Comparison of two PAC/UF processes for the removal of micropollutants from wastewater treatment plant effluent: process performance and removal efficiency.

Two hybrid membrane processes combining powdered activated carbon (PAC) adsorption with ultrafiltration (UF) were investigated regarding operational performance and efficiency to remove organic micropollutants from municipal wastewater treatment plant effluent. A pressurized PAC/UF (pPAC/UF) and a submerged PAC/UF (sPAK/UF) system were operated continuously over a period of six months. Both UF membrane systems showed good compatibility with the application of PAC showing no abrasion or other negative impacts. The pPAC/UF system reached permeability values up to 290 L/(m² h bar) at high fluxes of 80 L/(m² h) compared to the sPAC/UF with a permeability of up to 200 L/(m² h bar) at fluxes of up to 23 L/(m² h). Surface analysis of both membranes with scanning electron microscopy revealed no membrane deterioration after the six-month period of operation. On the surface of the pressurized membrane the formation of a PAC layer was observed, which may have contributed to the high permeability by forming a protective coating. Five micropollutants, i.e. sulfamethoxazole, carbamazepine, mecoprop, diclofenac and benzotriazole in ambient effluent concentrations were investigated. Both PAC/UF systems removed 60-95% of the selected micropollutants at a dosage of 20 mg PAC/L and 4 mg Fe(3+)/L. However, extreme peak loads of sulfamethoxazole with concentrations of up to 30 μg/L caused a considerable performance decrease for more than a week.