Treatment of volatile organic compounds in pharmaceutical wastewater using submerged aerated biological filter

Abstract

Performance of an up-flow submerged aerated biological filter (SABF), treating mixture of VOCs in pharmaceutical wastewater was evaluated. Methanol, acetone, dichloromethane, benzene and toluene were chosen as target pollutants. The effects of airflow rate, hydraulic retention time and organic loading rate on VOC emission were evaluated. During the start-up phase, SABF removed over 92% of COD, up to an organic loading rate (OLR) of 3.09±0.05kg/m3/d at 12h HRT. It was observed that the limited mass transfer of VOC to the gas phase at low air flow rate (0.4L/min, with an empty bed residence time of 114s) reduced its emission from the reactor. Performance of SABF varied with hydraulic retention time (HRT) and maximum COD removal (93%) was achieved at 10h. Reduced contact time (less than 10h) between pollutant and biomass affected the degradation of dichloromethane, benzene and toluene in the liquid phase. SABF exhibited effective degradation (95%) of VOCs up to an OLR of 17.45±0.01kg/m3/d. Enzyme inactivation reduced the efficiency (72%) of the SABF for increased OLR of 20.85±0.03kg/m3/d. Irrespective of organic loading rate, competition for the active site between the pollutants mainly affected the degradation of benzene and toluene in the liquid phase. Presence of high biomass and reduced mass transfer of VOCs to gas phase due to low air flow rate reduced VOC stripping even at higher organic loading rate. Average gas phase emission reduced to 0.075% for DCM, benzene, toluene whereas methanol and acetone was completely removed from the gas phase.