Application of an electrochemical-ion exchange reactor for ammonia removal

A new concept for ammonia removal from aqueous solution by zeolites followed by electrochemical oxidation/regeneration was studied in this work. In the first mode, (NH4)2SO4 solution is passed through an ion exchange column where ammonium is concentrated in the zeolite. During the second mode (electrochemical oxidation/regeneration), the absorbed ammonia is harmlessly removed by electrochemical oxidation in the presence of sodium chloride (NaCl) and simultaneously the zeolite is regenerated. Continuous experiments were carried out for 172 h with five loading and four regeneration cycles without finding the loss of ammonia removal capacity of the zeolite. With electrochemical oxidation/regeneration, the conversion rate of ammonia adsorbed by the zeolites into nitrogen gas was more that 98%, and the conversion rate to nitrate was less than 2%; no ammonia or nitrite was detected in the regenerated solution. The regeneration solution can be repeatedly reused over a long period of time with 2.0 g/L NaCl added to the regeneration solution, saving both water resources and the chemical reagent. Moreover, approximately five times less energy was consumed with the present method than that of the direct electrochemical oxidation of ammonia.