ABSTRACT
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References .......................................................................................................................... 489
Environmental engineers have been using biological processes for the treatment of municipal
wastewaters and sludges for over a century [1, 2]. Processes such as activated sludge and
trickling filters are used to remove organic compounds from municipal wastewaters prior to
discharge into receiving waters. Anaerobic digestion is used to stabilize municipal sludges,
converting particulate organic matter into methane and carbon dioxide. Biological processes
are increasingly used to reduce the nutrient content of wastewaters, primarily inorganic
nitrogen and phosphorus, to prevent eutrophication (loosely defined as the overgrowth of
algae and green plants), and dissolved oxygen depletion in receiving waters. In these processes,
enzymes contained in bacteria catalyze a series of reactions that hopefully transform pollutants
into less hazardous or environmentally benign products. In the case of biological phosphorus
removal, the offending phosphorus is sequestered by bacteria and removed from the liquid
stream by sedimentation prior to discharge. More recently, environmental engineers have
applied biological processes to clean up (‘‘remediate’’) contaminated waters, soils, and air.
The term bioremediation is commonly used to describe this application of biological treatment.
