The term anaerobic process refers to a diverse array of biological wastewater treatment systems from which dissolved oxygen and nitrate-N are excluded. In most instances they are operated to convert biodegradable organic matter, both soluble and particulate, to methane and carbon dioxide. Since methane is a sparingly soluble gas, most is evolved and recovered, thereby removing organic matter from the liquid phase and stabilizing any solids present in the influent or produced in the process. Anaerobic digestion of municipal wastewater solids also results in inactivation of pathogens, a step that is usually required prior to ultimate solids disposal. In some cases, anaerobic processes are operated to convert biodegradable particulate organic matter into volatile fatty acids (VFAs), which are subsequently separated from the particulate matter and fed to biological nutrient removal (BNR) systems to enhance their performance.
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