Handbook of Biogas Technology
About this eBook
Preface To feed ever-increasing human population we have to grow more food from given area of land. Industrial growth is also necessary for development of nation. The agricultural, industrial and household kitchen, hotels etc. sectors generates huge amount of wastes whose management is becoming a serious problem today. Environmental pollution is increasing day by day due to these wastes. Landfilling, composting, incineration etc are the most common technologies adopted for management of these wastes but biogas technology would be the most prominent one for it. In this technology wastes are degraded anaerobically through microorganisms. Simultaneouly, biogas and digested slurry are produced. The technology is quite simple and requires digester unit which holds the waste material and provides anaerobic environment. Many types of digesters have been developed each having its own advantages and disadvantages. Use of a particular type of digester depends on a number of factors including nature of waste to be degraded, its composition, cost and availability of construction material, prevailing environmental conditions in the area etc. Biogas is a mixture of gases and contains methane 50 to 70 , carbon dioxide 30 to 40 , hydrogen 5 to 10 , nitrogen 1 to 2 , water vapors 0.3 and hydrogen sulphide traces . It can be used for cooking and lightning purposes to run the water lifting pumps to generate energy and electricity and as vehicle fuel but before this it requires purification. Purification means removal of all unwanted gases from biogas except methane. For it a number of techniques are available today. Besides biogas the second by product of biogas digester i.e. digested slurry also have a number of uses due to its high nutrients content. It can be used as feed for earthworms, carps, fishes or microorganisms. Its well known use is as fertilizer which gives increased crop yield with better quality. Application of biogas slurry to soil also improves its fertility and productivity. Biogas technology is an economically sound technology conditioned that the biogas and digested slurry are being managed with high skill. It requires one time investment of construction of biogas digester which operates successfully for a longer period of more than decade. Biogas technology is the best source of employment generation especially in rural areas. Biogas digester have highly diverged microbial communities due to which a number of waste materials can be used for production of biogas. The
5 composition, pH, salinity and toxicity of compounds present in waste materials affects the biomethanation process. Microorganisms are quite sensitive to change in these parameters from their normal acceptable values. Any deviation from normal range may result in decreased biogas production or in extreme cases biogas production may cease. Practically it is quite difficult to maintain all of these factors within the functional limits of microorganisms but nowadays these changes may be monitored on-line using many instruments. Certain compounds are being successfully used as additive to increase biogas production. Biogas potential of waste material depends on its accessibility to microorganisms of digester. Easy microbial accessibility will increase biogas production. The accessibility can be increased by physical, chemical, microbial or enzymatic treatment of waste material before its addition to digester.