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Studies on the metabolism of polyhydroxyalkanoic acid and phosphate in the biological excess phosphate removal process Wu, Manhong


The basic objectives of my thesis were to examine the role of PHA in phosphate sequestering sludge metabolism and to test the effect of nutrient combinations on the intracellular level of PHA. The role of PHA in the process was studied by measuring levels of PHA in both functional and non-functional sewage treatment plant conditions. The role of nutrients was studied by testing the effects on PHA of nutrient combinations which would be expected to affect the level of NADH. Despite previous correlation between PHA storage and phosphate sequestering, it was found that even with good PHA storage in the anaerobic condition some sludges showed poor phosphate uptake in the corresponding aerobic condition. PHA accumulation requires NADH and is dependent on a proper NADH and NAD balance in the cells. However, most biochemical studies have been limited to pure components such as acetate which have limited capacity to generate NADH under anaerobic conditions. Thus this study focused on nutrient combinations which would provide a suitable carbon source as well as proper reducing equivalent balance. Several nutrient combinations were tested including the fermentation products pyruvate, butyrate and ethanol. Fluoroacetate was used as an inhibitor of the glyoxylate cycle. It seemed that the glyoxylate cycle was not the only source of NADH for PHA synthesis.

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