Accumulation of Biopolymers in Activated Sludge Biomass

Abstract

In this study, activated sludge bacteria from a conventional wastewater treatment process were induced to accumulate polyhydroxyalkanoates (PHAs) under different carbon-nitrogen (C:N) ratios. As the C:N ratio increased from 20 to 140, specific polymer yield increased to a maximum of 0.38 g of polymer/g of dry cell mass while specific growth yield decreased. The highest overall polymer production yield of 0.11 g of polymer/g of carbonaceous substrate consumed was achieved using a C:N ratio of 100. Moreover, the composition 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.