Role of a halothermophilic bacterial consortium for the biodegradation of PAHs and the treatment of petroleum wastewater at extreme conditions

•94% COD removal by treating petroleum wastewater in continuous stirred tank reactor.•Complete degradation of PAHs in petroleum wastewater under extremophilic condition.•Consortium degraded 86% phenanthrene at 20% salinity, survived till 30% salinity.•Ochrobactrum is dominant extremely halophilic strain in the consortium.

Petroleum hydrocarbons are major pollutants in marine environments. The present study describes the potential of a halothermophilic bacterial consortium capable of degrading polycyclic aromatic hydrocarbons (PAHs) in petroleum wastewater under extreme conditions. The consortium was enriched from brine originating from a desalination plant. The consortium efficiently degraded both the low molecular weight (LMW) PAHs-naphthalene (NAP), phenanthrene (PHN), anthracene (AN) and fluorene (FLU) as well as the high molecular weight (HMW) PAHs-pyrene (PY), benzo(e)pyrene (B(e)P) and benzo(k)fluoranthene (B(k)F), respectively. A nearly quantitative release of carbon dioxide (85 ± 1.2%) in conjunction with significant reduction of PAH concentration and an increase in bacterial cell count (from 104 to 109 cfu/mL) pointed at mineralization of PHN. The consortium was able degrade 86± 2.7% and 58± 4.1% of PHN (200 ppm) at 20% and 30% NaCl concentration respectively. Co-metabolism with PHN thereby enhanced the degradation of HMW PAHs. In petroleum refinery wastewater the PAHs were potently degraded by the bacterial consortium with 94 ± 3.8% COD removal in a continuous stirred tank reactor. Ochrobactrum halosaudia strain AJH1, Ochrobactrum halosaudia strain AJH2 and Pseudomonas aeruginosa strain AJH3 were present in the PAH-degrading halothermophilic consortium.