Navigating the balance between nanofiltration and oxidation to remove organic micropollutants from wastewater treatment plant effluent

The removal of organic micropollutants (OMPs) from wastewater treatment plant effluent is becoming more important due to the adverse effects of these compounds on the environment. To overcome the limitations of currently available technologies, this study proposes a combination of hollow fiber membrane filtration with advanced oxidation to remove OMPs. The possible synergy between these processes was investigated. The nanofiltration membrane ensures the removal of organic matter and thus an improvement of transmittance, after which oxidation with UV/H2O2 of the permeate can remove OMPs more effectively and at a significantly lower energy consumption than without a membrane. Six membranes were evaluated with a pure water permeability between 6.7 and 106 Lm−2 h−1 bar−1 and a MgSO4 retention ranging from 0.93 to 0. The molecular weight cut-off (MWCO) varied from 250 Da to more than 10 kDa. The measured MWCO can depend strongly on the applied flux. The UV-transmittance of NF permeate of treated wastewater was investigated experimentally to be between 97 and 50%. These values were used for an estimation of the specific energy consumption (SEC) for the membrane and the oxidation step, resulting in a combined SEC of 0.17-0.18 kWhm−3 for 70 or 80% removal of OMPs, respectively. Remarkably, this lowest SEC was not found for the combination with the most dense membrane, but for a slightly more open membrane. The reported SEC is comparable to the total energy consumption required for ozonation and adsorption, while producing clean water with a double barrier, high transmittance and 70-80% removal of OMPs.