Evaluation of enhanced coagulation combined with densadeg-ultrafiltration process in treating secondary effluent: Organic micro-pollutants removal, genotoxicity reduction, and membrane fouling alleviation.

Conventional coagulation is widely used as an ultrafiltration membrane pretreatment process in wastewater reclamation, however it shows little ability to reduce organic micro-pollutants (OMPs) and genotoxicity. In this research, powdered activated carbon (PAC) and potassium ferrate were used respectively with polyaluminum chloride (PACl) to enhance coagulation. Filtration experiments of coagulation (CUF), coagulation-adsorption (CAUF) and coagulation-oxidation (COUF) pretreatment combined with densadeg-ultrafiltration processes were conducted under their optimum doses. The effluent water quality of CAUF and COUF could meet the water reuse quality standard for scenic environment use, while total phosphorus in the conventional CUF discharge was higher than the standard. The average removal efficiency of the selected fourteen OMPs was significantly improved by 1.8 times through the CAUF process compared to the CUF process (31.2%), whereas the COUF process (38.4%) showed limited improvement. Prominent reduction of genotoxicity was observed in the CAUF and COUF processes, and the effluent of the CAUF process had the least genotoxicity of 1.0 ± 0.3 μg 4-Nitroquinoline-N-oxide (4-NQO)/L. Moreover, the average transmembrane pressure increasing rate followed the order of CUF (1.5 kPa/d) > COUF (1.1 kPa/d) > CAUF (0.6 kPa/d), indicated that the enhanced coagulation process could relieve membrane fouling effectively.