Accumulation of biopolymers in activated sludge biomass

In this study, activated sludge bacteria from a conventional wastewater tre atment process were induced to accumulate polyhydroxyalkanoates (PHAs) unde r different carbon-nitrogen (C:N) ratios. As the C:N ratio increased from 2 0 to 140, specific polymer yield increased to a maximum of 0.38 g of polyme r/g of dry cell mass while specific growth yield decreased. The highest ove rall polymer production yield of 0.11 g of polymer/g of carbonaceous substr ate consumed was achieved using a C:N ratio of 100. Moreover, the compositi on of polymer accumulated was dependent on the valeric acid content in the feed. Copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV) ] was produced in the presence of valeric acid. The 3-hydroxyvalerate (3HV) mole fraction in the copolymer was linearly related to valeric content in the feed, which reached a maximum of 54% when valeric acid was used as sole carbon source. When the 3HV U in the polymer increased from 0-54 mol%, the melting temperature decreased from 178 degrees to 99 degrees C. Thus, the composition, and hence the mechanical properties, of the copolymer produced from activated sludge can be controlled by adjusting the mole fraction of valeric acid in the feed medium.