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

Biochemical mechanisms for respiration by facultative organisms are reviewe d 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 termina te respiration under each of aerobic and anoxic conditions are described. A consequence of Part II is identification of a series of conditions and mec hanisms in which one of the intermediates of denitrification (nitrite,or ni tric oxide) interacts with the aerobic respiratory enzymes (the cytochrome oxidases), resulting in inhibited aerobic respiration when organisms are al ternately exposed to anoxic and aerobic conditions. This mechanism is an im portant aspect of a conceptual biochemical model for facultative heterotrop hic organisms developed in Paper 10 (Casey et at, 1999a).