Degradation of 2, 4-dichlorophenol in aqueous solution by dielectric barrier discharge: Effects of plasma-working gases, degradation pathways and toxicity assessment.

Chlorinated phenols are a class of contaminants found in water and have been regarded as a great potential risk to environment and human health. It is thus urgent to develop effective techniques to remove chlorinated phenols in wastewater. For this purpose, we employed dielectric barrier discharge (DBD) in this work and studied the efficiency of DBD for the degradation of 2,4-dichlorophenol (2,4-DCP), one of the most typical chlorophenols in the environment. The effects of pH value, applied voltage and plasma-working gases on the dichlorophenol-removal efficiency were investigated. The results demonstrate that DBD plasma could successfully degrade 2,4-DCP, achieving efficiency of 98.16% (k = 1.09 min) in the Ar-DBD system, and 77.60% (k = 0.48 min) in the N-DBD system, with the process following the first-order kinetics. The removal efficiency was reduced in the presence of radical scavengers, confirming that hydroxyl radicals played a key role in the degradation process, while other active substances were also found such as nitrogen radicals in the N-DBD system, which was found to have also contribution to the degradation of 2,4-DCP. The intermediates and final products generated in the degradation process were analyzed using gas chromatography-mass spectrometry (GC-MS). Based on the identification of intermediates, the degradation pathways and mechanism were proposed and discussed. Besides, the toxicity of the DBD treated 2,4-DCP solution was also assessed using GFP-expressing recombinant Escherichia coli (E. coli) as the testing organism, showing that plasma treatment could substantially reduce the toxic effect of 2,4-DCP.