bacterial groups can both under the influence of oxygen and completely without oxygen Metabolic processes practice and thus prevent the death of methane-forming Microorganisms. Unlike the methanogenic bacteria, these require a significantly shorter generation time for cell duplication, which a significant increase the reaction kinetics may result.

It It is known that, for example, the propionibacteria in the digestive organs of ruminants over catalases feature, which enable them to be both anaerobic and aerobic to grow. Controlled air supply (ruminating) is the cell yield several times higher as under strictly anaerobic conditions. The Propionibakterien ferment successfully Glucose, lactose, mannose and glycerol to propionate. However, measurable oxygen partial pressures can toxic.

in the State of the art, no procedural solutions are known in one-step process processes for biogas production oxygen or enter atmospheric oxygen in the reactor to specifically a faster Removal of cellulose-containing biomass to achieve. Rather, when technological entry of plant substrates in the fermentation room Attention, the danger of the oxygen entry by special to prevent technical devices.

Of the Invention is based on the object, a method of the initially specify the type mentioned, with a significant increase in the Reaction speed and the associated higher performance ratios the fermentation process is achieved.

According to the invention Task with a method which the features specified in claim 1 has dissolved.

advantageous Embodiments are specified in the subclaims.

at the method according to the invention it is a modified one-step wet fermentation process for biogas production with an above-average high proportion to be fermented vegetable biomass. This is usually a short-term, time-controlled Metered entry of atmospheric oxygen in a reactor.

With The method is used to achieve higher reaction rates the fermentation process Oxygen is supplied in a metered dose for a short time so that it does not reach any one damaging Effect on obligate anaerobic methanogenic microorganisms comes and through the aerobic treatment step, a higher gas formation rate or yield from the to be fermented Biomass is achieved. The process development is due the higher one nutrient availability a high-performance process in biogas production.

The Presence of so-called facultative anaerobes leads to immediate consumption of the registered oxygen with the consequential effect a splitting of the high polymer compounds (e.g., cellulose and hemicellulose) in easily degradable intermediates with embedded terminal Oxygen such as alcohols, aldehydes, esters, amides and carboxylic acids.

It is advantageous to perform a metrological monitoring of the fermentation process, with particular consideration of O ₂ - levels and their degradation, the redox voltages and the levels of volatile organic fatty acids in the fermentation substrate.

The demonstrably higher Rate of degradation of plant biomass leads to a more favorable pumping and fluidity of the fermentation substrate and a lower tendency to swim and Sinkschichtenbildung and lets Therefore, extremely high energy densities (digester loads), without that this is to the detriment of the biogas yield.

Further Is it possible, that a technological combination with other digestion methods Mechanical Substrate Preparation (e.g., Extrusion, Intensive Reduction) or the enzymatic treatment of the fermentation substrate can be used.

• 1. Mit dem erfindungsgemäßen Verfahren gelingt es, durch dosierten Eintrag von Sauerstoff die Reaktionsgeschwindigkeit des Vergärungsvorganges zu erhöhen. Dabei erfolgt ein schneller Abbau pflanzlicher Biomasse, insbesondere von Cellulose und Hemicellulose. Die Abbaubarkeit der hochpolymeren Verbindungen kann beispielsweise durch eine mikrobielle Vielfalt von Pilzen und aerob arbeitenden Actinobakterien sowie anaeroben Clostridien und fakultativ anaeroben Mikroorganismen gewährleistet werden.
• 2. Im Ergebnis labor- und großtechnischer Untersuchungen konnte der Nachweis erbracht werden, dass der Eintrag von Luftsauerstoff zum beschleunigten Abbau cellulosehaltiger Substrate und zu organischen Folgeprodukten mit eingelagertem endständigen Sauerstoff wie beispielsweise Alkohole, Aldehyde, Ester und Amide führt, die nun mikrobiologisch leichter abbaubar sind. Damit wird die Nährstoffverfügbarkeit für die methanbildenden Mikroorganismen erhöht; der Prozess trägt Turbocharakter.
• 3. Im einstufigen Prozess der Methanvergärung laufen die beschriebenen Abbaureaktionen in einem einzigen Reaktorsystem simultan ab. Dabei können die Reaktionsbedingungen nicht an die individuellen biochemischen Milieuansprüche der verschiedenen am Substratabbau beteiligten Mikroorganismen angepasst werden. Die Einstufigkeit ist deshalb ein verfahrenstechnischer Kompromiss. Um nicht auf den Gesamtprozess Rücksicht nehmen zu müssen, ist die biochemische Optimierung auf die eigentliche Methanbildung gerichtet.
• 4. Obwohl von der Fachwissenschaft einheitlich die Auffassung vertreten wird, Sauerstoff vom eigentlichen Methanbildungsprozess fernzuhalten, kommen Langzeitversuche der Erfinder mit einem Hochleistungsreaktor zu dem überraschenden Ergebnis, dass beim Einleiten von Luftsauerstoff in den Reaktor dieser sofort verbraucht wird und die Gasbildungsrate ansteigt, unter gleichzeitiger Beobachtung sich weiter negativ entwickelnder Redoxspannungen.
• 5. Die höheren Abbaugeschwindigkeiten infolge Sauerstoffeinfluss führen folgerichtig zu größeren Durchsatzleistungen, Gasproduktivitäten und Gasausbeuten im Reaktor. Der Prozess kann als Hochleistungsprozess gefahren werden.
• 6. Menge und Dauer des Eintrags sind in hohem Maße vom mikrobiologischen Status des Gärsubstrats abhängig. Der Eintrag ist nur dann sinnvoll, wenn O₂ – verwertende Mikroorganismen dort in ausreichender Anzahl vorhanden sind. Die Begleitflora aus kulturell aeroben Keimen sind Pilze sowie O₂ – zehrende gramnegative Bakterien; sie dienen in entscheidendem Maße einer optimalen Biozönose als Precursor für die Methanogenese. Die kontinuierliche Methanbildung wird ermöglicht durch die Anwesenheit so genannter fakultativer Anaerobier, die unter kurzzeitigen Sauerstoffeinflüssen existieren können, diesen zeitnah verzehren und somit eine Schutzfunktion für die obligat anaeroben Methanbakterien übernehmen.
• 7. Bei periodischer Belüftung von Gärsubstrat konnte die ursprüngliche Biogasrate bis zu maximal 51 % gesteigert werden. Selbst nach wiederholtem Eintrag von Luftsauerstoff lag die Biogasentwicklung nach über 40 Stunden Versuchsdauer noch um 23 % höher als bei unbehandeltem Material.
• 8. Nachgewiesenermaßen wird mit der Sauerstoffzuführung die Redoxspannung negativer, was sich positiv auf den Methanbildungsprozess auswirkt. Das Optimum der Methanerzeugung im Vergärungsprozess wird erst bei sehr negativen Redoxspannungen von etwa –350 mV bis über –500 mV beobachtet. Biogasanlagen mit einem hohen Methanbildungspotential erreichen solche Werte.
• 9. Zweckmäßigerweise erfolgt der Eintrag von Luftsauerstoff gemeinsam mit der Substratzuführung in den oberen Reaktorbereich, wo die tendenzielle Gefahr des Aufschwimmens faserreicher Biomasse am größten ist. Eine wirksame Homogenisierungstechnik führt zur gewünschten Raumverteilung im gut durchmischten Reaktor.
• 10. Zur Optimierung des Prozessablaufs ist es vorteilhaft, eine messtechnische Überwachung des Vergärungsprozesses durchzuführen, wobei insbesondere eine Überwachung folgender Parameter erfolgt: • Temperaturverhalten • pH – Wert • Äquivalente der leichtflüchtigen Fettsäuren • Bestimmung der Trockensubstanzgehalte • Erfassung der Stoffpotentiale und des C/N – Verhältnisses • Zusammensetzung und Menge des Biogases • Kontinuierliche Messung des O₂ – Gehaltes im Gärsubstrat an mindestens zwei Messpunkten • Überwachung der Redoxspannung
• 11. Die gut homogenisierbaren Gärmassen weisen eine hohe Pump- und Transportfähigkeit und eine sehr geringe Neigung zu Schwimm- und Sinkschichtenbildungen auf.

The inventive method is characterized by a number of advantages and specifics. These include in particular:

• 1. With the method according to the invention, it is possible by metered entry of oxygen to increase the reaction rate of the fermentation process. In this case, a rapid degradation of plant biomass, in particular of cellulose and hemicellulose. The degradability of the high polymer compounds can be ensured, for example, by a microbial diversity of fungi and aerobically working actinobacteria as well as anaerobic clostridia and optionally anaerobic microorganisms.
• 2. As a result of laboratory and large-scale investigations, it was verified that the introduction of atmospheric oxygen leads to accelerated degradation of cellulose-containing substrates and to organic secondary products with intercalated terminal oxygen such as alcohols, aldehydes, esters and amides, which are now more readily biodegradable , This increases the nutrient availability for the methanogenic microorganisms; the process carries turbocharacter.
• 3. In the single-stage process of methane fermentation, 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.
• 4. Although the art is uniformly believed to keep oxygen from the actual methane production process, the inventors' long-term experiments with a high-performance reactor come to the surprising conclusion that when oxygen is introduced into the reactor, it is consumed immediately and the gas formation rate increases, with simultaneous observation further negative-developing redox voltages.
• 5. 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.
• 6. The amount and duration of the entry are highly dependent on the microbiological status of the fermentation substrate pending. The entry is only useful if O ₂ - utilizing microorganisms are present there in sufficient numbers. The accompanying flora from culturally aerobic germs are fungi as well as O ₂ - consuming Gramnegative bacteria; they are crucial in optimizing biocenosis as a precursor to methanogenesis. Continuous methane formation is made possible by the presence of so-called facultative anaerobes, which can exist under short-term oxygen influences, consume them promptly and thus take over a protective function for the obligate anaerobic methane bacteria.
• 7. With periodic aeration of fermentation substrate, the original biogas rate could be increased up to a maximum of 51%. Even after repeated intake of atmospheric oxygen, biogas production was still 23% higher after more than 40 hours of experimentation compared to untreated material.
• 8. It has been proven that with the oxygen supply the redox voltage becomes more negative, which has a positive effect on the methane formation process. The optimum methane production in the fermentation process is only observed at very negative redox voltages of about -350 mV to over -500 mV. Biogas plants with a high methane formation potential reach such values.
• 9. Expediently, the entry of atmospheric oxygen takes place together with the substrate supply in the upper reactor area, where the tendency tendency of floating fiber-rich biomass is greatest. An effective homogenization technique leads to the desired space distribution in the well-mixed reactor.
• 10. In order to optimize the process, it is advantageous to carry out a metrological monitoring of the fermentation process, in particular monitoring the following parameters: temperature behavior pH value equivalences of the volatile fatty acids determination of the dry matter contents determination of the substance potentials and the C / N Ratio • Composition and quantity of biogas • Continuous measurement of the O ₂ content in the fermentation substrate at at least two measuring points • Monitoring of the redox potential
• 11. The well-homogenized gas masses have a high pumping and transportability and a very low tendency to swim and Sinkschichtenbildungen.

The Invention will be explained in more detail below with reference to an embodiment. there are those in large-scale Application with subsequent laboratory confirmation achieved Measurement results and dependencies the aerobic influence on fermentation processes shown.

In the associated Show drawing:

1 the temporal course of the periodic air intake and

2 the time dependence of the biogas rate from the air intake into the fermentation system.

In 1 is the time course of the periodic air intake, including the measured O ₂ - contents shown in the substrate. The dosage with atmospheric oxygen should be such that the inhibitory effect of oxygen with limit values of 0.1 mg / l is 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.

The respective dosage criteria of the oxygenation are, in addition to the microbiological findings, made dependent on the following measurement parameters: • O ₂ content: <0.1 mg / l • PH value: 6.5 ... 8.5 • ORP voltage: <-300 mV • Acid equivalent of volatile organic acids: <2000 mg / l • t ₁ : <20 minutes • t ₁ / t ₂ : <0.1 where t _{1 is} the Lufteintragszeit and t _{2 is} the time period between two air entries.

As a result of the aerobic treatment of the fermentation substrate higher energy densities and Faulraumbelastungen can be mastered than the scientific community allows so far. Thus, foul space loads> 7 kg oTS / m ³ _F × d are possible, without causing disruptions in the gas formation process or a markedly negative influence on the gas yield.

From the in 2 shown time dependence of the biogas rate R _B in m ³ biogas volume per m ³ _F reactor volume and days d from the air entering the fermentation system can be seen that even the untreated starting substrate shows a high gas formation rate. With the periodic air supply, the gas evolution increases explosively, drops relatively evenly in the subsequent rest phase, to continue the sequence at a slightly lower level in the follow-up. In the continuous flow fermentation process can be held relatively constant by substrate feed the set high level of gas production. The measured redox voltage shows a similar curve.

O ₂

oxygen content

t

Time

t ₁

Period of time the air entry

t ₂

Period of time between the periodic air entries

mg

milligram

mV

millivolts

l

liter

R _B

biogas rate

m ³

biogas volume (measured)

m ³ _F

reactor volume

H

hour

d

Day

kg oTS

kilogram organic dry matter

Claims (6)

Single-stage wet fermentation process for the anaerobic fermentation of liquid and / or solid manure and vegetable biomass for the purpose of generating biogas, characterized in that the fermentation substrate periodically and metered oxygen is supplied to achieve greater reaction rates. Method according to claim 1, characterized in that that the dosage of oxygen input depending on the microbiological Status of the substrate and technologically done so that an oxygen content in the fermentation substrate of 0.1 mg / l not exceeded becomes. Method according to claim 1 or 2, characterized that by the compelling presence of special facultative anaerobes in the fermentation substrate an immediate consumption of the registered oxygen takes place with the desired Follow-up effect of a splitting of cellulose and / or hemicellulose in biodegradable intermediates. Method according to one of the preceding claims, characterized characterized in that by the aerobic treatment step, a higher gas formation rate or yield from the to be fermented Biomass is achieved. Method according to one of the preceding claims, characterized characterized in that the demonstrably higher rate of degradation of Biomass a cheaper flowability this has the consequence and thus a much lower tendency to Floating and Sinkschichtenbildung has and thus higher energy densities allowed in the reactor without damaging the biogas yield. Method according to one of the preceding claims, characterized characterized in that a technological combination with others Digestion method of mechanical substrate preparation (e.g. Extrusion, intensive comminution) or enzymatic treatment of the fermentation substrate is being used.