Biogasis a term used to describe a mixture of gases containing mostly Methane (CH4)(50 – 70 %), and some of other gases like Carbon dioxide (CO2) (30 –40 %), Hydrogen (H2), and Hydrogen Sulphide (H2S) produced bymicrobial activity which may beused as fossil fuel and natural gas substitute. During growth certain microbescan produce certain gases as waste of their metabolism, the gas produceddepends on the type of microbes and what organic matter digested by them.
For exampleat the making of kombucha, Acetobacter xylinum is used to ferment teawhich will produce CO2 as metabolism waste of digesting sugar,however certain anaerobic bacteria which can be found in cellulosic materialcan produce asignificant amount of methane. Bacteria with this trait are classified asMethanogens, a common example for methanogens is Methenobacterium which can befound in cow’s rumen or in sewage sludges, but before the organic matters canbe metabolized by these Methanobacterium, it has to go through several processes involving digestion of organic matter byHydrolitic bacteria, Acidogens, and Acetogens to make it suitable forMethanogenesis.Hydrolitic bateria is a group of bacteria that playone of the most important role in biogas production.
Hydrolitic bacteria catabolisecomplex polymers inside organic matters into simpler monomer, making it easierfor other group of bacteria to digest it., this kind of bacteria is commoninside digestive system, that is why biogas is usually made from organic matteroriginating from manure or sewage instead of other wastes since it is moreeffective. Based on book written byPrakash S. B. (2012), Organic matters in use are generally composed of complex polymers suchas lipids, proteins, cellulose, hemicelullose and lignin, these complexpolymers have to be broken down into simpler soluble monomers by catabolizing itwith the help of water to help the digestion of organic matter,enzymes and facultative anaerobic bacteria such as Cellulomonas sp, Eubacteria sp, Clostridium sp, and Ruminococcus sp, which are usually be found inside cow’sdigstion system or in sewage sludge,these bacteria turns the organic matter into aslurry composed of simpler soluble monomers, this processtakes place inside an anaerobic bioreactor or digester which the organic matteris sterilized at 70 oC to kill pathogenic microorganisms and thencooled inside with temperature of 35 – 38 oC for optimal mesophilicenvironment or 52 oC for optimal thermophilic environment. Accordingto Yuni Erlita this process starts roughly in the first 8 day in traditionalin-home bioreactor and the gas produced are mainly Carbon Dioxide (CO2),which should be thrown away.Simple monomers formed during hydrolisis then must be digested by another group of bacteria namedAcidogens changing them into acids and carbon dioxide, this group of bacteriais also commonly found inside manure or sewage waste making it easy to find.Said process is also crucial in biogas production because the quantity of acidproduced will diectly affects the quantity of biogas end product.
According onbook written by Prakash S. B (2012), Acidogenesis process utilizes acid-producingfacultative anaerobic bacteria such as Escheriacoli, Clostridium sp, Actinomyces sp, and Corynebacterium sp, turning thesoluble monomers in the slurry into acids such as, Hydrogen (H2),Carbon Dioxide (CO2), Ammonia (NH3),Hydrogen Sulphide (H2S), shorter fatty acids, carbonic acids, alcohols, as well as traceof other byproducts, this process is called Acidogenesis, according to YuniErlita, this process occurs at the same time and environment of Hydrolysis, anddone by bacteria classified as Acidogens. The next bacteria involved in biogas production is Acetogens,this bacteria will digest the acids produced by Acidogens in the previous processand turn them into acetate. Acetate is one of the most important substanceproduced by microbe in biogas production. Said substance is the one that willbe turned into methane in the last stage of biogas production.
Based on bookwritten by Paul Singleton and Diana Sainsbury (2006), before Methanoges canproduce methane, it has to went into digestion that turns derivative of carbons, and other energy source matters fromacidogenesis into Acetic Acid (CH3COOH), some traces Carbon Dioxide (CO2), and Hydrogen(H2) which is synthesized by Acetogens autotrophically, for exampleAcetobacter woodii which synthesize necessary products which will be digestedand used by Methanoges to synthesize methane needed to make biogas. Accordingto Prakash S. B. (2012), All the microbe involved in biogas production, includingAcidogens live in optimal pH of 6.
5 – 8 which is a slightly lower than neutralor basic solution.The last stage of biogas production is Methanogenesis, which means a synthesization ofmethane. Methanogenesis is done by methanogens through its digestion of acetate,hydrogen, and carbon dioxide which will produce methane. Methanogens are alsocommonly present in manure and sewage waste, which is why people mainly usemanure as the main organic matter to produce biogas.
According to Thauer and Shima (2006),Methanogens are a group of anaerobic microorganism that produce a significantamount of Methane (CH4) and other gasses as metabolic byproduct, the exampleof Methanogens are Methanobacterium sp., and Methanococcus sp., they liveinside cattle’s digestive system. Methanogens can easily digest aceticacid (CH3COOH), and produce Methane (CH4) and a trace of Carbon dioxide (CO2),Methanogens then will digest Carbon dioxide (CO2) and Hydrogen (H2), producing Methane(CH4) and Water (H2O).According to IPCC, 1 Kilogram manure can produce 0.24 m3per kilogram or roughly 250 gram Methane (CH4)(50 – 70 %), with traces ofother gases like Carbon dioxide (CO2) (30 – 40 %), Hydrogen (H2),and Hydrogen sulphide(H2S) (20% – 30%) overa 24 hour period of time, this result depends on microbial activity, drymatter, organic matter, and time.