Removal of organic micropollutants from wastewater using nanofiltration and concentrate recirculation: A one-year pilot study

The presence of organic micropollutants (OMPs) in the water cycle raises concerns due to their potential environmental impact. Wastewater treatment plants form a main entry point for these compounds. Nanofiltration is a promising complementary technology for the removal of OMPs. However, long-term seasonal studies for such integrated systems are lacking. The aim of this study was to investigate the performance and stability during one full year of a 1 m³/h pilot-scale wastewater treatment process, formed by an activated sludge process followed by a hollow fibre nanofiltration membrane system, of which the concentrate was recycled back to the bioprocess. The pilot demonstrated stable performance with respect to bulk organics and nutrient removal, achieving an overall removal for COD, TN and TP of 91%, 78% and 70%, respectively. The membrane process showed a rather small decrease in membrane permeability of 15%. The impact of concentrate recirculation on OMP removal was compound-dependent. Compared to a (conventional) bioprocess only, for the integrated process a significant increase in overall removal was observed for 5 out of 12 OMPs monitored: metformin, atenolol, amisulpride, diclofenac and sotalol. Although a significant decrease in removal was observed for sulfamethoxazole, the average total OMP removal increased. Furthermore, the results showed significant differences in removal per season for several OMPs, highlighting the importance of good operation management. Further optimization of the pilot is desirable to fully assess its potential for enhancing OMP removal.