Scale up of PHA production in a single-unit system with used cooking oil and a mixed microbial culture

The production of polyhydroxyalkanoates (PHAs) using mixed microbial cultures (MMC) and waste as substrate, like used cooking oil (UCO), represents an innovative approach to reduce operational costs while valorising these residues. However, the main challenge when using oily substrates lies in the competition between PHA- and triacylglyceride- (TAG) storing populations, which can hinder high PHA production yields. In the present study, the feasibility of PHA synthesis with a MMC and UCO as substrate is evaluated at pilot-scale in a single-unit system (R1), where culture enrichment and PHA accumulation take place. Percentages of PHA accumulated inside the cells of 40 wt. % were achieved, while those of TAG remained at values of approximately 10 wt. %, indicating successful enrichment of PHA-storing populations. To further assess the potential of the enriched MMC, an additional accumulation unit (R2) was implemented downstream of R1. In R2, the enriched culture showed a capacity to synthesise PHA to values as high as 60 wt. %. Even so, the productivity in the single-unit reached a higher value (0.019 g PHA/(g UCO·h)) than that obtained in the two-unit system (R1 + R2) (0.013 g PHA/(g UCO·h)). These findings highlight the potential of a simplified single-unit process, serving as basis for a future industrialization.