Efficient polyhydroxyalkanoates production by anoxic mixed microbial cultures in two-stage sequencing batch reactors: conceptual validation and microbial insights

Abstract

Single-stage microbial production of polyhydroxyalkanoates (PHA) requests concurrent microbial selection, biomass maintenance, and intracellular polymer storage within the same unit, thereby hindering the attainment of high-level PHA storage. Two-stage sequencing batch reactors (SBRs), designated as A-SBR and B-SBR, were established to develop efficient PHA production by mixed microbial cultures (MMC). Our results showed that A-SBR had developed a continuous biomass with a stable PHA storage capacity of 31.1±6.4%, with a maximum PHA content of 44.3%. On this basis, B-SBR achieved efficient PHA storage of 63.2±10.7% during the steady state with a peak value of 86.8%, with continuously receiving the PHA-storing biomass from A-SBR. Correspondingly, the PHA yields of A-SBR and B-SBR were 0.2±0.1 and 0.5±0.1 g COD_PHA/g COD, respectively. Notably, B-SBR achieved a peak PHA yield of 0.8 g COD_PHA/g COD, promising its superior PHA production potency. The 16S rRNA gene amplicon sequencing revealed that the two-stage SBRs developed rich and distinct PHA-producing populations, which together occupied 37.9%−54.9% and 33.6%−62.3% of the total microbial populations in A-SBR and B-SBR, respectively. Notably, Allobrachymonas and Paracoccus dominated in A-SBR, and Paracoccus, Allobrachymonas, and Thauera dominated in B-SBR. Prediction of microbial functional profiles further validated the dominance of enzymes essential for PHA biosynthesis. This study was the first to validate the high efficiency of MMC-based anoxic PHA production in a two-stage SBR configuration, which promises high rate PHA production in a cost-saving manner owing to the anoxic operation mode and thus encourages further efforts on the development of MMC-based two-stage anoxic PHA production.