Removal of 2,4-dichlorophenol and triclosan by fenton and electro-fenton processes

Abstract

2,4-Dichlorophenol (2,4-DCP) and triclosan are defined as endocrine disruption organic compounds and toxic pollutants as listed by the U.S. EPA. The advanced oxidation processes in the type of Fenton and electro-Fenton processes were investigated in order to ascertain the process optimization, kinetics of process and the feasibility of intermediate occurring during the process for enhancement of 2,4-DCP and triclosan degradation. The effect of operating parameters such as pH, current density, Fe²⁺ and H2O2 concentration, H₂O₂ to Fe²⁺ (H/F) molar ratio and H₂O₂ feeding mode of operation were investigated to determine the evolution of 2,4-DCP and triclosan which were used to indicate the optimum operating conditions. Additionally, the initial degradation rate was also used as a process optimization indicator. 2,4-DCP and triclosan can be oxidized up to 70-100% under various conditions depends on the effect of operating parameters. The performance of the process when using the H₂O₂ step feed condition was found to be better than that of the conventional initial feed as shown by a better mineralization. The novel kinetic model of the electro-Fenton process was proposed to be employed with 2,4-DCP and triclosan as a chlorinated organic reference to determine the kinetic rate constant of process. The operating parameters; pH, current densities and H₂O₂ concentrations were varied to validate this novel model and intrinsic kinetic rate constant determination. The kinetic rate constant of •OH with 2,4-DCP and triclosan obtained by the novel model from this experiment was 1.437 x 109 M-1s-1 for 2,4-DCP and 5.434 x 109 M-1s-1 for triclosan. As a result, the correlation coefficients demonstrated that the novel model can well describe the kinetics of chlorinated organic compound degradation more suitably and better than pseudo 1st-order model. In the electro-Fenton process, 2-chlorophenol, phenol, hydroquinone, p-benzoquinone, maleic, acetic, oxalic and formic acids were the main oxidation intermediates of 2,4-DCP degradation whereas 2,4-DCP, 4-chlorocatechol, phenol, hydroquinone, p-benzoquinone, maleic, acetic, oxalic and formic acids were the main oxidation intermediates of triclosan degradation. The occurrence of intermediates depended on the H₂O₂ feeding mode of process majority. The degradation pathway for 2,4-DCP and triclosan degradation by electro-Fenton process were proposed on the basis of the intermediate compounds that were detected.