Removal of ammonia nitrogen in wastewater by microwave radiation

Ammonia nitrogen contaminated wastewater has posed great threat on the safety of water resources. In this study, a novel process, microwave (MW) radiation, was developed for the removal of ammonia nitrogen from wastewater. The effects of pH, radiation time, aeration and initial ammonia concentration on the removal were investigated. pH and radiation time showed significant influence on the removal of ammonia nitrogen. The largest removal was obtained at pH 11 in 3 min. Initial ammonia concentration and aeration had minute influence. The mechanism of ammonia removal was proposed as the formation of molecular ammonia (NH3) and the subsequent evaporation of NH3 by MW radiation. Compared with conventional heating (CH) mode, MW radiation led to higher ammonia removal. Both thermal and non-thermal effects were responsible for the removal, but the contribution of thermal effect was more significant. In the end, coke-plant wastewater containing high concentration of ammonia nitrogen was treated by MW radiation. With the initial ammonia concentration of 5000 mg/L at pH 11, ammonia was reduced to 350 mg/L at 750 W by 10 min MW radiation. It could be proposed that MW radiation was an effective method for the removal of ammonia nitrogen from wastewater.