The processing of animal and human excrement in biogas systems obviously improves sanitary conditions for the plant owners, their families and the entire village community. The initial pathogenic capacity of the starting materials is greatly reduced by the fermentation process. Each new biogas system eliminates the need for one or more waste/manure/latrine pits, thereby substantially improving the hygiene conditions in the village concerned. From a medical point of view, the hygienic elimination of human excrement through the construction of latrines, connected directly to the biogas systems constitutes an important additional asset. In addition, noxious odors are avoided, because the decomposed slurry stored in such pits is odorless.
Since biogas slurry does not attract flies or other vermin, the vectors for contagious diseases, for humans and animals alike, are reduced. Furthermore, eye infections and respiratory problems, attributable to soot and smoke from the burning of dried cow dung and firewood, are mitigated.
In the rural areas of China and numerous other subtropical countries, gastrointestinal diseases are the most widespread type of affliction. Epidemics of schistosomiasis, ancylostomiasis, dysentery and others are caused by the transmission of pathogens via ova contained in fecal matter. Contagion is pre-programmed by the farmers themselves when they use night soil or liquid manure to fertilize their fields. As long as inadequate sanitary and hygienic conditions prevail, the health of the rural population will remain threatened. The anaerobic digestion of human, animal and organic wastes and effluents extensively detoxifies such material by killing most of the ova and pathogenic bacteria. It is not surprising, that the widespread popularization of biogas in China has had immediate beneficial effects on the sanitary conditions of the areas concerned. As soon as the introduction of biogas technology fully covered an area, no more human, animal or organic wastes were deposited in the open. This eliminated some of the main sources of infectious diseases. Schistosomiasis, previously a widespread, menacing disease in rural China, was reduced by 99% through the introduction of biogas technology. The number of tapeworm infections has been reduced to 13% of the pre-biogas level.
For the user of biogas technology, health effects are tangible with regards to the smoke reduction in the kitchen. The reduction of parasitic diseases can only be felt if the numbers of biogas systems in an area reaches a critical threshold. Similarly, for a larger entity like village, district or nation, health impacts of biogas systems do not grow as a linear function of the numbers of biogas units installed. Biogas subsidies can compete with expenditures for other forms of health care only, if the funds are substantial enough to reach a high coverage with biogas units.
As morbidity is, generally, a multi-factor issue, impacts of widespread biogas dissemination can only be assessed by an ex-post analysis: expenditures for the treatment of key diseases before and after the widespread introduction of biogas technology. Analyses of that kind can - with caution - be used to estimate the value of health benefits in a comparable region that is targetted for a biogas program.
The permanent availability of cooking energy in a household with a well functioning biogas plant can have effects on nutritional patterns. With easy access to energy, the number of warm meals may increase. Whole grain and beans may be cooked longer, increasing their digestibility, especially for children. Water may be boiled more regularly, thus reducing water-borne diseases.
The use of biogas for lighting can lead to profound changes in the way families integrate in the cultural and educational sectors. Biogas lighting makes it possible to engage in activities at night such as reading or attending evening courses. The women and children, of whom it was previously expected that they gather fuel, now have more free time and are more likely to attend school. Experience also shows that the use of biogas systems gives women more time to devote to the upbringing of their children.
One possible drawback of the introduction of biogas technology could be an accentuation of existing differences in family income and property holdings. Poor tenant farmers could be coerced into selling - or even delivering free of charge - their own manure supplies to the landlord or other more prosperous farmers for use in their biogas plants. Obviously, this would be of great disadvantage with respect to the already low yields and energy supplies of small and/or tenant farmers.
If the benefits of biogas technology are not to be limited to farmers with a number of livestock of above four TLUs (Tropical Livestock Units), biogas programs will have to consider biogas systems that integrate neighborhoods or villages, e.g. by building and operating community biogas systems.
The construction phase of biogas systems provides short-term employment and income due to the need for excavation, metal-work, masonry and plumbing. As documented in reports from China, the construction of biogas systems encourages local industries to manufacture the requisite building materials and accessories. Practically every district in question has its own enterprises for the production of cement, lime, bricks, plastic pipes, T-bars, plugs, stoves, lamps, gas lines, etc. Obviously, the subsequent operation and maintenance of the finished systems can have long-term beneficial effects on regional employment and income. Skilled craftsmen can be recruited not only for construction, but for service and repair. Community plants require a permanent staff for plant administration, raw material procurement, plant operation and maintenance, distribution of the gas yield and disposal of the effluent sludge.
For the poor, the main advantage of higher crop yields is that they improve the family's nutritional basis and reduce the danger of famines. The more prosperous farmers can sell their excess crops, thereby increasing their income. This has a snowball effect in that those farmers subsequently expand their mode of living and begin to spend more on such things as household appliances. Consequently, local and/or regional employment and income also benefit. However, the number of existing biogas systems has not yet become large enough to allow accurate quantification of the type and extent of the individual effects.
To the extent that the introduction of biogas technology generates jobs and higher income while improving living conditions, it may be assumed that fewer rural inhabitants will be drawn away to urban centers in search of employment. While, as mentioned above, no accurate quantification is as yet possible concerning the effects of biogas technology on rural-urban migration, most Indian experts agree that the available information indicates a real and noticeable influence. Further investigation is required for obtaining reliable data on the nature and extent of such effects.
Well functioning biogas plants can replace the entire consumption of firewood or charcoal of an individual household by biogas. In macro-economic cost-benefit analyses the amount of firewood or charcoal saved is often directly translated into hectares of forest lost. The monetary benefit of biogas would then be reflected in re-afforestation costs. This simplistic approach is questionable for four reasons:
For national or regional planning, however, the reduction of deforestation and consequent soil erosion is one of the main arguments to allocate public funds for the dissemination of biogas technology. While a ready-made formula cannot be offered to calculate the monetary value of biogas in terms of reducing deforestation, some guiding questions may assist the planner to realistically assess the profitability of biogas compared to other environmental interventions.