The key to the economic viability of BGT is maximizing the use of all its outputs, not just the energy content of the gas. The slurry contains nutrients and organic material, which may be used as animal or fish food and fertilizer. The gas can be used as an energy source for pumping water and powering motors, thereby promoting small-scale village industries and generating a cash income. The sanitation effect and use of technology as a means of waste disposal and pollution abatement can also provide additional economic benefits. Thus, the potential of BGT can be realized when its place in the food-feed-fuel-sanitation system is better demonstrated.

Biogas technology is a simple technology generally utilizing waste organic materials to yield a useful fuel, methane gas. It is an indispensable source of energy in regions where the stock materials are present, and where the other conventional sources of energy are not readily available. The process of anaerobic digestion of organic materials is commonly referred to as ’biogas’ because of the biological nature of gas production. David, 1986 wrote that there is considerable interest in the use and application of biogas for several reasons. First, the escalating costs of fossil fuels and the decreasing availability of renewable sources of fuel have forced many developing countries to consider the use of renewable energy technologies (RETs) for example, solar, wind, and biomass-based technologies, such as biogas, power alcohol, and gasifiers. Of these techniques, biogas has one of the lowest financial inputs per kWh of output. In addition, biogas is one of the most ’mature’ in terms of years of use and number of units installed and has the potential to alleviate some of the more pressing problems in developing countries. (Acharya, 1958). Second, because biogas mimics natural environmental cycles, such nutrients as nitrogen, phosphorous, and potassium are conserved in the process and can be recycled back to the land in the form of slurry. This is in contrast to the burning biomass where most of the nutrients are lost, for example, with wood stoves and gasifiers. The application of slurry reduces the need for chemical fertilizers, such as urea and superphosphate, and in addition, enables humic materials to be recycled. This recycling preserves the physical properties of the soil and enables high agricultural productivity to be maintained (Maramba, 1978). Third, the biogas process digests animal manure and it has the potential to considerably reduce plant, animal, and pathogens. The cycle of reinfection is broken and considerable improvement in public health results. (Young and McCarty, 1969). Finally, because biogas is a clean-burning fuel, its domestic use can reduce the incidence of eye and lung problems that are commonly encountered with such smoke-producing fuels as firewood, agricultural residues, and coal (National Academy of Sciences. 1977). Furthermore, biogas is a versatile technology and can utilize a wide variety of organic feed stocks, such as animal manures, night soils, agricultural residues, aquatic plants, and organic industrial wastes. Hence, in addition to being a multifaceted technology, it has potential application to many environmental and social milieus (Reddy et al., 1979).