Micropollutants removal and operating strategies in ultrafiltration membrane systems for municipal wastewater treatment: Preliminary results

Membrane systems are reported to enhance the removal of micropollutants (heavy metals and organic persistent compounds) from wastewaters. However, with regard to real municipal wastewater, where the micropollutants are present at very low concentrations, the debate on the real convenience of operating membrane systems is still ongoing. This paper presents the preliminary results from a pilot study where the removal of several micropollutants (80 compounds, grouped in the families of metals and metalloids, polynuclear aromatic hydrocarbons (PAH), volatile organic compounds (VOC), halogenated volatile organic compounds (HVOC)) from real municipal wastewater was studied using an ultrafiltration membrane system. With the purpose to optimize the removal performances, the prime objective was to determine the best plant configuration, tertiary filtration, or membrane bioreactor, as well as the best operating parameters, with particular concern to the activated sludge concentration. To expand the practical interest of the results for application in real plants, the sludge filterability also was studied according to different activated sludge concentrations and permeate fluxes. The objective was to estimate operating parameters able to enhance the removal of micropollutants and optimize the ultrafiltration process. After one year of experimentation, the results that were obtained gave important indications about the real role of the membrane system. The membrane not only demonstrated that it could be a simple barrier against the particulate pollutants, but it also demonstrated that it can enhance the removal of dissolved micropollutants, thanks to the "layer effect".