Treatment of petroleum refinery effluents by a hybrid system of activated sludge and rotation biological reactor, followed by the sand filter

In this study, a novel hybrid treatment system was designed to increase the removal efficiency of petroleum refinery wastewater. The hybrid system is a pilot scale including an activated sludge combined with a rotating biological contractor (RBC) and sand filter. Four vertical rotating polyurethane disks in the aeration tank combined activated sludge-rotating biological contactor pilot. The influent wastewater for this system was the effluent from the DAF unit in the Shahid Tondgooyan Oil Refining Co's wastewater treatment plant. The rotation rate of disks and retention time has been evaluated for their impact on the removal efficiency of total dissolved solids (TDS), dissolved oxygen (DO), pH, total suspended solids (TSS), turbidity (TU), chemical oxygen demand (COD), biochemical oxygen demand (BOD), ammonia (NH3). According to the results, enhancing the rotational speed of disks (from 4 rpm to 8 rpm) and increasing the retention time (from 6 hours to 10 hours) can improve COD, NH3, TSS, BOD5, TU, TDS, and oil removal efficiency of this system to 100, 98.52, 84.21, 100, 99.25, 13.32 and 100% respectively. Escalating the rotational speed beyond 8 rpm had reverse effects on the performance of this hybrid system. The rotational speed of 8 rpm and a retention time of 10 hours were the optimum conditions for removing the abovementioned parameters. It is worth mentioning that the high TU removal efficiency of the system was due to the presence of a sand filter. This system performed well in removing pollutants compared to other biological wastewater treatment systems.