Nanofiltration concentrate addition to domestic wastewater does not substantially suppress nitrifying activity and micropollutant removal in batch experiments

ABSTRACT

Conventional biological wastewater treatment plants are not generally designed for organic micropollutant removal. Nanofiltration removes these micropollutants, producing a concentrate stream which may be recirculated into biological treatment. This principle was investigated in batch experiments, testing two sources of sludges and two media combinations (wastewater with nanofiltration concentrate). Although responses of two inocula were different, under these experimental conditions, nitrification activity was not substantially inhibited by concentrate addition and even doubled when initial micropollutant concentrations reached 100 μg/L. Among the 13 micropollutants tested, nanofiltration effectively rejected bezafibrate, irbesartan and diclofenac (>96% rejection), increasing their concentrations by 30% in the batch experiments. At low concentrations (0–10 μg/L), atenolol, bezafibrate and sulfamethoxazole were removed the most (64 ± 3 to 83 ± 13%). Whereas, at higher concentrations (100 μg/L), the removal increase was +68, +64 and +41% for irbesartan, diclofenac, and venlafaxine for sludge A, and +114, +83 and +65% for sulfamethoxazole, diclofenac and irbesartan for sludge B, respectively. Amisulpride and carbamazepine were highly persistent to biodegradation, and atenolol and trimethoprim were mostly removed by sorption to biomass. These results indicate that enhanced removal of biodegradable micropollutants is possible and nanofiltration concentrates can be recirculated into the biological system without jeopardising the wastewater nutrient removal.