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 represent a promising bioprocess for organic wastes valorisation. In the present research work, the effect of sequencing batch reactor (SBR) operational strategy on MMC enrichment and PHA accumulation was investigated using UCO without pretreatment as the sole carbon source. Two enrichment 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-R-hydroxybutyrate-co-3-R-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, highlighting the importance of feeding composition as a key operational control parameter. Additionally, a single UCO pulse resulted in more efficient substrate hydrolysis and consumption than multiple pulses in both systems. Microbial community analysis revealed the enrichment of bacterial OTUs related to Azospirillum , Acinetobacter , Gordonia , Burkholderia , and Bacillus , as well as fungal OTUs such as Geotrichum , Meyerozyma , and Pascua . Multivariate statistical analysis indicated that the synergistic interaction of Burkholderia and Chitinophaga played a crucial role in achieving the highest PHA accumulation levels.