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  • Title: Production of polyhydroxyalkanoates in open, mixed cultures from a waste sludge stream containing high levels of soluble organics, nitrogen and phosphorus.
    Author: Morgan-Sagastume F, Karlsson A, Johansson P, Pratt S, Boon N, Lant P, Werker A.
    Journal: Water Res; 2010 Oct; 44(18):5196-211. PubMed ID: 20638096.
    Abstract:
    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 COD(sol) 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 COD(VFA) 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 (T(d) = 283-287 °C) and a molecular mass ranging from 0.7 to 1.0 × 10(6) 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 COD(sol) 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.
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