High and tailored long-term accumulation of PHA enabled by a versatile mixed microbial culture

Abstract

Polyhydroxyalkanoates (PHAs), such as poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) copolymers, are biopolymers that can serve as substitutes for conventional plastics as they have similar properties. The objective of this study was to develop a robust mixed microbial culture (MMC) enriched in microorganisms capable of accumulating high intracellular PHBV content. The MMC was successfully enriched and operated stably over the long term (521 days) in a sequencing batch reactor (SBR) in which the carbon and nitrogen feeding were uncoupled. Its maximum PHBV accumulation capacity and biopolymer production yield were 62 wt% and 0.59 CmolPHBV/CmolVFA, respectively, and treated OLRs of up to 6 g COD/(L⋅d), which influenced the microbial community composition. The maximal accumulation capacity of the MMC, evaluated in batch experiments, was 83 wt% PHBV and yields of 0.63 CmolPHBV/CmolVFA. Similar results were obtained with the two synthetic volatile fatty acid (VFA) compositions tested. When the potential of this culture to use pre-acidified (VFA-rich) wastewater from fish canning residues as a substrate was evaluated, the highest obtained values were 56 wt% PHBV and 0.36 CmolPHBV/CmolVFA. The results demonstrate that PHBV composition can be adjusted by VFA feed composition (either synthetic or residual), highlighting the process versatility.