Submerged microfiltration-catalysis hybrid reactor treatment: Photocatalytic inactivation of bacteria in secondary wastewater effluent

Abstract

Abstract This study investigated the performance of a membrane photocatalytic reactor (MPR) with respect to the removal of bacteria from secondary effluents. The MPR achieved disinfection through several mechanisms: rejection by a membrane, inactivation by direct UV radiation, adsorption onto photocatalysts, and oxidation by reactive oxygen species. Bacterial removal by the MPR reached a maximum at a TiO 2 dose of 1.0 g/L, with the TiO 2 dose ranging between 0 and 5 g/L. The optimal TiO 2 dose for bacterial removal appeared to be the result of the trade-off between accelerated catalytic reactions and the light obstruction by surplus catalysts. Continuous aeration required for membrane fouling control had a negative impact on bacterial removal. Although intermittent backpulsing reduced bacterial removal, its impact was not as significant as that of continuous aeration. Backpulsing frequencies and durations did not play a significant role, but the dynamic cake layer formed on the membrane was responsible for the bactericidal behavior. An increase in membrane flux deteriorated the bacterial removal performance because it resulted in shorter reaction times, even though the formation of a thicker cake layer was possible at higher fluxes. The MPR can guarantee >2.5 log removal in total bacterial count, given that the right conditions are maintained. This is significantly larger than the removal achieved by microfiltration alone (ca. 0.5 log removal).