Animal Waste, Water Quality and Human Health

138Animal Waste, Water Quality and Human HealthCase Study 4: Manure Management in Developing CountriesIn intensive production systems of developed countries animal waste is more likely to beconsidered a problem than a product. In contrast, developing countries typically sufferfrom a scarcity of organic fertilizer and manure is regarded as a valuable output: forexample agro-pastoralists in West Africa rank manure higher than milk in terms ofbenefits provided by cattle (Grace et al. 2009). The demand for manure in developingcountries opens the door to incentive-based methods for manure management that, asan externality or side-effect, reduce pathogen loads in manure and/or divert manureto other uses and so stop pathogen-laden faeces entering water.Using animal waste to produce biogas is an example of such an intervention. This is arelatively simple process in which gas is produced by anaerobic fermentation in sealedvessels and then under low pressure supplied to cooking stoves: “free” fuel is of course amajor incentive for farm households for whom energy for cooking is an important part ofthe household budget. An additional benefit is the digestant which is odourless andhighly valued as a fertiliser. Moreover, biogas is more efficient than cattle dung fueland contributes less to greenhouse gases, and cooking with biogas results in muchless exposure of women and children to particulate matter which is a major cause ofdisease. At the same time, anaerobic digestion will reduce most pathogens by morethan 99% and thus can be considered an effective strategy for rendering animal wastesafe; biogas, therefore, offers the basis for a win-win solution providing botheconomic benefits and mitigation of zoonotic hazards.Of course, things are not always so simple and this case study summarises thehistorical development of biogas use in India to draw lessons for the introduction ofmanure management technology. Biogas (called “gobar gas” in India, as nearly allcomes from cows) was first used in 1897; however, it was not widely promoted untilthe energy crisis of the 1970s. Early models were technically efficient but had anumber of disadvantages including: high cost of parts which had to be brought fromoutside the village, use of milled steel gas holders which required annual painting toremain rust free, and dependence on a high level of masonry skills for building andrepair. As with many transferred technologies, the challenge proved not to beinstalling plants but rather maintaining them, and as much as 80% of these firstgeneration units fell into disuse.Realization of these problems led to the development of simpler and moreappropriate models and the increasing involvement of non-governmentalorganizations in delivery. Units currently used are much simpler and can beconstructed with materials available in the locality; using the waste of four head ofcattle a farmer can get enough cooking gas to meet the needs of a household of six toeight people. The biogas installation programme is subsidized by the Government ofIndia and targets have been established for each state; at present around 200,000 peryear are being constructed and most are found to be working on follow-up visits. Yet,despite these impressive results, biogas still has a very minor role in supplying the