An alternative anaerobic treatment process for treatment of heavy oil refinery wastewater containing polar organics

•UASB showed a good performance on treatment of heavy oil refinery wastewater.•Refractory polar organics were degraded and biodegradability was improved.•Granular sludge with an average particle size of 1 mm was formed.•Organic loading rate was much higher than current anaerobic tank.

Heavy oil is an important part of energy sources, but the refining wastewater is difficult to treat by the conventional anaerobic process, which has low efficiency and poor ability to resist impact load. In this study, an up-flow anaerobic sludge bed (UASB) reactor was applied to treat heavy oil refinery wastewater containing large amounts of polar organics. Through a progressive increase of hydraulic conditions, the average removal efficiencies of COD and total oil reached 70% and 72%, respectively, at an organic loading rate (OLR) of 3.44 kg COD/m3 d. GC–MS analysis revealed that more biodegradable organic acids and alcohols were generated and macromolecular polar organics were degraded into small molecular intermediates after UASB treatment. The morphology observation of the sludge demonstrated that granular sludge with an average particle size of 1 mm was formed. Moreover, the predominant species and microbial community shift could reflect the performance of the reactor. The long-term operation of UASB exhibited excellent polar organic removal efficiency. The study demonstrated the potential of UASB as an alternative for high-efficiency anaerobic treatment of heavy oil refinery wastewater.