title: In-situ activation of persulfate by iron filings and degradation of 1,4-dioxane.
abstract: Activation of persulfate by iron filings and subsequent degradation of 1,4-dioxane (dioxane) was studied in both batch-reactor and column systems to evaluate the potential of a persulfate-enhanced permeable reactive barrier (PRB) system for combined oxidative-reductive removal of organic contaminants from groundwater. In batch experiments, decomposition of persulfate to sulfate and degradation of dioxane both occurred rapidly in the presence of iron filings. Conversely, dioxane degradation by persulfate was considerably slower in the absence of iron filings. For the column experiments, decomposition and retardation of persulfate was observed for transport in the columns packed with iron filings, whereas no decomposition or retardation was observed for transport in columns packed with a reference quartz sand. Both sulfate production and dioxane degradation were observed for the iron-filings columns, but not for the sand column. The pH of the column effluent increased temporarily before persulfate breakthrough, and significant increases in both ferrous and ferric iron coincided with persulfate breakthrough. Multiple species of free radicals were produced from persulfate activation as determined by electron paramagnetic resonance (EPR) spectroscopy. The impact of the oxidation process on solution composition and iron-filings surface chemistry was examined using ICP-MS, SEM-EDS, and XRD analyses. A two-stage reaction mechanism is proposed to describe the oxidation process, consisting of a first stage of rapid, solution-based, radical-driven decomposition of dioxane and a second stage governed by rate-limited surface reaction. The results of this study show successful persulfate activation using iron filings, and the potential to apply an enhanced PRB method for improving in-situ removal of organic contaminants from groundwater.
authors.affiliation: Soil, Water, and Environmental Science Department, School of Earth and Environmental Sciences, University of Arizona, Tucson, AZ 85721, USA. Electronic address: zhonghua@email.arizona.edu.
authors.forename: Hua
authors.initials: H
authors.lastname: Zhong
authors.affiliation: Soil, Water, and Environmental Science Department, School of Earth and Environmental Sciences, University of Arizona, Tucson, AZ 85721, USA; Hydrology and Water Resources Department, School of Earth and Environmental Sciences, University of Arizona, Tucson, AZ 85721, USA. Electronic address: Brusseau@email.arizona.edu.
authors.forename: Mark L
authors.initials: ML
authors.lastname: Brusseau
authors.affiliation: Soil, Water, and Environmental Science Department, School of Earth and Environmental Sciences, University of Arizona, Tucson, AZ 85721, USA. Electronic address: yakew@email.arizona.edu.
authors.forename: Yake
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Hydrology and Water Resources Department, School of Earth and Environmental Sciences, University of Arizona, Tucson, AZ 85721, USA. Electronic address: niyan@email.arizona.edu.
authors.forename: Ni
authors.initials: N
authors.lastname: Yan
authors.affiliation: Civil & Environmental Engineering, Maseeh College of Engineering & Computer Science, Portland State University, Portland, OR 97201, USA. Electronic address: lquig@pdx.edu.
authors.forename: Lauren
authors.initials: L
authors.lastname: Quig
authors.affiliation: Civil & Environmental Engineering, Maseeh College of Engineering & Computer Science, Portland State University, Portland, OR 97201, USA. Electronic address: gjohnson@pdx.edu.
authors.forename: Gwynn R
authors.initials: GR
authors.lastname: Johnson
mesh_terms: D004146:Dioxanes / Q000737:chemistry*; D060587:Groundwater / Q000032:analysis*; D007501:Iron / Q000737:chemistry*; D013058:Mass Spectrometry; D008855:Microscopy, Electron, Scanning; D010084:Oxidation-Reduction; D013052:Spectrometry, X-Ray Emission; D013431:Sulfates / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000737:chemistry*; D018508:Water Purification / Q000379:methods*; D014961:X-Ray Diffraction
chemical_list: D004146:Dioxanes; D013431:Sulfates; D014874:Water Pollutants, Chemical; D007501:Iron; C025223:1,4-dioxane
keywords: Dioxane; Iron filings; Permeable reactive barrier; Persulfate; Radical; Surface reaction