Synthesis of polyhydroxyalkanoates (PHA) from excess activated sludge

This study focused on the polyhydroxyalkanoates (PHA) synthesis from excess activated sludge (EAS), from a laboratory-scale sequencing batch reactor (SBR) or a full-scale municipal wastewater treatment plant (MWWTP), via monitoring and controlling the dissolved oxygen (DO) of the cultural media through an oxidation-reduction potential (ORP) setup.; When Carbon-even numbered fatty acids such as acetate and butyrate was used as sole carbon source respectively, PHB homopolymer or PHA with dominant 3HB unit was synthesized. Otherwise, Poly-(3-hydrobutyrate-co-3-hydroxyvalerate) (PHBV) copolymer with 3HV major unit was synthesized when C-odd numbered fatty acids, propionate and valerate, were used as sole carbon sources. The minimum PHA content at ORP -30mV was about 12% (w/w) of cell dry weight where acetate was carbon source. The maximum PHA content of 35% (w/w) was obtained when ORP was +30mV. When ORP was maintained at +30mV and propionate as carbon source, the 3HV molar fraction in PHBV copolymer was 78.0 mole%. Decreasing of ORP from +100mV to -30 mV, equivalent to decreasing the DO concentration, resulted in the variation of 3HV mole fraction i n the PHA copolymer either a cetate or propionate as carbon sources.; EAS from full-scale MWWTP was conducted for the PHA production from glucose, 3HV unit content in the PHBV increased from 11.1 mol% to 78.4 mol% with the decreasing of ORP from +10mV to -20mV. It was believed that an unknown metabolic mechanism for 3HV synthesis in PHBV has been found by using the ORP setup for processing controlling instead of DO meter, which provided more sensitive, reliable and precise controlling.; A hypothetic metabolic model by using glucose as sole carbon source for PHA synthesis from EAS was proposed. It is postulated that TCA cycle and glyoxylate pathway are involved in the PHA accumulation even under anoxic and anaerobic conditions. Oxygen in this model is the key exogenous factor for the controlling of 3HV molar fraction in PHBV.