Electrochemically assisted water softening with disinfectant production for wastewater reuse

Highly purified wastewater has great potential for potable reuse but its treatment by commonly used technologies like reverse osmosis (RO) is facing challenges of membrane scaling/fouling. Herein, a chemical-free electrochemically assisted treatment process was developed and investigated for water softening with simultaneous disinfectant production; such a process could serve as a pretreatment step to control scaling/fouling in the subsequent RO treatment. The secondary effluent sampled from a local wastewater treatment plant was firstly treated by OH⁻-containing catholyte to raise the solution pH to ∼11 for hardness removal, and subsequently treated by H⁺- and chlor(am)ine-containing anolyte to adjust pH and achieve disinfection. The electrochemical treatment has decreased Ca²⁺ and Mg²⁺ from 1.8 and 0.9 mM to 0.3 and 0.4 mM with removal efficiencies of >80 % and > 50 %, respectively. Meanwhile, total coliform and E. coli were reduced by >5-log and > 4-log, and the final effluent had a pH of ∼7 and a residual chloramine concentration of ∼0.04 mM that would be suitable for further control of microbial contaminants. After 50-cycle operation, cathodic scaling was observed to reduce the cathodic OH⁻ generation from 9.10 to 6.03 mM, resulting in an increase in energy consumption from 3.1 to 4.5 kWh m⁻³. A mild acidic washing method was employed to remove scale deposits and recover cathodic OH⁻ generation performance, enabling additional 30 cycles of consistent performance. Those results would encourage further exploration of electrochemical processes as a chemical-free pretreatment method for RO membrane fouling control in potable reuse.