Report of the session on biogas

In introducing the session on biogas, the Chairman, C.G. Hedén, emphasized the positive aspects of biogas technology: employment and establishment as an alternative source of energy. On the other hand, the need for more research and development on the microbiological, technological, and ecological costbenefit analyses cannot be denied. Special attention was given to the aspect of gross energy requirement, which hitherto has been glossed over in the enthusiastic implementation and promotion of biogas technology. In highlighting the areas for discussion, Hedén dealt with the energy requirements of the process, the engineering aspects (e.g., stirring), and the different types of construction and insulating materials. Integration of biogas technology into rural development schemes was another area specifically mentioned on account of the immediate, multiple associated benefits that result from such integration.

A.A. Lyamchai described the rationale behind the promotion of biogas technology, particularly in the rural areas of Tanzania. Tanzania, with an agrarian tradition, is ideally suited to use agricultural residues for the production of feed, fertilizer, and fuel as a result of biogas technology implementation.

The national programme started in 1975 following collaboration with the Khadi Village Industries Commission in Bombay, India. The experience resulting from such collaboration was described. Since then several local innovations have been tried successfully.

SIDO has technicians who provide on-the-spot training and help to get rid of bottlenecks Constraints were also emphasized, e.g., climatic considerations, lack of accessories locally, etc. A 3 m³ plant costs US$750, which is outside the reach of many rural people. Other major contraints are the cost of the installation, operation, and maintenance of biogas plants. Lack of technical experts and servicing personnel constitute a serious drawback. Various problems of digester construction and use of materials were described: an Indian design used steel for the digester, which, of course, is very expensive; a Chinese design using earth materials has been tried, which is cheap but allows leakage of effluent; and a Tanzanian design built with oil drums has proved not to be durable.

E.J. Da Silva gave a brief resume of biogas technology that has been promoted by a number of agencies. He stressed the need for integrated biogas farming systems and cited examples in the Philippines and Brazil. In addition, he also emphasized a point that has often been glossed over, viz., social acceptability and psychological prejudice to the deployment of certain resource materials. He also pointed out that the trend is now towards the use of bag digesters.

C.V. Seshadri dealt with the experiences in the laboratory versus those at on-site locations. He provided more details on the "red earth" bag that is used by Chinese scientists. The advantage of this bag is that it is UV-resistant. Seshadri stressed the importance of integration, e.g., biogas to run diesel engines and small pumps. He emphasized the fuel-food combination of the overall system. For example, fertilizer is an important constituent of the multi-component system. He reiterated the necessity of initiating appropriate measures to ensure social acceptability.

T.K. Chose provided more information on the technological aspects of biogas production. He also cited the example of a school in India that has run for a number of years on biogas produced from dung. In stressing productivity as a major problem, he highlighted some of the major bottle-necks, e.g., temperature fluctuations, choice of suitable substrates, concomitant gases occurring with CH4 generation, and efficiency of digestion of raw materials, etc.

C.G. Hedén pointed out the need for thermophilic digestion as a means of destroying pathogens.

In the discussion that followed, a number of speakers made suggestions, and both sought and provided clarifications. These were taken into consideration in the following statement.

Statement of the Working Group on Biogas

Considering the significance of rural biogas production as a means of ensuring efficient combustion in heating processes that can improve food digestibility and water safety, and also the potential of digestion to convert potentially hazardous materials into a useful nitrogen and trace-element fertilizer, the biogas group:

1. Regards biogas production as an important element in strategies to lift the levels of health and selfreliance in agricultural communities, particularly wherever large amounts of dung are generated;
2. Regards digestion as a key function within integrated bioconversion systems where it can be combined with a variety of other technologies that, in some instances, can achieve substantial synergistic effects on the level of nutrition;
3. Believes that biogas technology, applied at the village level, has not been used as it could be; it is suitable for an international effort aimed at systematic research and information exchange.

In particular, the group recommends:

1. That emphasis be given to the choice of suitable construction materials commensurate with the existing economic infrastructure (bricks, clay, etc.) in the development of simple, small-scale, rural units;
2. That systems for efficient temperature control based on solar energy and heat accumulation be developed;
3. That cheap and simple devices for stirring based on locally available resources be considered;
4. That the possibility to optimize acidification and gas production steps be studied in simple equipment, and methods to achieve stability be developed;
5. That the fate of pathogens is evaluated in the type of simple, small-scale units that might be appropriate for village use;
6. That the gas yield and productivity of various substrates and residues be studied.