Simultaneous deammoniation and denitrification under vacuum ultraviolet irradiation.

The oxidative nitrate (NO) and reductive ammonium (NH) constitute the common nitrogen pollution in water. However, the high energy barrier of the comproportionation reaction makes it challenging for the deammoniation and denitrification reactions to occur simultaneously. This study evaluated the performance of simultaneous deammoniation and denitrification under vacuum ultraviolet (VUV) irradiation. The results demonstrate that the reduction reaction of NO and the oxidation reaction of NH conform to the pseudo-first-order reaction kinetics, with respective kinetic constants of 0.012 min and 0.002 min. The presence of Cl and SO inhibits the reduction of NO, while HCO and CO promote NO reduction and NH oxidation. The reaction mechanism of simultaneous NO and NH removal was proven through free radical capture and electron spin resonance (ESR) experiments. It was determined that NO was reduced to NO, NH, and N by hydrated electrons (e) in turn. While the free hydroxyl radical (·OH) produced by direct photolysis of water by VUV was identified as the key to the oxidation of NH. When NO and NH coexist, they can capture e and ·OH, respectively, thus avoiding the quenching of the two highly active species. Thus, energy waste is avoided and nitrogen removal efficiency is improved. The process study shows that the adjustment of the NO and NH ratio and the control of process conditions are essential for the synchronous conversion of nitrate and ammonium.