Bipolar membrane electrodialysis for the recycling of ammonium chloride wastewater: Membrane selection and process optimization

Here, bipolar membrane electrodialysis (BMED) with BP-A configuration is employed to convert ammonium chloride wastewater into hydrochloric acid and ammonium hydroxide to overcome the shortcomings of conventional treatment methods First, different commercial anion exchange membranes (TWEDA2, AMV, JAM-II and CJMA-2) and bipolar membranes (BP-1, BPM-I and FBM) were used to conduct the BMED process. Results show that AMV and BPM-I are regarded as the optimum membranes in consideration of process performance, energy consumption and process cost comprehensively. Second, BMED process is optimized by changing current density, initial NH4Cl concentration and initial volume ratio of acid solution and NH4Cl solution. Results indicate that as current density increases from 70 to 90 mA/cm2, energy consumption and generated HCl concentration can increase from 1.51 to 2.83 kW h/kg HCl and 2.45 to 2.84 mol/L respectively, and the total process cost of 70 mA/cm2 is the highest (0.80 $/kg HCl); meanwhile, increasing initial NH4Cl concentration can increase energy consumption, generated acid concentration and total process cost; in addition, with the increment of initial volume ratio from 0.5 to 1.0, energy consumption varies between 1.46 and 1.62 kW h/kg HCl and generated acid concentration improves from 1.95 to 2.71 mol/L, while total process cost decreases from 0.63 to 0.42 $/kg HCl. In short, based on these results, the optimum operation condition is that current density is 80 mA/cm2, initial NH4Cl concentration is 1 mol/L and initial volume ratio of acid solution and NH4Cl solution is 0.67-0.83.