Anaerobic digestion is a process where microorganisms break down wastes in the absence of oxygen. Wastewater treatment plants utilize anaerobic digestion, post primary and secondary treatment, to stabilize remaining biodegradables from sludge. Anaerobic digestion reduces odor and bacteria levels in sludge leaving it relatively inert.1 This process can be utilized as a source of energy due to the production of biogas which consists of methane, carbon dioxide, and other trace gases. The stages of the anaerobic digestion process can be represented as such:
Stages of Anaerobic Digestion (2)
Anaerobic digesters are recognized by United Nations Development Programme as a most useful source of decentralized energy.3 In the Indian subcontinent biogas is collected in increasing popular household digestion facilities to produce “gobar gas”. Read a fascinating firsthand account of the evolving implementation of these small scale anaerobic digesters in developing countries and the resulting economic, societal, and environmental benefits. The people utilizing this innovation have the availability to utilize household waste as an energy source for cooking, lighting, and heat when no reliable power delivery infrastructure exists.
According to the American Biogas Council, in the United States there are approximately 1500 wastewater treatment plants producing biogas.4 In the United States (and other developed countries) with existing power delivery infrastructure the biogas is typically flared away. However an increasing number the larger installations are utilized to feed cogeneration systems which provide heat and electricity that can be reused at the plant or sold to a power utility.
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