Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
4484709 | Water Research | 2010 | 16 Pages |
In this study, the production of polyhydroxyalkanoates (PHAs) from waste activated sludge (WAS) was evaluated. PHAs were produced from fermented WAS pretreated via high-pressure thermal hydrolysis, a stream characterised by high levels of nutrients (approximately 3.5 g N L−1 and 0.5 g P L−1) and soluble organics. PHA-storing organisms were successfully enriched at high organic loading rates (6 g CODsol L−1 d−1) under aerobic dynamic feeding in sequencing batch reactors at a sludge retention time of 6 d with a short feast length less than 20% of the cycle, and a maximum substrate concentration during feast of 1 g CODVFA L−1. The biomass enrichment, characterised by a decrease in species evenness based on Lorenz curves, provided a biomass that accumulated 25% PHA on a dry-biomass basis with yields on VFA of 0.4 Cmol Cmol−1 in batch tests. The PHA consisted of ∼70 mol% 3-hydroxybutyrate and ∼30 mol% 3-hydroxyvalerate, and presented high thermal stability (Td = 283–287 °C) and a molecular mass ranging from 0.7 to 1.0 × 106 g mol−1. Overall PHA storage was comparable to that achieved with other complex substrates; however, lower PHA storage rates (0.04–0.05 Cmol PHA−1 Cmol X−1 h−1) and productivities (3–4 Cmol PHA L−1 h−1) were probably associated with a biomass-growth and high-respiration response induced by high levels of non-VFA organics (40–50% of CODsol in feed) and nutrients. PHA production is feasible from pretreated WAS, but the enrichment and accumulation process require further optimisation. A milder WAS pretreatment yielding lower levels of non-VFA organics and readily available nutrients may be more amenable for improved performance.