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This volume in the Energy from Wastes Series covers the area of methane production from agricultural and domestic wastes. Principally this involves the conversion of excreta and other organic effluents to a valuable gaseous fuel plus, in many cases, a useful sludge for fertiliser or feedstuffs. Dr Hobson and his colleagues have written a comprehensive text on the principles of microbiological processes and the biochemistry of anaerobic digestion, embracing the design of digesters with examples of current working installations. The potential for anaerobic digestion of wastes as diverse as sewage to fruit processing effluents is also reviewed. This work should be of interest to all who have to manage organic waste treatment and disposal, as well as to a wider readership who wish to know more about methane production by anaerobic digestion. ANDREW PORTEOUS v Preface The production of methane, or more exactly, a flammable 'biogas' containing methane and carbon dioxide, by microbiological methods ('anaerobic digestion') is not new. The reactions have been in industrial use for over a hundred years, but only in sewage purification processes. In some times of national stress, such as war-time, the microbiological production of gas purely for fuel has been investigated, but with the resumption of plentiful su pplies of fossil fuels the investigations have faded awa y.
Table des matières
1 Introduction.- 2 Methods of production of fuels from biomass.- Physical and physico-chemical methods.- Biological methods.- 3 The microbiology and biochemistry of anaerobic digestion.- The microbial population in general.- The breakdown of carbohydrates.- The breakdown of nitrogenous compounds.- The breakdown of fats.- Minor bacterial reactions.- Methane production.- Factors affecting the rates of growth and activities of digester bacteria and interactions amongst the bacteria.- Conclusions.- 4 Types of digesters: theoretical aspects and modelling of digester systems and deviations from theory.- Biological models.- The Engineering Model.- The Economic Model.- 5 Types of digesters being constructed and the operation of digesters.- Starting a digestion.- The single-stage stirred-tank digester.- The contact digester.- Anaerobic filters.- The upflow sludge-blanket digester.- The fluidised-bed digester.- Digesters for agricultural wastes and vegetable matter.- Gas-holders and gas handling.- Safety precautions and tests with digesters.- 6 Uses of digested sludge.- Use as fertiliser.- Use in animal feedstuffs.- 7 Biogas production-laboratory and pilot-plant experiments.- General-the apparatus.- Domestic sewage.- Domestic garbage.- Industrial wastes.- Agricultural wastes.- Conclusions.- 8 Energy production by practical-scale digesters.- Domestic and municipal sewage.- Domestic garbage with sewage sludge.- Other wastes.- Appendix 1 Photographs of full-scale working digesters.- Appendix 2 Some estimates of wastes available for biogas or other fuel production.- Appendix 3 Glossary of terms.
