Removal of total ammoniacal nitrogen from reject water through selective electrodialysis reversal and bipolar electrodialysis

The removal of ammonium and ammonia, represented as total ammoniacal nitrogen (TAN), from reject water through electro-dialysis (ED) and bipolar membrane electrodialysis (BPMED) encounters challenges such as organic fouling, NH3 back-diffusion, and high energy consumption. The efficacy of electrodialysis reversal (EDR) combined with bipolar membrane electrodialysis using cation-exchange membranes (BPC) was assessed as a more practical configuration (EDR + BPC). Additionally, a novel configuration involving monovalent selective cation-exchange membranes (MSCEMs) in an EDR + BPC setup (SEDR + BPC) was investigated. Comparisons were made among BPMED, EDR + BPC, and SEDR + BPC under three load ratios (LN) of 0.8, 1, and 1.3 during continuous operation. The innovative SEDR + BPC configuration, with an LN of 0.8, exhibited the lowest energy consumption for transported TAN (ETAN) at 4.4 MJ·kgN−1 removal and achieved the highest TAN removal efficiency of 78 % with an LN of 1.3. In contrast to conventional BPMED, SEDR + BPC allowed for the recovery of potentially back-diffused NH3 into the acid chamber, minimizing transport losses. Furthermore, scaling in the base chamber was reduced due to the contribution of MSCEMs when applying an LN of 0.8. The MSCEMs increased the molar ratio of TAN over (Mg2+ + Ca2+) in the concentrate and decreased it in the diluate. EDR + BPC and SEDR + BPC configurations exhibited stable and lower cell resistance throughout the operation compared to BPMED, attributed to their ability to generate higher concentration gradients. The results clearly demonstrated the feasibility of low-energy TAN removal from real reject water from sludge anaerobic digestion using the SEDR + BPC setup.