Recovering ammonia from municipal wastewater by flow-electrode capacitive deionization

This work investigated ammonia pre-concentration from low-strength municipal wastewater by flow-electrode capacitive deionization (FCDI) cell. A variety of operating conditions, including applied voltage, flow rate, graphite powder dosage, pH value and initial ammonia concentration, were investigated systematically. The results indicated that removal efficiency was greatly improved by increasing the working voltage (from 0.2 V to 1.2 V) and flow rate (from 5.00 to 7.75 mL/min), adding 1.5 wt% graphite powders and decreasing pH to 4. The maximum ammonia removal efficiency (87.00 ± 0.79%) was obtained with adsorption capacity of 1.43 ± 0.01 mg NH4Cl/g. Based on these optimum operation conditions, enrichment experiments were conducted with the desired concentration multiple times of 20 and an initial ammonia concentration of 20 mg N/L, which led to a final ammonia concentration of 322.06 mg N/L in the aqueous phase of flow electrodes. Additionally, valence, initial concentration, hydrate radius and diffusion efficiency also notably affected the alternative electro-performance of the FCDI cell because of co-existing cations. The study provides new insights into the emerging FCDI technology, which is expected to improve the methods of performing cost-effective ammonia removal and pre-concentration from low-strength municipal wastewater with moderate ion selectivity and wide ranging influent quality.