Production of polyhydroxyalkanoates (PHA) by activated sludge treating municipal wastewater: effect of pH, sludge retention time (SRT), and acetate concentration in influent

In this paper, the production of biodegradable plastics polyhydroxyalkanoates (PHA) by activated sludge treating municipal wastewater was investigated. The effect of three operational factors, i.e. the acetate concentration in influent, pH, and sludge retention time (SRT) were studied. Sludge acclimatized with municipal wastewater supplemented with acetate could accumulate PHA up to 30% of sludge dry weight, while sludge acclimatized with only municipal wastewater achieved 20% of sludge dry weight. It was found that activated sludge with an SRT of 3 days possessed better PHA production capability than sludge with an SRT of 10 days. Sludge acclimatized under pH 7 and 8 conditions in sequencing batch reactors (SBRs) exhibited similar PHA production capability. However, in PHA production batch experiments, pH value influenced significantly the PHA accumulation behavior of activated sludge. When pH of batch experiments was controlled at 6 or 7, a very low PHA production was observed. The production of PHA was stimulated when pH was kept at 8 or 9.