MICROBES IN PRODUCTION OF BIOGAS

Biogas is a mixture of gases produced from degradable organic matter by activity of various anaerobic bacteria.

The microorganisms involved in biogas production are mainly facultative as well as strict anaerobic bacteria.

The most important among them are methanogenic archaebacteria, represented by Methanobacterium.

The other bacteria involved are Bacillus, Cellulomonas, Clostridium and Ruminococcus.

These bacteria are commonly found in anaerobic sludge formed during sewage treatment. Methanogens do occur in rumen of cattle where they act upon cellulose.

Composition of biogas :

The major component of biogas is methane (about 50 —70%) which is highly inflammable. The other gases are carbon dioxide (30 — 40%) and 10% mixture of other gases, viz., H2, H2S etc. Calorific value of biogas is 4429 kcal/m3 at 50% methane content.

Substrates Useful in Biogas Production :

Commercial Production of Biogas :

The technology for biogas production was developed in India by IARI (Indian Agriculture Research Institute) and KVIC (Khadi and Village Industries Commission).

A biogas plant has a large (10-15 ft. deep) concrete or brick lined air tight cylindrical tank called digester.

It has a charge pit for passage of slurry into digester, a floating gas holder of metal with an outlet for gas and a pit for removal of sludge or manure. The raw material used in biogas plants is cattle dung, night soil, farm refuse, water weeds (e.g., Eichhornia) and other organic wastes.

It is converted into slurry with 90% water content and fed to digester.

Cattle dung contains Methanobacterium and other methanogens which are normally present in rumen of cattle for aiding in digestion of cellulose.

An inoculum can also be provided when a gobar gas plant is to be initiated.

Formation of biogas is a three step anaerobic process :

1. Solubilisation (Decomposition) :

Organic wastes are composed of lipids, proteins, cellulose, hemicellulose and lignin. In the first stage of biogas generation, facultative anaerobic decomposers are active.

They secrete hydrolytic enzymes, e.g., lipases, cellulases, proteases, peptidases.

The enzymes breakdown the complex organic components into simpler and soluble substances. The latter are commonly called monomers.

2. Acidogenesis :

Monomers are changed into organic acids with the help of fermentating microbes. The most common organic acids produced during acidogenesis is acetic acid.

Hydrogen and carbon dioxide are produced as by products.

3. Methanogenesis :

Methanogens or methane producing bacteria become active.

They act on various components of microbial digestion and fermentation. Some important basic reactions are :