Different dissolved oxygen levels drive polyhydroxyalkanoate biosynthesis from hydrolyzed polyacrylamide-containing oil sludge

Hydrolyzed polyacrylamide (HPAM)-containing oil sludge is an available resource for the generation of polyhydroxyalkanoates (PHAs) by native functional microorganisms in the sludge. The impact of dissolved oxygen (DO) as an important factor on these processes is now unclear. Thus, this study established the biosystems involving the full range of DO levels involving anaerobic, anoxic and aerobic conditions by using HPAM-containing oil sludge as both substrates and microorganisms. PHAs, intermediate metabolites, extracellular polymeric substances (EPS) and microbial communities in these biosystems were determined. The associations between different PHAs and metabolites, and EPS, and functional microorganisms were explored. The PHAs produced in these biosystems included poly(3-hydroxyoctanoate-co-3-hydroxydecanoate-co-3-hydroxydodecanoate) (P(3HO-co-3HD-co-3HDD)), poly(3-hydroxydecanoate) (P(3HD)), poly(3-hydroxyoctanoate) (P(3HO)), poly(3-hydroxyvalerate) (P(3HV)) and poly(3-hydroxybutyrate) (P(3HB)). The yield of medium-chain-length (mcl)-PHAs first increased and then remained stable with DO level (0–3.5 mg·L−1). While the yield of short-chain-length (scl)-PHAs first rose and then descended and finally kept steady with DO level. Different PHA production was correlated with volatile fatty acid (VFA) generation, EPS formation and microbial function. The change trend of VFA yield was coincided with that of scl-PHA building blocks. Polysaccharides and tyrosine/tryptophan proteins in EPS were closely related to mcl-PHA biosynthesis. Pseudomonas, Bacillus, Thauera, Aeromonas and Azoarcus as the shared multifunctional bacteria dominated the biosynthesis of mcl- and scl-PHAs. Different DO levels regulated VFA generation, EPS formation and microbial function of HPAM-containing oil sludge, and consequently drove the biosynthesis of different PHAs. This study is expected to achieve a “win-win” for the environmentally friendly treatment and the resource recovery of HPAM-containing oil sludge.