The belief that energy might be a limiting factor for the development of humanity led twenty years ago to a great interest being'taken in research on anaerobic digestion. The first international symposium held in Cardiff in 1979 was followed by the meetings in Travenmund (1981), Boston (1983), Guangzhou (1985) and Bologna (1988). By now anaerobic digestion has come to be recognized as an appropriate technology for waste treatment. More recently, the increase in the carbon dioxide content of the atmosphere and (in developed countries, especially_ in the EEC) the. fact that more and more land...