Integrated Electric Field with Persulfate in Cathodic Ultrafiltration Membrane Process: Comparison between Peroxydisulfate and Peroxymonosulfate

In this study, with the aim of improving filtration performance, a carbon nanotube cross-linked polypyrrole ultrafiltration membrane was used as the cathode and an electro-activated persulfate methodology was employed. The performance of micropollutant removal and membrane fouling control was systemically investigated. Moreover, peroxymonosulfate (PMS) and peroxydisulfate (PDS), as oxidants, were further compared in the electro-activated membrane filtration process as E-PMS and EPDS, respectively. Both the E-PMS and E-PDS processes could effectively remove the micropollutants (such as carbamazepine, diclofenac, and sulfamethoxazole) and mitigate the membrane fouling under negative current (2.3 mA cm(-2)), while the E-PMS system had better micropollutant removal and antifouling performance than the E-PDS system. Meanwhile, the flux recovery ratio of the fouled membrane could be effectively restored through the E-PDS and E-PMS cleaning (89% and 99%). Based on the fouled membrane, the mechanism was further explored. The steady-state concentrations of generated hydroxyl and sulfate radicals in the EPMS system (3.01 +/- 0.15 x 10(-14)M and 5.43 +/- 0.21 x 10(-14)M) were significantly higher than those of the E-PDS system (0.015 +/- 0.003 x 10(-14) M and 0.045 +/- 0.004 x 10(-14 )M). In the E-PDS system, the foulant oxidation included free radical and nonradical pathways, which was only efficient against electron-rich foulants. Unlike the E-PDS system, the free radical pathway played a dominant role in the E-PMS process, which could efficiently remove both electron-rich and electron-poor foulants. Further study revealed that the removal of irreversible fouling was due to oxidative attack and electrostatic repulsion, which worked together to cause the foulants to shed off in the E-PMS/PDS filtration system. These results confirm the E-PMS process is more appropriate than the E-PDS process in improving membrane filtration performance targeting a variety of foulants. Our study will offer the possibility of utilizing E-PMS for improving filtration performance in UF application.