Mixed-culture polyhydroxyalkanoate (PHA) production integrated into a food-industry effluent biological treatment: A pilot-scale evaluation

Abstract

Production of a mixed microbial culture (MMC) biomass for polyhydroxyalkanoate (PHA) production was integrated into the wastewater treatment (WWT) of a potato-starch factory. A pilot-scale on-site evaluation was conducted over ten months, with inherent water quality variations including organic composition, temperature, and pH. The wastewater was rich in acetate and the organic matter content fluctuated from 50 to 90 % with respect to volatile fatty acids (VFAs). The PHA accumulation potential (PAP) of the surplus biomass, nevertheless, remained from 0.40 to 0.70 gPHA/gVSS. Biomass PAP characteristics were benchmarked at both pilot and laboratory scales using different feedstocks and accumulation methods. The resultant co-polymer type could be readily shifted by changes in feedstock VFA content. Selected polymer batches were recovered at pilot scale as commercial-quality prototype materials for development of PHA-based wood-fibre composites. WWT performance with 98 % organic contaminant removal remained consistent throughout. The good settleability of the pilot-scale biomass was in contrast to the poorly settleable biomass from the factory’s full-scale activated sludge. Metered nitrogen and phosphorus addition ensured stable WWT without major nitrification levels. Successful robust outcomes of both feast-famine selection principles and WWT can be translated and integrated into the full-scale WWT by a proposed adaptation to existing infrastructure. Analogous aerobic feast enrichment is proposed to be achievable with continuous or intermittent flow through a process selector/zone. This pilot-scale experience under actual field conditions of industrial WWT provides further evidence for the technical viability to produce biomass for PHA production while maintaining standards in effluent water quality.