Based on a synergistic digestion method of ultraviolet combined with ozone (UV/O3), this article investigates the reaction characteristics of nitrogen-containing compounds (N-compounds) in water and the influence of ions on digestion efficiency. In this respect, a novel and efficient AOPs-based dual-environmental digestion method for the determination of total dissolved nitrogen (TDN) in waters with complex components is proposed, in the hopes of improving the detection efficiency and accuracy of total nitrogen via online monitoring. The results show that inorganic and organic N-compounds have higher conversion rates in alkaline and acidic conditions, respectively. Meanwhile, the experimental results on the influence of Cl−, CO32−, and HCO3− on the digestion process indicate that Cl− can convert to radical reactive halogen species (RHS) in order to promote digestion efficiency, but CO32− and HCO3− cause a cyclic reaction consuming numerous •OH, weakening the digestion efficiency. Ultimately, to verify the effectiveness of this novel digestion method, total dissolved nitrogen samples containing ammonium chloride, urea, and glycine in different proportions were digested under the optimal conditions: flow rate, 0.6 L/min; reaction temperature, 40 °C; pH in acidic conditions, 2; digestion time in acidic condition, 10 min; pH in alkaline conditions, 11; digestion time in alkaline conditions, 10 min. The conversion rate (CR) of samples varied from 93.23% to 98.64%; the mean CR was greater than 95.30%. This novel and efficient digestion method represents a potential alternative for the digestion of N-compounds in the routine analysis or online monitoring of water quality.

In this study, the reaction mechanisms and kinetic of UV/O 3 digestion processes were explored with ammonium chloride and urea as the target pollutants, focused on the ozone direct oxidation and hydroxyl radical oxidation parts.Under the conditions of dual environmental digestion method, two kinds of kinetic models were proposed by competitive kinetic method with R ct based on the different scale of rate constants of hydroxyl radical oxidation. Subsequently, the second-order rate constants of ammonia (pH 11) and urea (pH 2) was determined to be 4.613 ± 0.094 and 0.378 ± 0.006 M -1 s -1 by ozone direct oxidation, and (6.154 ± 0.971) × 10 7 and (2.257 ± 0.513) × 10 6 M -1 s -1 by hydroxyl radical oxidation, respectively. Compared with contribution level of two parts to the digestion process, it was shown that in the digestion of ammonia, ozone and •OH radical contribute equally (58.86%, 41.14%). In contrast, in the case of urea, ozone (86.10%) contributes more than •OH radical.