Recycling and reuse of human excreta for biogas generation is an important way to get rid of health hazards from human excreta. Sulabh is the pioneering organization in the field of biogas generation from public toilet complexes. After a series of experiments, the organisation developed a more efficient design of biogas plant that has been approved by the Ministry of Non-conventional.
Energy Sources, Govt. of India, for its implementation through state nodal agencies. Human excreta contain a full spectrum of pathogens. Most of these pathogens are eliminated due to anaerobic condition inside the digester. Besides using biogas for different purposes, biogas plant effluent can also be used as manure or discharged safely into any river or water body without causing pollution. Thus biogas technology from human wastes has multiple benefits – sanitation, bioenergy and manure.
Based on the ‘Sulabh Model’ design, 200 biogas plants of 35 to 60 cum capacity have been constructed by Sulabh in different states of the country so far. Human excreta based biogas technology remained unnoticed for long due to the fact that the available technology was not socially acceptable, as it required manual handling of human excreta, which contains a full spectrum of pathogens. The design developed by Sulabh does not require manual handling of human excreta and there is complete recycling and resource recovery from the wastes. The Digester is built underground into which excreta from public toilets flows under gravity. Inside the digester biogas is produced due to anaerobic fermentation by the help of methanogenic bacteria. The biogas, thus produced, is stored in inbuilt liquid displacement chamber. One cubic foot biogas is produced from the human excreta of per person per day. Human excreta based biogas contains 65-66% methane, 32-34% carbon dioxide and, rest the hydrogen sulphide and other gases in traces.
Methane is the only combustible constituent, which is utilized in different forms of energy. Its calorific value is 24 MJ/cum or about 5000 Kcal/cum. A one thousand cft. (30 cum) of biogas is equivalent to 600 cft. of natural gas, 6.4 gallons of butane, 5.2 gallons of gasoline or 4.6 gallons of diesel oil. Biogas is utilized for cooking, lighting through mantle lamps, electricity generation and body warming during winter. Cooking is the most efficient use of biogas. Biogas burners are available in a wide ranging capacity from 8 cft to 100 cft biogas consumption per hour. It burns with a blue flame and without soot and odour. The biogas mantle lamp consumes 2-3 cft per hour having illumination capacity equivalent to 40 W electric bulbs at 220 volt. Motive power can be generated by using biogas in dual fuel internal combustion (IC) engine. Air mixed with biogas is aspirated into the engine and the mixture is then compressed, raising its temperature to about 350°C, which is the self-ignition temperature of diesel. Biogas has a high (600°C) ignition temperature. Therefore, in order to initiate combustion of the charge, a small quantity of diesel is injected into the cylinder just before the end of compression. The charge is thus ignited and the process is continued smoothly.
At optimum condition only 20% diesel is required, rest (80%) is substituted by biogas. Biogas consumption by engine is 15 cft/BHP/hour. A public convenience used by about 2000 persons per day would produce approximately 60 cum of biogas which can run a 10 KVA genset for 8 hours a day, producing 65 units of power. Sulabh has developed a novel technology to run dual fuel genset on biogas alone i.e. without any diesel. Under the system ignition of compressed biogas is done through battery operated spark system. It is a new method to make biogas based electricity generation sustainable.
Human excreta based biogas system has multiple advantages; improves sanitation, makes availability energy, bio fertilizer and reduces green-house effect.