Popular about biogas. Scheme, description

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Popular about biogas. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Alternative energy sources

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Obtaining biogas from organic waste is based on their properties to release combustible gas as a result of the so-called "methane fermentation" in anaerobic (without air) conditions. The biogas produced by methane digestion is a mixture of 50-80% methane, 20-50% carbon dioxide, approximately 1% hydrogen sulfide, and minor amounts of some other gases (nitrogen, oxygen, hydrogen, ammonia, carbon monoxide and etc.). Recall that 1 m2 of methane during combustion releases energy equal to approximately 20-25 MJ.

In turn, "methane fermentation" occurs during the decomposition of organic substances as a result of the vital activity of two main groups of microorganisms. One group of microorganisms, usually called acid-forming bacteria, or fermentative microorganisms, breaks down complex organic compounds (fiber, proteins, fats, etc.) into simpler ones, while primary fermentation products appear in the fermented medium - volatile fatty acids, lower alcohols, hydrogen, carbon monoxide, acetic and formic acids, etc. These less complex organic substances are a source of nutrition for the second group of bacteria - methane-producing bacteria, which convert organic acids into the required methane, as well as carbon dioxide, etc.

This complex complex of transformations involves a great variety of microorganisms, according to some sources - up to a thousand species, but the main ones are still matane-forming bacteria. It should be noted that they multiply much more slowly and are more sensitive to environmental changes than acid-forming fermenting microorganisms, therefore, at first, volatile acids accumulate in the fermented medium, and the first stage of methane fermentation is called acidic. Then the rates of formation and processing of acids are aligned, so that in the future the decomposition of the substrate and the formation of gas proceed simultaneously. And of course, the intensity of gas release depends on the conditions that are created for the life of methane-forming bacteria.

Both acid-forming and methane-producing bacteria are found ubiquitously in nature, in particular in animal excrement. It is believed that cattle manure contains a complete set of microorganisms necessary for its fermentation. And this is confirmed by the fact that the process of methane formation is constantly going on in the rumen and intestines of ruminants. Therefore, it is not necessary to use pure cultures of methane-producing bacteria for biogas production in order to induce the fermentation process. It is enough to provide the bacteria already in the substrate with suitable conditions for their vital activity.

To create such conditions, organic waste is fermented in special fermentation chambers (bioreactors), where a strictly anaerobic environment is maintained, as well as appropriate temperature and acid (pH) conditions, pressure, etc.

And now, before proceeding to the consideration of various designs of biogas plants, let us briefly dwell on the main factors affecting the efficiency of such plants. Knowing these factors will make the bio-installation truly profitable and will not turn the work of obtaining much-needed gas into useless shoveling of manure!

Plants for the production of biogas from landfill are generally divided into four main types:

without heat supply and without mixing of fermented biomass:
without heat supply, but with mixing of the fermented mass;
with heat supply and biomass mixing;
with heat supply, with biomass mixing and with means of control and management of the digestion process.

It is clear that the mandatory components of a biogas plant - the bioreactor itself and the gas tank for collecting biogas, but the devices for heating the biomass, mixing it, as well as control devices - are very useful things, but you can do without them.

Author: Shomin A.A.

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