Production of polyhydroxyalkanoates (PHA) from aerobic granules of refinery sludge and Micrococcus aloeverae strain SG002 cultivated in oily wastewater
This study investigates on accumulation of polyhydroxyalkanoates (PHA) biopolymers in aerobic granules having mixed sludge and pure strain inoculum while treating oily wastewater in aerobic granular reactors (AGRs). AGR operation improved granule size (4.51 ± 0.13 mm), volatile suspended solids (VSS: 7.54 ± 0.16 g/L) and extracellular polymeric substances content (EPS: 409.36 ± 1 mg/g VSS) with 90 ± 1% chemical oxygen demand (COD) and hydrocarbon removal in refinery sludge granules. Small sized (0.71 ± 0.04 mm) Micrococcus aloeverae strain SG002 granules achieved 81.40 ± 0.2% hydrocarbon removal efficiency accumulating 0.47 ± 0.01 mg PHA/mg cell dry weight (CDW) due to cocci populated strong microbial structure. Changing organic loading (0.6–1.8 kg COD/m3. day) and high C/N (8–24) stimulated 0.71 ± 0.04 mg PHA/mg CDW yield in the refinery granules. Long and short chain n-alkanes (C16–C36, C6–C10) were mostly transformed into PHA and nondegraded fractions remained in AGR effluents. About 40–70% PHA was accumulated in feast phase which was mostly utilized for microbial metabolism in famine phase. PHA yield per unit COD removal ranged between 0.38 to 0.89 mg PHA/mg COD. PHA production proportionally increased with EPS concentrations. Granule extracted PHA was characterized as co-polymer P (3HB-co-3HV) having 3.5–4.5 of butyrates to valerates (PHB:PHV) ratios. Hence, the study provides a simultaneous process of oil removal and bioplastic production with environmental impacts.