Advanced Tertiary Wastewater Treatment for Enhanced Effluent Quality by Electrically Conducting Membranes Operated at Altered Potential for Simultaneous Mitigation of Scaling and Biofouling

Abstract

Electrically conducting membranes (ECMs) present a promising low-fouling technology for advanced tertiary wastewater treatment, particularly when employed as cathodes to resist biofouling. However, the elevated pH levels near the cathode lead to severe scaling. This study investigated alternating the applied potentials in carbon-nanotube-based ECM to simultaneously mitigate biofouling and scaling while producing high-quality effluent. The research demonstrates that alternating −2.5 V cathodic and 1.5 V (vs Ag/AgCl) anodic potentials at 5 s intervals significantly reduce scaling and biofouling. In a 48 h filtration experiment using real secondary effluents, there was a notable decrease in trans-membrane pressure by 110 mbar, contrasting with the 320 mbar increase observed under open-circuit potential (OCP) conditions. Surface analysis confirms the absence of scaling and biofilm on the ECM layer under alternating potential operation, in contrast to high biofilm formation on the ECM at OCP conditions. The low scaling was attributed to controlled pH levels and the limited biofilm formation to the measured reactive oxygen species, facilitating bacterial detachment. The short duration of low anodic potential under alternating potential may also decrease carbon nanotube (CNT) oxidation and extend ECM lifetime. ECM-based filtration produced higher-quality effluents than conventional chlorination-coagulation-sand-filtration tertiary treatments. These findings highlight the potential of ECM-based filtration for sustained and efficient advanced wastewater treatment, surpassing the current conventional tertiary treatment technologies.