In this research, PHA (polyhydroxyalkanoate) production system by activated sludge was studied. PHA behaves as carbon and energy storage material in bacteria. And PHA is a biodegradable plastic when extracted from bacteria. In this paper, the investigations from 3 aspects were reported; control of PHA composition, PHA production under coexistence of nitrogenous compounds, and influence of enrichment condition on PHA productivity. As results, it was possible to regulate PHA composition by utilizing acetate and propionate as carbon source and by regulating its composition. Nitrogenous compounds did not depress PHA productivities in the case of activated sludge, while nitrogenous compounds usually depress in general. PHA contents of MLSS were achieved up to 57% by using anaerobic-aerobic activated sludge. But microaerophilic-aerobic process could supply stably the activated sludge which accumulated PHA with high efficiency.

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