Electrodialysis for the tertiary treatment of municipal wastewater: Efficiency of ion removal and ageing of ion exchange membranes

Electrodialysis was applied as a tertiary treatment for effluents from a Brazilian sewage treatment plant, and the results are discussed in terms of membrane ageing and process efficiency. Current-voltage analysis and electrodialysis (ED) treatment were performed in a bench cell. The treatment was discontinuously carried out for 930 h within one year. During the experiments, samples were collected for evaluation, and the pH, conductivity and ion concentration were monitored. Thermogravimetric analyses of the membrane were also performed. A reduction in electrical conductivity and the high ion percentage extraction demonstrated the efficiency of the ED treatment, confirming the possibility of using ED as a tertiary treatment for sewage. ED showed 100% effectiveness in terms of meeting the quality standards established by Brazilian legislation on the discharge of effluents. Additionally, important corrosive (Cl−) and encrusting ions (Ca2+ and Mg2+) that limit certain industrial uses of water were satisfactorily removed, giving the treated effluent a suitable quality for industrial purposes. The treatment did not suffer harmful fouling effects in terms of ion extraction in the membrane ageing study, indicating the possibility of long-term treatment without requiring cleaning for the membranes; however, this needs to be validated by scaling up the process.