Kitchen waste and aquatic weeds are the newest sources for biogas and manure. The days of cowdung are numbered
in our country, most of the biogas plants installed are based on cowdung. In a significant departure from the usual, the Sadar Patel Renewable Energy Research Institute, Vallabh Vidyanagar, Gujarat, has developed a biogas plant which works on kitchen waste and aquatic weeds (Rural Technology, Vol 8, No 2).
Large quantities of waste accumulates, especially in community kitchens either as leftover cooked food or uncooked food like vegetable peels and rotten vegetables. Simply wasting all this proves expensive as kitchens usually use conventional fuels like liquified petroleum gas, kerosene or coal for cooking. One easy and cost-free method of disposing kitchen waste could be the installation of a biogas plant in the vicinity of a community kitchen. The fuel produced in the form of biogas could replace the consumption of conventional fuel substantially, the slurry coming out of the plant could be used as a good farmyard manure and all this could finally help maintain a clean, odour-free environment.
Agriculture Tools Research Centre, Surat, Gujarat, has developed a garbage gas manure plant (ggmp) which can be erected by local artisans for hygienically disposing garbage to produce fuel and manure. ggmp deals with all biologically decomposable soft perishable wastes. The soft organic matter is partly burnt as fuel; a part used in making farmyard manure and a good quantity is wasted. If all such wastes are decomposed through ggmp, enough biogas can be supplied to villages and cities together with organic fertilisers which can replace chemi cal fertilisers.
The complete biological decomposition of garbage in ggmp takes place in three stages -- firstly, a homogenous mixture of garbage and water is digested aerobically on an open platform for three to eight days. In the second stage anaerobic decomposition takes place in multidigesters for 25 to 50 days. Then, aerobic decomposition is carried out for about a month under shade to prepare a rich manure using earthworms.
Other important potential sources for biogas generation are aquatic weeds -- water hyacinth and salvinia. Water hyacinth is a plant which is neither used as fuel nor as fodder. It has a capacity to double itself within a short period of two to 13 days. About one kg of green water hyacinth containing 93 per cent moisture can generate 50-55 litres of biogas. For effective utilisation, hyacinth is cut into small pieces and fed into the biogas plant digester along with some water through an inlet pipe. Water and hyacinth are thoroughly mixed in a stirrer and the digested material is withdrawn from an outlet pipe. This slurry is very effective when used as manure and the gas produced is good as fuel for cooking and power generation. Gas obtained from a mixture of salvinia weeds and cowdung is double the amount from that obtained from cowdung alone. Moreover, if these weeds become the source for biogas the nuisance of weed growth can be controlled as well.
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