Ammonia removal from municipal wastewater via membrane capacitive deionization (MCDI) in pilot-scale

With the depletion of energy, renovation of wastewater has attracted wide attention around the world, among which the recovery of ammonia has also been an ongoing topic. Membrane capacitive deionization (MCDI) has emerged as a promising technology for nutrient removal and recovery. However, limitations of both scale-up and treatment of practical wastewater still restrict its real application. This study aims to investigate the feasibility of ammonia removal from real wastewater by MCDI on a pilot scale. The MCDI module used in this study was expanded to a 2-unit facility (15 pairs of electrodes per unit). Firstly, synthetic wastewater was used as feed water to optimize different kinds of operating parameters, including applied voltage (0–2.5 V), flow rate (7–30 L/h), and initial concentration (20–100 mg/L). Further experiments investigated the competitive adsorption performance under complex inflow conditions. Results indicated that the presence of co-existing cations significantly reduced the removal efficiency and adsorption capacity of ammonia. With the same inflow concentration, the removal efficiency of NH4+, Mg2+, and Ca2+ was 39.12 ± 5.31%, 47.56 ± 2.68%, and 33.33 ± 1.90% respectively. The interplay of initial ion concentration, charge valence, and hydrated radii led to the different electro-sorption performances. Subsequently, practical municipal wastewater after the up-concentration of organics was used as feed water to evaluate the feasibility of the pilot-scale MCDI. Under the optimized condition, a long-term experiment was carried out for 15-day to deal with actual wastewater. Besides, ion removal performance, the energy consumption, and desorption efficiency were also analyzed. The system maintains a stable removal efficiency for all cations, with low energy consumption (1.16 kWh/m3) and high desorption efficiency (around 90%). Overall, the results of this study posed the MCDI process as a potential approach to ammonia removal and recovery from municipal wastewater.