Enrichment of a mixed microbial culture for PHA production with used cooking oil as substrate

The synthesis of polyhydroxyalkanoates (PHA) by a mixed microbial culture (MMC) employing used cooking oil (UCO) as substrate represents a promising bioprocess for organic wastes valorisation. In this study, MMC enrichment in a sequencing batch reactor (SBR) was investigated using UCO without pretreatment as the sole carbon source. Two SBRs (SBR1 and SBR2) were operated under a feast-famine regime with uncoupled carbon and nitrogen supply, differing in the timing of the biomass withdrawal and nutrient filling. In SBR1, with effluent withdrawal at the end of the feast phase, better poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) accumulation was achieved (average values of 4.2 ± 1.6 wt. %, maximum of 19.9 wt. %) compared to SBR2, with withdrawal at the end of the famine phase (average values of 2.7 ± 1.1 wt. %, maximum of 5.2 wt. %). The highest PHBV accumulation in SBR1 was obtained at a COD/N ratio of 46 g/g, with an active biomass concentration of approximately 1 g VSS/L. Additionally, a single UCO pulse enhanced substrate hydrolysis and consumption compared to multiple pulses. Microbial community analysis revealed the enrichment of bacterial OTUs with PHA accumulation capacity related to Azospirillum, Acinetobacter, Gordonia, Burkholderia, and Bacillus. Among fungal OTUs, Geotrichum, Meyerozyma, and Pascua were the most abundant. Multivariate statistical analysis indicated that the synergistic interaction of Burkholderia and Chitinophaga played a crucial role in achieving the highest PHBV accumulation levels.