Making dung cakes, West Bengal

Credits: © Nancy Durrell McKenna / Panos Pictures

This Indian woman is one of millions of villagers who collect and make dung cakes for fuel. But many others can now use all their waste organic material to create a smokeless biogas fuel - and have a residue left over for use as fertiliser.

By putting materials such as cow dung, human waste and vegetable matter into an airtight concrete tank, where bacteria slowly digest, it is possible to produce a gas which is roughly 60 per cent methane and 40 per cent carbon dioxide. This is then piped to the house to be used directly for cooking and heating, or to run electricity generators. Despite its origins, the gas is completely clean, odourless and atmospherically friendly - it keeps carbon dioxide emissions neutral and emits no sulphur. Cooking with clean-burning gas, rather than smoky wood, improves respiratory health and reduces pressure on fuelwood and saves women an average of 3 hours every day not having to forage for wood. Even the sludge that comes out at the end makes an excellent enriched fertiliser.

A National Project on Biogas Development was started as early as 1982 to promote household biogas plants to provide a clean and cheap source of energy in rural areas. Currently, there are around 2.5 million household and community biogas plants though the Indian government estimated that 12 million could be usefully installed. Together these plants have generated fuel gas equivalent to some 7.5 million tonnes of firewood, valued at $90 million a year. Besides, these plants produce about 35 million tonnes of organic manure per year. But biogas is taking off in many other parts of India. In towns and cities where waste is available in bulk quantities, biogas production plants can operate on a much bigger scale. At the Pumjee Paper Mills in Poona, they have incorporated biogas into their production processes, to cut back on their energy bills and pollution. The factory's biogas plant uses wastes from the pulping process and provides 15 per cent of power requirements. Many Indian companies, among them chocolate manufacturers and distillers, are following suit.

An added bonus is that the effluents used to make biogas are broken down in the process, making the resulting waste water easier to treat. In addition, if this technology can be extended to operate with human waste from public toilets in smaller towns and larger villages, it will reduce the risks of contamination and improve hygiene considerably.

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