title: pH dependence of persulfate activation by EDTA/Fe(III) for degradation of trichloroethylene.
abstract: The ability of free ferrous ion activated persulfate (S(2)O(8)(2-)) to generate sulfate radicals (SO(4)(-)) for the oxidation of trichloroethylene (TCE) is limited by the scavenging of SO(4)(-) with excess Fe(2+) and a quick conversion of Fe(2+) to Fe(3+). This study investigated the applicability of ethylene-diamine-tetra-acetic acid (EDTA) chelated Fe(3+) in activating persulfate for the destruction of TCE in aqueous phase under pH 3, 7 and 10. Fe(3+) and EDTA alone did not appreciably degrade persulfate. The presence of TCE in the EDTA/Fe(3+) activated persulfate system can induce faster persulfate and EDTA degradation due to iron recycling to activate persulfate under a higher pH condition. Increasing the pH leads to increases in pseudo-first-order-rate constants for TCE, S(2)O(8)(2-) and EDTA degradations, and Cl generation. Accordingly, the experiments at pH 10 with different EDTA/Fe(3+) molar ratios indicated that a 1/1 ratio resulted in a remarkably higher degradation rate at the early stage of reaction as compared to results by other ratios. Higher persulfate dosage under the EDTA/Fe(3+) molar ratio of 1/1 resulted in greater TCE degradation rates. However, increases in persulfate concentration may also lead to an increase in the rate of persulfate consumption.
authors.affiliation: Department of Environmental Engineering, National Chung Hsing University, 250 Kuo-kuang Road, Taichung 402, Taiwan. cliang@dragon.nchu.edu.tw
authors.forename: Chenju
authors.initials: C
authors.lastname: Liang
authors.forename: Ching-Ping
authors.initials: CP
authors.lastname: Liang
authors.forename: Chi-Chin
authors.initials: CC
authors.lastname: Chen
mesh_terms: D004492:Edetic Acid / Q000737:chemistry*; D005290:Ferric Compounds / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D013431:Sulfates / Q000737:chemistry*; D014241:Trichloroethylene / Q000737:chemistry*; D014872:Water Movements; D018508:Water Purification
chemical_list: D005290:Ferric Compounds; D013431:Sulfates; D014241:Trichloroethylene; D004492:Edetic Acid