Enhanced biological treatment of a residual oil processing plant wastewater by a membrane-bioreactor for effluent quality improvement in a Hungarian refinery

Abstract

A 160-day-long preliminary laboratory scale MBR treatment study and the performance test of a new 480 m3/day capacity full scale plant for quality improvement of effluent from a bitumen plant off-gas scrubbing followed by dissolved air flotation were conducted. Two testing periods were distinguished during the laboratory study, specifically the first with 100 days SRT and the second with 50 days SRT. To evaluate the possibility of the organic matter removal enhancement at the end of each testing period powdered activated carbon (PAC) treatment was carried out. The COD and oil & grease removal efficiency of the well acclimated MBR sludge was greater than 90% and 98%, respectively. The COD content of the treated wastewater during the full scale performance test period was reduced below 100 mg·L−1. To ensure an optimal treatment process, the organic loading rate should be kept in 1.5 – 3 kg COD m−3 d−1 range. and optimal biomass concentration of 10-15 g·L−1 should be ensured to reduce the cleaning frequency of the membrane ultrafilters. To avoid exceedance of compliance with respect to the discharge criteria, further treatment step(s) should be considered prior to any treated wastewater reuse.