In this paper, the capability of hollow-fiber membrane bioreactor (HF-MBR) for real petroleum refin- ery wastewater treatment was studied. A pilot immersed HF-MBR was designed, and the treatment investigated under various hydraulic retention time (HRT), flux, temperature, and different operational conditions. The bioreactor included an ultrafiltration membrane (UF) and Arak refinery wastewater used as the influent stream. The HF-MBR was running throughout 160 days. The result indicated that aver- age elimination efficiencies of chemical oxygen demand (COD), biological oxygen demand (BOD5 ), total suspended solids (TSS), volatile suspended solids (VSS) and turbidity were attained 82%, 89%, 98%, 99%, and 98%, respectively. Furthermore, the mixed liquor-suspended solid (MLSS) and mixed liquor volatile- suspended solids (MLVSS) concentration raised from minimal concentration to about 6.6 and 6.1 g/L, respectively.
