Electrodialysis in zero liquid discharge systems for sustainable brine management

According to the latest environmental requirements, zero liquid discharge principle must be considered in all modern manufacturing processes. In principle, solid waste can be achieved only by evaporation plus crystallization, and therefore reverse osmosis is usually applied to decrease the operation expenses by pre-concentrating the evaporator feed. However, reverse osmosis can generally only achieve concentrates of about 80 g/kg, still leaving a significant gap before saturation of common salts is reached. Electrodialysis can double this concentration, cutting the evaporator operating expenses or even eliminating the evaporator at all, providing the concentrate can be directly fed to crystallization. In this work an array of the most common brines was tested on a lab-scale electrodialysis unit, and salt transport, electricity consumption and electric current efficiency was evaluated. More attention was given to optimization of operating conditions, and the effect of polarity reversal and chemical cleaning was evaluated. No performance drop in either scale-up factor was observed at the maximum concentrations, suggesting that under right operating conditions, integrated membrane processes should significantly decrease the evaporator costs and provide economic feasibility of zero liquid discharge process in waste brine treatment.