Biological conversion processes involve enzymatic or bacterial breakdown by micro-organisms at relatively low temperatures. Methane or biogas is thus produced from plant, animal, human and industrial wastes.
The waste is fed into a specially designed digester. The microbes under the influence of low-temperature heat provided from the sun decompose the wastes and produce containing a mixture of methane, carbon dioxide, and carbon monoxide. Methane- the major component and carbon monoxide are combustible and can be used directly as gaseous fuel for cooking, heating and even for lightening purposes. It is a cheap and clean fuel and saves the trek to collect firewood and exposure to smoke in the kitchen. If latrines are attached to it then it helps village sanitation too. What makes the unit financially valuable is the cash inflow on terms of saving on firewood and production of and use of enriched manure with a high content of oxygen, phosphorous and potassium for agriculture.
The design of biogas plants in vogue in the country is mainly based on cattle dung as feedstock. Designs for night-soil based biogas plants have also been developed and extended. Waste recycling and resource recovery systems (WRRRS) are now being developed from the ongoing community/institutional and the night-soil based biogas plants.
Biogas development program is being promoted through construction of family type and community/institutional/night-soil type biogas plants. The units come in different types and sizes but some facts have to be kept in mind while setting them up. For instance, the groundwater level has to be at least 2 meters below the surface and there must be no well or hand-pump within 15 meters of it.