Study On P-chlorophenol Degradation By Pulsed High Voltage Discharge Coupling Internal Electrolysis

Certain cast iron scrap(CIS) was introduced into pulsed high voltage discharge system to form a synergistic system of pulsed high voltage discharge coupling internal electrolysis (PHVDCIE). The process of 4-chlorophenol (4-CP) degradation by the PHVDCIE system were investigated in the paper. The formation rates of chemically active species such as·OH and H₂O₂ in the PHVDCIE system were determined, and the mechanism of the promoting effects and the intermediate products during 4-CP degradation in the coupling process was discussed. The main results presented in the paper are as follows:(a) The best removal efficiency of 4-CP was achieved when 15 g CIS was added to the pulsed high voltage discharge system, and the removal percent was improved from 70% to 90% as compared with no CIS addition.(b) In the PHVDCIE system, the 4-CP removal rate was highest by using the ground electrode of 20 mesh stainless steel wire amoug the 10, 20 and 30 mesh stainless steel wire electrodes.(c) In the PHVDCIE system, higher removal rates of 90% could be reached for about 36 min treatment at various original pH.(d) The 4-CP removal rate was highest when bubbling oxygen and much higher than others in two different discharge systems. Under the same gas bubbling condition, the 4-CP removal rate in the coupling system was always higher than that in the sole pulsed discharge system.(e) There was much residual hydrogen peroxide which was not utilized during 4-CP degradation by sole pulsed discharge. But in the PHVDCIE system, most of the hydrogen peroxide could be used. Ferrous ions generated by internal electrolysis reactions could induce the residual hydrogen peroxide to regenerate a large amount of hydroxyl radical by Fenton's reaction in PHVDCIE system. More hydroxyl radicals could be utilized for 4-CP degradation, which accounts for the enhancing effect of 4-CP degradation in the PHVDCIE system.(f) The main path for 4-CP degradation was that·OH radical attacked on the ortho position of the hydroxyl or the Cl-position to form 4-chlorocatechol, catechol and hydroquinone. Hydroquinone was oxidized to form p-benzoquinone. Then these phenyl compounds could be oxidized to open the ring and formed formic acid, acetic acid, oxalic acid and chloride ions.