Continuous cultivation strategy for yeast industrial wastewater-based polyhydroxyalkanoate production

Polyhydroxyalkanoates (PHAs) present an eco-friendly alternative for conventional plastics. Industrial wastewater from the food industry is a copious source of organic carbon that can be recovered in the form of PHA. However, the wastewater composition varies considerably among the different industries demanding for an industry-specific investigation of the PHA production process. Wastewater from the yeast industry, besides its high concentration in organic carbon, also contains a high ammonium concentration which might decrease the PHA production. Thus, this study aims to investigate PHA production using yeast industry wastewater via an enriched mixed microbial culture (MMC). A less explored cultivation strategy, i.e., continuous cultivation for PHA production was evaluated and compared to the widely used batch cultivation. PHA accumulating MMC was enriched using a sequencing batch reactor (SBR) operated under aerobic dynamic feeding. An MMC dominated by the Thauera species was successfully enriched in the SBR. Experimental results showed that ammonium is indeed required for PHA accumulation and the complete absence of ammonium negatively affects the accumulation process. Using wastewater, batch and continuous feeding strategies, respectively, yielded the PHA accumulation of 72 % and 65 % per dry cell weight. Despite the slightly lower PHA accumulation with continuous cultivation, four times more biomass growth was produced. Consequently, higher theoretical PHA production (270 t/year) can be expected using continuous cultivation in half of the reactor volume (45 m³). Therefore, this study asserts the viability of continuous cultivation as a feasible investigatory tool and PHA production strategy.