Ultraviolet/Hydrogen Peroxide Oxidative Degradation of 1,2,3-Trichlorobenzene: Influence of Water Matrix and Toxicity Assessment

Abstract

© Copyright 2019, Mary Ann Liebert, Inc., publishers 2019. This article investigates the effects of different water matrices emphasizing the influence of humic matter and alkalinity on the performance of ultraviolet/hydrogen peroxide (UV/H2O2) process for the degradation of 1,2,3-trichlorobenzene (TCB) in water. Due to the threat it poses to the aquatic environment and human health, TCB has been identified as a priority pollutant by the European Water Framework Directive. Under direct UV photolysis a very similar degree of TCB degradation (up to 48% depending on applied UV fluence) was achieved in synthetic matrices containing humic acids (HA) and hydrogencarbonate (HCO3-) and in natural waters. UV/H2O2 process significantly improves TCB degradation, where synthetic matrix containing HA and natural waters require application of higher H2O2 concentration to achieve >90% of TCB degradation. TCB degradation kinetics indicate that the highest inhibiting effect was observed for the matrix with a high HA concentration (12 mg C/L) and in groundwater rich in natural organic matter (NOM). TCB degradation occurred through 2,3,4-trichlorophenol as an oxidation intermediate leading to the formation of C2-C4 carboxylic acids as final products. A reduction in NOM aromaticity and aldehyde formation was observed in the treated natural waters. The bioassay with Vibrio fischeri shows that a slight inhibition of bioluminescence recorded for untreated samples was not significantly changed during UV photolysis or by the UV/H2O2 process with 1 mg H2O2/L (10-18% of inhibition), but applying higher H2O2 concentrations rapidly increased the inhibition indicating the formation of more toxic intermediates of TCB and NOM during oxidation.