BIOGAS, an asset to rural India for fuel can also provide water and manure from the plant's slurry. The biogas plant utilises animal dung and water to produce high quality gas and slurry, which can serve as an excellent manure. But since this slurry is very dilute (94-95 per cent moisture) its storage, usage and handling becomes difficult. Therefore, the slurry requires to be processed to separate and recover both water and manure from the slurry for easy handling (Changing Villages, Vol 15, No 1-2).

Filter beds were designed by Indian Agricultural Research Institute and the Centre of Science of Villages, Wardha, but this experiment was unsuccessful since it resulted in free flow of slurry rather than separating water from it. This dewatering study was carried out on a gobar bio-gas plant at Anand, Gujarat. Various types of vegetation such as matured rice straw, fresh neem leaves and green leaves in different amounts were tried. These experiments suggested that some critical factors, which need to be identified, were involved in its separation.

It was decided that a filter bed at least four cm thick should be prepared using only succulents, that is, soft leafy water storing plants and small leaves instead of sticks and twigs to make the mixed filter bed into a relatively dense strainer.

Two masonary tanks of 100