Waste Activated Sludge as Biomass for Production of Commercial-Grade Polyhydroxyalkanoate (PHA)

Purpose This paper presents an assessment of the production of polyhydroxyalkanoates (PHA) in biomass sourced from wastewater treatment plants (WWTPs). The purpose was to examine both the potential for more generic utilization of waste activated sludge as biomass for PHA production and the quality of the polymers produced. Methods Biomass was sourced from two full-scale WWTPs. A refined acetic and propionic acid feedstock was used to produce a P(3HB-co-3HV) (polyhydroxy-butyrate-valerate or PHBV) copolymer in a single-stage from this biomass as-received. Results The mean overall storage yield was 0.25 +/- 0.03 gCOD of polymer per gCOD feedstock consumed. The average PHA cell content was 0.26 +/- 0.08 gPHA gVSS(-1). Microstructure and thermal properties analysis showed that the polymers produced were most likely a mixture of random copolymers, with polymer composition being mainly a function of substrate composition. The PHA recovered was of high purity and exhibited thermal characteristics similar to published values. Conclusions Based on published data, the overall yield for a conventional PHA production system, utilizing volatile fatty acid (VFA) feedstocks for biomass and biopolymer production, is 0.19 gPHA per gVFA(COD), which is similar to that obtained in this work. In other words, efficiency of VFA feedstock utilization is similar. Considering activated sludge biomass is abundantly available around the world, this work suggests that industrial scale PHA production could be achieved more generally in conjunction with sludge management rather than using purpose specific biorefineries where biomass is grown on high value feedstocks.