UV photoelectrochemical process for the synergistic degradation of total ammonia nitrogen (TAN)

Abstract

Abstract With increasing environmental concerns, total ammonia nitrogen (TAN) removal from water ecosystems has gained much attention. Photoelectrochemical process is considered to be an environmental-friendly technology for water purification. Meanwhile, ultraviolet light-emitting diodes (UV-LEDs) and microplasma UV radiating technologies, as promising alternatives to mercury lamp, create new pathways for the development of UV-based photoelectrochemical process. In this study, the degradation of TAN from chloride-containing solutions by direct photolysis, an electrochemical process, and particularly a photoelectrochemical process were investigated to explicate the benefits of UV radiation. A synergistic effect on TAN degradation was observed in the photoelectrochemical process with the three different UV sources. The photoelectrochemical process resulted in the acceleration of TAN removal, reduction of nitrate formation, and enhancement of current efficiencies which occurred due to the generation of active chlorine radicals by UV radiation. The effects of operating conditions (chloride concentration, initial pH, and UV irradiances) were further explored. The TAN degradation rates improved by 4.9%, 16.5%, and 18.2% in the photoelectrochemical process at corresponding chloride concentrations compared with those of the electrochemical process. The TAN degradation rates were clearly enhanced by UV radiation regardless of the initial pH values. The better synergistic degradation of TAN tended to occur under acidic conditions. The TAN degradation rate was 0.319 mg L−1 min−1 in the electrochemical process and increased to 0.366 and 0.382 mg L−1 min−1 at the irradiances of 3.06 and 6.11 mW cm−2 in the photoelectrochemical process, respectively. Although the outputs of UV-LEDs and microplasma UV lamp were comparably low, there was still a synergistic effect on the degradation of TAN. However, the pH followed a distinct tendency compared with that of the photoelectrochemical process using mercury lamp. The results demonstrate the photoelectrochemical process based on emerging UV sources could be a feasible technology for the treatment of ammonia-containing wastewaters.