Biogas is a combustible gas mixture consisting of 50 ÷ 70 % of methane (CH4), which is formed of organic compounds in the process of anaerobic microbiological process. Also biogas composition includes 30 ÷ 40% of carbon dioxide (CO2) and small amounts of hydrogen sulphide (H2S), ammonia ( NH3) , hydrogen (H2) and carbon monoxide (CO). Prodution of biogas from the organic substances on an industrial scale, mainly from the organic wastes, is based on the controlled process of decomposition of organic matter in the anaerobic, i.e. anoxic conditions. Biogas production technology can be divided into four phases:
Hydrolysis phase. During the course of the hydrolysis phase, resistant substances (such as proteins, fats and carbohydrates) are decomposed into simple components (such as amino acids, glucose, fat acids), in the result of bacterial activity.
Acid-forming phase. Simple components formed during the hydrolysis phase are decomposed into the organic acids (such as acetic , propionic , butyric), alcohole , alcohol oxide, hydrogen, carbon dioxide, and such gases as ammonia and hydrogen sulfide. This process proceeds up until the development of bacteria slows down under the influence of the formed acids.
Acidogenic phase. Under the influence of acidogenic bacteria, formed of acids during acid-forming phase, acetic acid is produced.
Methanogenesis. Acetic acid is decomposed into methane, carbon dioxide and water.
Key parameters of the biogas production.
Anoxic conditions. Bacteria can actively operate only in the conditions of oxygen absence. Compliance with this condition was initially provided in the construction of a biogas unit by biogas plant manufacturers.
Humidity. Biogas production is realized only in a wet environment because only there bacteria can live, feed, breed and produce biogas.
Temperature. The optimal conditions for all groups of bacteria range from 35 to 40C. The automatic control system.
Fermentation period. The amount of the gas produced is gradually increased as duration of fermentation increases. At the beginning it is faster, and with increasing duration of fermentation - more slowly. There comes a moment when it is not appropriate from an economic point of view to contain that in a fermenter. Our experts use a scientific approach and possess many years' experience in the calculation of the effective stay period in the reactor.
pH. Hydrolysis and acid forming bacteria in acidic medium with pH level of 4,5-6,3 reach its optimum activity. Acetic acid and methane forming bacteria can only survive at neutral or weakly alkaline pH level of 6,8-8. The following rule operates for all bacteria: if the pH level exceeds the optimal one, the bacterial activity is slower, which slows down the formation of biogas. The optimal pH level for the bacterial activity and methane formation equals 7.
Substrate supply. Metabolic products of each group of bacteria are the nutrients for the next group of bacteria. They all operate at different speeds. Bacteria cannot be "overfed" because one of the groups will not have enough time to make food for the next group. Therefore, frequency of the substrate supply is calculated and programmed in each of the projects.
Feed preparation. The size of bacteria is 1/1000mm. The smaller the particles of the substrate are, the greater the contacting area with the bacteria. As a result the fermentation period will be reduced, and the methane formation increased. For the purpose, when necessary, further substrates refinement is undertaken, prior to forwarding it into fermenter.
Shuffle. It is important for not only prevention of crustand sediment, but also for drawing off the generated gas (helps gas bubbles to rise on the surface).
Process stability. Microorganisms are used to a certain "diet". Changes should be made gradually.
It’s necessary to avoid insertion of such elements asantibiotics, disinfectants and chemicals, acids and large quantities of heavy metals into fermenter.