Many developing countries are encouraging for the installation of biogas plants to meet out the demand of fuel. India is one of the pioneer countries in biogas technology. U.P. Government in the years 1957 and 1960 established a permanent station named ‘Gobar gas Research Station’ at Ajitmal in Etawah district.
There are many other institutions where research and development programmes are earned out such as Khadi and Village Industries Commission (KVIC), Bombay, the Gram Vikas Sansthan, Lucknow and National Environmental Engineering Research Institute, Nagpur.
The Non- conventional Energy Development Agency (NEDA) of Uttar Pradesh has already installed several night soil-based biogas plants throughout the state.
One of the major plants installed at Kanpur is the Rajapurwa Biogas Plant where about 1400 kg human waste from 50 seat toilet complex is pooled through underground pipelines at one place. The waste is processed through a digester into about 55 m3 methane gas.
This quantity is enough to run an 8 HP engine and pump-set and to provide fuel to some biogas lamps and cooking burners to about 3500 dwellers. The sewage plant at Okhla (New Delhi) has 15 digesters of 5665 m3 capacity each, and produces 17,000 m3 gas per day which is equivalent to about 10,000 litres kerosene per day.
National sugar Institute, Kanpur has developed methods for production of biogas from bagasse and other agricultural residues. It is estimated that five catties generate dung to produce 2 m3 biogas plants to meet the demand of cooking and lighting for a family of 4-5 people. Biogas and H2 based engines are successfully developed.
Benefits from Biogas Plants:
In Asia, biogas is used mainly for cooking and lighting purposes. In addition, there are many other advantages in installing the biogas plants. It is used in internal combustion engines to power pumps and electric generators. Sludge is used as fertilizer. The most economical benefits are minimising environmental pollution and meeting the demand of energy for various purposes.
Feedstock Materials:
There are two sources of biomass i.e. plant and animal for biogas production. The biomass obtained from plants is aquatic or terrestrial in origin, while biomass generated from animals includes cattle dung manure from poultry, goat, sheep and slaughter houses, fisheries waste, etc.
Cattle dung is most potent for biogas production. Besides dung (gobar), agricultural residue, apple pomade and deteriorated or dumped wheat grains are also proved to be good source for biogas production.
Biogas Production (Anaerobic Digestion):
The anaerobic digestion is carried out in an air tight cylindrical tanks which is called digester. A digester is made up of concrete bricks and cement or steel. It has a side opening (charge pit) into which organic materials for digestion are incorporated.
There lies a cylindrical container above the digester to collect the gas. A diagram of single stage digester for gobar gas plant is shown in Fig. 33.2. It is noticed that after 50 days, sufficient gas is produced in gas tank, which is used for house hold purposes. Usually, digesters are burned in soil in order to benefit from insulation provided by soil. In cold climate, digester can be heated.
Metabolic activities of methanogens are quite peculiar. Carbon dioxide fixation, Calvin cycle, serine or hexulose pathways are absent in them.
Several coenzymes such as methyl coenzymes M, hydroxymethyl coenzyme M, coenzyme F420, coenzyme F430, component B, methanofuran or carbon dioxide reducing factor, methanopterin and formaldehyde activating factors are present.
The primary reaction in which carbon dioxide formation occurs is given below.
CO + H2O → CO2 + H2
The secondary reaction takes place in the presence of sufficient hydrogen.
CO2 + 4H2 → CH4 + 2H2O
Other reactions showing methane formation from various substrates are given below:
4CH3OH → 3CH4 + CO2 + 2H2O
4HCOOH → CH4 + 3CO2 + 2H2O
CH3COOH → 12CH4 + 12CO2