Filamentous organism bulking in nutrient removal activated sludge systems: Paper 9: Review of biochemistry of heterotrophic respiratory metabolism

Abstract

Biochemical mechanisms for respiration by facultative organisms are reviewed in two sequential parts. In Part I, the biochemical reactions involved in the utilisation of substrate under aerobic and under anoxic conditions are outlined. In Part II, the mechanisms which initiate, regulate, and terminate respiration under each of aerobic and anoxic conditions are described. A consequence of Part II is identification of a series of conditions and mechanisms in which one of the intermediates of denitrification (nitrite, or nitric oxide) interacts with the aerobic respiratory enzymes (the cytochrome oxidases), resulting in inhibited aerobic respiration when organisms are alternately exposed to anoxic and aerobic conditions. This mechanism is an important aspect of a conceptual biochemical model for facultative heterotrophic organisms developed in Paper 10 (Casey et al., 1999a).

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