Scale-up and performance evaluation of an electrodialysis process in a municipal wastewater treatment plant

• Validation of electrodialysis process for desalinating real wastewater from WWTP with by high. • Success of electrodialysis process under complex operation in real scenario. • Validation of an electrodialysis scale-up from synthetic water in a pre-pilot system to real water in a pilot system at a WWTP. • Mitigation of Ca 2+ and Mg 2+ salt precipitation in the electrodialysis system through electrolyte optimization and operation control. Seawater intrusion in pipeline systems of coastal Spanish cities represents a major problem since current national regulations establish that the conductivity of discharge wastewater must be below 3 mS·cm -1 . The reuse for agricultural use is denied as well for the same reason. Electrodialysis (ED) is an energy-affordable membrane technology that desalinates moderate conductivity water without removing beneficial elements for plants. In this study, a pre-pilot and an in-situ pilot ED systems were successfully evaluated to test the capability of desalinate tertiary wastewater from Santa Pola’s wastewater treatment plant (WWTP). At pre-pilot scale, current efficiencies close to 90 % were achieved, and energy consumption between 0.42 and 1.34 kWh·m -3 . Scaling the process up to an in-situ pilot achieved current efficiencies above 60 % and an electric consumption between 0.15 and 0.34 kWh·m -3 , with water recovery above 80 %, treating a continuous flow rate of 600 L·h -1 . The wastewater conductivity was reduced from 4-7 mS·cm -1 (depending on the month of the year) to 2.5 mS·cm -1 . The ED pilot reactor is composed of 60 cells and an electrode area of 1000 cm 2 . It was demonstrated that appropriate wastewater pre-filtration and ultraviolet pretreatment is mandatory for the long-term viability of the ED process.