Among the factors that determine the practical and economic feasibility of biogas production in a developing country, either as a waste management option or as an energy resource, or both, two are particularly important: 1) availability of the required technology, and 2) the extent of the country's economic resources. However, superseding the two factors is magnitude of the proposed undertaking. The decisive influence of magnitude arises from the fact that technological and economic requirements escalate almost logarithmically with increase in magnitude, and soon exceed available technological and financial resources of all but the more highly industrialised countries.
Table XI-7. Enteric pathogens
Category Disease Organisms (where identified)
Viral Infectious hepatitis Gastroenteritis Respiratory illness Poliomyelitis adenovirus reovirus enterovirus (poliovirus) Bacterial Typhoid fever
Salmonellosis Bacillary dysentery Cholera Tuberculosis Salmonella typhosa Salmonella spp.
(Exp. S. paratyphi, S. schottmueleri)
Shigella spp. (Shiegellosis) Vibrio cholerae
Mycobacterium tuberculosis
Protozoan Amebiasis Entamoeba histolytica
(Amebic dysentery) Helminthic (Roundworm) (Pinworm) (Whipworm) (Tapeworm) (Hookworm) Ascaris lumbricoides Oxyaris vermicularis Trichurus trichiura Taenia saginate Ancylostoma duodenale Necator americanus
Table XI-8. Survival of pathogens in the anaerobic digestion process Organisms Temperature (°C) Residence Time (days)a Die-Off (%) Poliovirus 35 2 98.5 Salmonella ssp. 22 to 37 6 to 20 82 to 96 Salmonella typhosa 22 to 37 6 99 Mycobacterium tuberculosis 30 100 Ascaris 29 15 90 Parasite cysts 30 10 100b Sources: References 28-30. a Time in digester. b
Does not include Ascaris.
An arbitrary but logical and convenient classification of “magnitude” is into “large-scale” and “small-scale”. Accordingly, a large-scale operation is one that involves 100 Mg or more per day,
and serves a metropolitan area. The primary function of a large-scale plant is the treatment of wastewater solids (sewage sludge), and biogas production is secondary and coincidental. Small- scale operations are suited to villages and individual farms, or to groups of farms. In operations on that scale, biogas production ranks with waste treatment in terms of priority.
J1. LARGE-SCALE undertakings
As of this writing, the record of large-scale biogas installations, other than conventional wastewater solids treatment, is singularly scarce and unimpressive in developing countries. Available technology for non-sewage sludge, large-scale operations based on low-solids digestion has not been successful, largely because of operational problems and deficiencies in digester design and construction. Currently, the trend is toward high-solids digestion. However, the largest high-solids digester presently in operation is modest in size. It is only relatively recently that some European designs have been applied to the anaerobic digestion of primarily manures and the highly putrescible fraction of domestic waste. A photograph of a new high-solids anaerobic digester is shown in Figure XI-9. The facility is in Salzburg, Austria and processes on the order of 18,000 Mg/yr. The digested residue is dewatered and composted in tunnel reactors. A portion of the gas produced by the digester is used to generate electricity for use by the facility. The remainder of the gas is burned in a flare. Digesters of this type operate under the following conditions: digester loading, 10 to 30 kg of COD/m3 of digester volume-day; temperature, 50° to 58°C; and a detention time of 15 to 30 days. Based on these conditions, one could expect a production of about 4 to 8 Nm3 of biogas/m3 of digester volume per day, with a concentration of methane of about 60% (by volume) [24]. Several of these and similar units have been installed in primarily Western European countries.
Courtesy: CalRecovery, Inc.
Figure XI-9. Example of high-solids anaerobic digester J2. SMALL-SCALE undertakings
Technical problems encountered in small-scale operations generally are related to maintenance and functioning of the digester [10]. Examples are corrosion of gas holders, “wear and tear” of components such as the guide pipe of the gas holder and of hoses, and the development of cracks in the digester walls. Financial constraints arise mainly from the relatively high costs of construction materials, scarcity of land on which to locate the plant, and diversion of labour to unrelated activities. In some countries, sociological and cultural problems may be manifested by a prejudice against connecting latrines to a gas plant, or in a reluctance of farmers to use a latrine [10]. The problems are aggravated by the low levels of gas production that occur during cold weather.
Problems that beset small-scale farm operations can be alleviated through integration into a community installation. The integration would be accompanied by the establishment of an organisational program designed to: 1) provide follow-up service; 2) ensure frequent contacts with relevant agencies for technical advice; and 3) establish a mechanism for access to reliable and regular supply of raw materials and plant components, and provide for personal contacts by biogas technicians.
K. References
1. American Public Health Association (APHA), Standard Methods for the Examination of
Water and Wastewater, APHA, 13th Ed., New York, New York, USA, 1971.
2. Anonymous, Anaerobic Digestion of Dairy Cow Manure at the State Reformatory Honor Farm, Monroe, Washington, Ecotope Group and Parametrix, Inc., Sumner, Washington, USA, 1975.
3. Chan, D.B. and E.A. Pearson, Comprehensive Studies of Solid Waste Management:
Hydrolysis Rate of Cellulose in Anaerobic Fermentation, SERL Report No. 70-3, Sanitary
Engineering Research Laboratory, University of California, Berkeley, California, USA, October 1970.
4. Fry, L.J. and R. Merrill, Methane Digester for Fuel, Gas, and Fertilizer, Newsletter No. 3, Santa Cruz, California: New Alchemy Institute-West, USA, 1973.
5. Gotaas, H.B., Composting, World Health Organization Monograph Series, No. 31, WHO, Geneva, Switzerland, 1956.
6. Hayes, T.D., W.J. Jewell, J.A. Chandler, S. Dell'Orto, K.J. Farfoni, A.P. Leuschner, and D.F. Sherman, “Methane Generation from Small Scale Farms”, Biogas and Alcohol Fuels
Production, proceedings of a seminar on Biomass Energy for City, Farm, and Industry,
Chicago, Illinois, JG Press, Emmaus, Pennsylvania, USA, May 1979.
7. Leeper, G.W., Managing the Heavy Metals, Pollution Engineering Technology Series, Marcel Dekker, Inc., New York, New York, USA, and Basel, Switzerland, 1978.
8. McGarry, M. and J. Stainforth, editors, Compost, Fertilizer, and Biogas Production from
Human and Farm Wastes in the People's Republic of China, International Development
Research Centre, Ottawa, Ontario, Canada, 1978.
9. National Academy of Sciences (NAS), Methane Generation from Human, Animal, and
Agricultural Wastes, Report of an Ad Hoc Panel of the Advisory Committee on Technology
Innovation, National Research Council, NAS, Washington, DC, USA, 1977.
10. Prakasam, T.B.S., “Application of Biomass Technology in India”, Biogas and Alcohol Fuels
Production, proceedings of a seminar on Biomass Energy for City, Farm, and Industry,
Chicago, Illinois, J.G. Press, Inc., Emmaus, Pennsylvania, USA, May 1979.
11. Singh, R., Bio-gas Plant: Generating Methane from Organic Wastes, Gobar Gas Research Station, Ajitmal, Etawah (V.P.) India, 1971.
12. Singh, R., “Building a Bio-Gas Plant”, Compost Science, 13(2):12-17, March/April 1972. 13. Singh, R., “The Bio-Gas Plant -- Generating Methane from Organic Waste”, Compost
Science, 13(1):20-26, January/February 1972.
14. Sullivan, J.L., C.M. Ostrovski, and N. Peters, Feasibility Analysis Model for Centralized
Methane Production from Animal Wastes, Report for Ontario Ministry of Energy (File No.
1903-02-876-24) Faculty of Engineering Science, The University of Western Ontario, London, Canada, 1978.
15. Hungate, R.E., “Studies on Cellulose Fermentation - I. The Culture and Physiology of an Anerobic Cellulose Digesting Bacterium”, Journal of Bacteriology, 48:499-513, 1944. 16. Hungate, R.E., “The Anaerobic Mesophilic Cellulytic Bacteria”, Bacteriological Review,
14:1-49, 1950.
17. Hungate, R.E., “Microorganisms in the Rumen of Cattle Fed a Constant Ration”, Canadian
Journal of Microbiology, 3:289-311, 1957.
18. Madden, R.H., M.J. Bryder, and N.J. Poole, “Isolation and Characterization of an Anaerobic Cellulytic Bacterium, Clostridium papyrosolvens sp. nov.”, International Journal of
Systematic Bacteriology, 32:87-91, 1982.
19. Madden R.H., “Isolation and Characterization of Clostridium stercorarium sp. nov. Cellulitic Thermophile”, International Journal of Systematic Bacteriology, 33:837-840, 1983. 20. Mendez, B.S., M.J. Pettinari, S.E. Ivanier, C.A. Ramos, and F. Sineriz, “Clostridium
thermopapyrolyticum sp nov., a cellulolytic thermophile”, International Journal of Systematic Bacteriology, 41:281-283, 1991.
21. Zeikus, J.G., “Microbial populations in digesters”, Anaerobic Digestion, D.A. Stafford, B.I. Wheatley, and D.E. Hughes (ed), 61-89 pp., Applied Science Publishers, London, England, 1980.
22. Kaseng, K., K. Ibrahim, S.V. Paneerselvam, and R.S. Hassan, “Extracellular Enzymes and Acidogen Profiles of a Laboratory-Scale Two-Phase Anaerobic Digestion System”, Process
Biochem., 27:43-47, 1992.
23. Diaz, L.F., G.M. Savage, G.J. Trezek, and C.G. Golueke, “Biogasification of Municipal Solid Wastes”, Journal of Energy Resources Technology, 103:180-185, June 1981.
24. Personal Communication, City of Salzburg, Austria, October 1995.
25. European Council, “Council Directive 1999/31/EC of 26 April 1999 on the landfilling of waste”, Official Journal of the European Communities, L 182, 1-13; 1999.
26. Diaz, L.F., et al., “Selective Aspects of the Treatment of Biodegradable Waste in the European Union”, presented at the 2002 International Symposium on Composting and Compost Utilization, Columbus, Ohio, USA, May 2002.
27. Kayhanian, M. and S. Hardy, “The Impact of Four Design Parameters on the Performance of a High-Solids Anaerobic Digestion of Municipal Solid Waste for Fuel Gas Production”,
Environmental Technology, 15(6):557-567, 1994.
28. Bertucci, J., et al., “Inactivation of Viruses During Anaerobic Sludge Digestion”, Journal of
Water Pollution Control Federation, 49(7):1642-1651, 1977.
29. Foster, D.H. and R.S. Engelbrecht, “Microbial Hazards in Disposing of Wastewater and Soil”, Recycling Treated Municipal Wastewater and Sludge through Forest and Cropland, W.E. Sopper and L.T. Kurdos, eds., Pennsylvania State University Press, University Park, Pennsylvania, 1973.
294
30. Dotson, G.K., “Some Constraints of Sprading Sewage Sludge on Croplands”, Land Disposal
of Municipal Effluents and Sludges, Proceedings of Conference on Land Disposal of
Municipal Effluents and Sludge, March 1972, U.S. Environmental Protection Agency, EPA- 902/9-73-001, 1973.