Valorization of highly saline pickle brine waste into polyhydroxyalkaonate by mixed microbial culture

Sustainable and cost-effective polyhydroxyalkaonate (PHA) production could be achieved with integration of using renewable substrates derived from waste feedstock and mixed microbial culture (MMC). This study aimed to investigate the PHA production capacity of highly saline pickle brine waste (PBW). In this context, the impact of sludge retention time (SRT) on enrichment of PHA storing MMC capable of using highly saline PBW and its effect on microbial community structure was studied. Sequencing batch reactors (SBRs) were operated at SRTs of 2, 4 and 6 days using raw PBW. Feast/famine ratios in all SBRs were between 0.03 and 0.09 indicating high PHA- storage capacity at salinity of 14.8 g NaCl/L. Highest PHA productivity was achieved at SRT of 6 days with PHA storage yield of 0.79 g COD-PHA/g COD and PHA content of 74 % (wt). Microbial population analyses revealed that PHA-producer halotolerant Neomegalonema spp. dominated the total biomass with 41 % in SBR-6 whereas halotolerant PHA-storing Paracoccus spp. and Rhodobacter spp. were dominant in SBR-4 and SBR-2. PBW is suggested to be a favorable feedstock as enrichment of halotolerant PHA storing MMC with stable and high PHA productivity was achieved which would be promising for full-scale applications.