Nitrate enhanced the carbon tetrachloride degradation in the UV/HCOOH reductive system

Abstract

Catalytic hydrodechlorination is one of the most effective methods for remediating chlorinated organic wastewater. The influence of nitrate on the production capacity of the carbon dioxide radical anion (CO2·-) and the reduction efficiency of carbon tetrachloride (CT) in an ultraviolet/formic acid (UV/HCOOH) system was evaluated in this study. In the water distribution system, nitrate enhanced the degradation efficiency of CT (5 mg L−1) from 19.1 % to 95.2 % using formic acid (20 mM) under UV radiation, and the degradation rate was positively related to the nitrate concentration. Chloroform was the main by-product during the CT reduction and conversion and could be further dechlorinated to dichloromethane. Moreover, the environmental adaptability of UV/HCOOH/NO3 was better than that of UV/HCOOH over a wide pH range, and the degradation efficiency of CT in the UV/HCOOH/NO3 system was 83.4 % at pH 12. Except for the high concentrations of bicarbonate ions and humic acid, chloride and sulfate had little effect on the CT reduction efficiency in the UV/HCOOH/NO3 system. Experiments by electron paramagnetic resonance and quenching experiment showed that CO2·- radicals were primarily responsible for the CT reduction. In the water distribution system, the addition of nitrate enhances the rate of CO2·- radical generation in the UV/HCOOH system. The novel insights in this study highlight the significant potential of nitrate solutions to repair chlorinated solvents by enhancing the generation of CO2·- radicals in UV/HCOOH systems.