Mechanism for the destruction of carbon tetrachloride and chloroform DNAPLs by modified Fenton's reagent
Introduction
The presence of dense non-aqueous phase liquids (DNAPLs) at contaminated sites represents significant environmental and public health problems. Approximately 60% of the sites on the National Priorities List (NPL) are contaminated with DNAPLs in the form of large pools, smear zones, or ganglia (U.S. EPA, 1993). Dissolution of DNAPLs into ground water is slow, providing a continuous source of contamination emanating from contaminated sites. Dissolution is usually the rate-limiting step in DNAPL remediation; therefore, DNAPLs may persist for decades, even when actively treated (Johnson and Pankow, 1992, Lemke et al., 2004).
Numerous approaches have been proposed for the in situ treatment of DNAPLs. Traditional technologies, such as bioremediation and pump and treat systems, are limited by dissolution and mass transfer rates and may require decades for complete DNAPL destruction (Stroo, 2003). Other technologies include thermal treatment (Hawthorne et al., 2000, Kuhlman, 2002, Kaslusky and Udell, 2002) and DNAPL mobilization methods, such as the addition of surfactants (Pennell et al., 1993), solvents (Kibbey et al., 2002), and dense brine water (Miller et al., 2000, Hill et al., 2001). Each of these processes has limitations: thermal treatment is expensive, and mobilization methods move the DNAPL but do not destroy it.
In situ chemical oxidation (ISCO) technologies have recently gained increased popularity for soil and ground water treatment, with 33% of recent cleanup efforts employing ISCO technologies (Hood, 2004). Trichloroethylene (TCE) and perchloroethylene (PCE) DNAPL destruction has been demonstrated using permanganate ISCO (Vella and Veronda, 1992, Schnarr et al., 1998, Nelson et al., 2001). Permanganate destruction of DNAPLs has been improved by the use of phase-transfer catalysts to enhance the penetration of permanganate into DNAPLs (Seol and Schwartz, 2000); however, this technology has also led to decreased subsurface permeability and clogging (Schroth et al., 2001).
Modified Fenton's reagent was one of the first ISCO processes studied (Watts et al., 1990), and it has recently been investigated for DNAPL destruction (Yeh et al., 2003, Watts et al., 2005). Modified Fenton's reagent is based on the standard Fenton reaction in which the decomposition of dilute hydrogen peroxide is initiated by iron (II), resulting in the generation of hydroxyl radical (OH•):Fe2+ + H2O2 → Fe3+ + OH• + OH−.
Hydroxyl radical is a powerful, relatively non-selective oxidant capable of degrading most contaminants of concern (Dorfman and Adams, 1973, Buxton et al., 1988, Haag and Yao, 1992). The reaction is usually modified for ISCO by the use of alternative initiators, such as iron (III) (Watts and Dilly, 1996), iron chelates (Sun and Pignatello, 1992) and iron minerals (Tyre et al., 1991, Watts et al., 1993, Ravikumar and Gurol, 1994, Miller and Valentine, 1995, Kwan and Voelker, 2003). Another modification is the addition of excess hydrogen peroxide, which promotes a series of propagation reactions (Walling, 1975, De Laat and Gallard, 1999) that result in the formation of the reactive species perhydroxyl radical (HO2•), superoxide radical anion (O2•−) and hydroperoxide anion (HO2−):OH• + H2O2 → HO2• + H2OFe3+ + H2O2 → Fe2+ + HO2• + H+HO2• → O2•− + H+ (pKa = 4.8)HO2• + Fe2+ → Fe3+ + HO2−
Hydroperoxide, the conjugate base of hydrogen peroxide (pKa = 11.75), is a strong nucleophile (Edwards and Pearson, 1962, David and Seiber, 1999). Perhydroxyl radical is a weak oxidant that has minimal reactivity in aqueous systems (Afanas'ev, 1989). Superoxide is a nucleophile and a reductant and has been identified as the reactive species in modified Fenton's reagent responsible for the degradation of carbon tetrachloride dissolved in water (Smith et al., 2004).
Although hydroxyl radical-mediated oxidations have been the degradation mechanism most commonly associated with Fenton's reagent, hydroxyl radical reacts at diffusion-controlled rates and is not reactive with sorbed compounds (Sedlak and Andren, 1994, Watts et al., 1999), so it is not likely to react with non-aqueous phase contaminants (Sheldon and Kochi, 1981). However, rapid destruction of such DNAPLs has been demonstrated with modified Fenton's reagent in the laboratory for a TCE DNAPL (Yeh et al., 2003) and a carbon tetrachloride DNAPL (Watts et al., 2005). Such rapid destruction has also been observed in the field; for example, 94% of a 270-kg TCE DNAPL was destroyed at the Westinghouse Savannah River site using modified Fenton's reagent (U.S. EPA, 1998). Reactive oxygen species other than hydroxyl radical generated through propagation reactions are important in Fenton's ISCO (Watts et al., 1999, Watts and Teel, 2005) and may be responsible for the rapid treatment of DNAPLs. However, the destruction of DNAPLs by modified Fenton's reagent is complex and is affected not only by the rates of reaction of the contaminant with hydroxyl radical, superoxide, and other reactive oxygen species, but also by the rate of dissolution of the contaminant, the surface to volume ratio of the DNAPL, and many other possible factors (Stroo et al., 2003). The objective of this research was to determine the rates of DNAPL destruction in relation to the rates of DNAPL dissolution for chloroform and carbon tetrachloride, and to determine the reactive oxygen species responsible for the destruction of these DNAPLs.
Section snippets
Materials
Iron (III) sulfate [Fe2(SO4)3], magnesium hydroxide (> 99%), and sodium hydroxide (> 99%) were obtained from VWR (West Chester, PA). Carbon tetrachloride (99.9%), chloroform (trichloromethane) (99.9%), potassium superoxide (KO2), diethylenetriamine-pentaacetic acid (DTPA), decane (> 99%), and hexaketocyclohexane (HKCH) (97%) were purchased from Sigma-Aldrich (St. Louis, MO). Toluene (> 99%), ethanol (> 99%), and propanone (acetone) (99.6%) were purchased from Fisher Scientific (Hampton, NH). ORBO®
Carbon tetrachloride and chloroform DNAPL destruction by modified Fenton's reagent
The destruction of a carbon tetrachloride DNAPL and a chloroform DNAPL by modified Fenton's reagent is shown in Fig. 2A–B. The total mass lost from the carbon tetrachloride DNAPL was 84% and from the chloroform DNAPL was 62% over 24 h. After subtracting the masses of carbon tetrachloride and chloroform captured in the ORBO tubes and dissolved into the aqueous phase, the net destruction of the carbon tetrachloride DNAPL was 74% and the net destruction of the chloroform DNAPL was 44%. In parallel
Summary and conclusions
The destruction of carbon tetrachloride and chloroform DNAPLs by modified Fenton's reagent was investigated, and the reactive oxygen species responsible for their destruction was evaluated using systems that generate only (1) hydroxyl radical, (2) hydroperoxide, and (3) superoxide. A carbon tetrachloride DNAPL was effectively destroyed by modified Fenton's reagent at a rate 6.5 times that of gas purge dissolution. The carbon tetrachloride DNAPL was not destroyed by hydroxyl radical or
References (56)
- et al.
Scatchard analysis of methane sulfinic acid production from dimethyl sulfoxide: a method to quantify hydroxyl radical formation in physiologic systems
Free Radic. Biol. Med.
(1989) - et al.
Preparation and stabilization of aqueous/ethanolic superoxide solutions
Anal. Biochem.
(1983) - et al.
Accelerated hydrolysis of industrial organophosphates in water and soil using sodium perborate
Environ. Pollut.
(1999) - et al.
A theoretical model of air and steam co-injection to prevent the downward migration of DNAPLs during steam-enhanced extraction
J. Contam. Hydrol.
(2002) Analysis of the steam injection at the Visalia Superfund Project with fully compositional nonisothermal finite difference simulations
J. Hazard. Mater.
(2002)Spectrophotometric study of spontaneous disproportionation of superoxide anion radical and sensitive direct assay for superoxide dismutase
J. Biol. Chem.
(1976)- et al.
Oxidation behavior of aqueous contaminants in the presence of hydrogen peroxide and filter media
J. Hazard. Mater.
(1995) - et al.
A controlled field experiment on groundwater contamination by a multicomponent DNAPL: creation of the emplaced-source and overview of dissolved plume development
J. Contam. Hydrol.
(2001) - et al.
The kinetics of decomposition of hydrogen peroxide in the presence of ethylenediaminetetraacetatoiron(III) complex
Inorg. Chim. Acta
(1982) - et al.
Laboratory and controlled field experiments using potassium permanganate to remediate trichloroethylene and perchloroethylene DNAPLs in porous media
J. Contam. Hydrol.
(1998)
In-situ oxidation of trichloroethene by permanganate: effects on porous medium hydraulic properties
J. Contam. Hydrol.
The effect of sorption on the oxidation of polychlorinated biphenyls (PCBs) by hydroxyl radical
Water Res.
Phase-transfer catalysis applied to the oxidation of non-aqueous phase trichloroethylene by potassium permanganate
J. Contam. Hydrol.
Evaluation of iron catalysts for the Fenton-like remediation of diesel-contaminated soils
J. Hazard. Mater.
Chemical oxidation of chlorinated non-aqueous phase liquid by hydrogen peroxide in natural sand systems
J. Hazard. Mater.
Reactivity of HO2/O2− radicals in aqueous solution
J. Phys. Chem. Ref. Data
Sorption kinetics of organic chemicals: evaluation of gas-purge and miscible-displacement techniques
Environ. Sci. Technol.
Critical review of rate constants for reactions of hydrated electrons, hydrogen atoms and hydroxyl radicals (•OH/•O−) in aqueous solution
J. Phys. Chem. Ref. Data
Alkali-induced generation of superoxide and hydroxyl radicals from aqueous hydrogen peroxide solution
Z. Phys. Chem.
Catalytic decomposition of hydrogen peroxide by Fe(III) in homogeneous aqueous solution: mechanism and kinetic modeling
Environ. Sci. Technol.
The factors determining nucleophilic reactivities
J. Am. Chem. Soc.
Kinetic and structural investigations of [FeIII(edta)]-[edta = ethylenediaminetetra-acetate(4-)] catalysed decomposition of hydrogen peroxide
J. Chem. Soc. Dalton Trans.
Rate constants for reaction of hydroxyl radicals with several drinking water contaminants
Environ. Sci. Technol.
Pilot-scale destruction of TNT, RDX, and HMX on contaminated soils using subcritical water
Environ. Sci. Technol.
Remediation of DNAPL pools using dense brine barrier strategies
Environ. Sci. Technol.
Cited by (65)
Toward rapid reduction of carbon tetrachloride in water by zero-valent aluminum/persulfate system
2022, ChemosphereCitation Excerpt :O2•- can react with halogenated organic compounds such as carbon tetrachloride, trichloroethylene, perchloroethylene, polychlorinated biphenyls and perfluoro caprylic acid (Smith et al., 2004; Watts and Teel, 2005). Unfortunately, O2•- has a very short lifetime in the aqueous phase (Hayyan et al., 2016) and very low reactivity with organic matter in the aqueous solution (Smith et al., 2006). Some scholars activated PS to degrade CT in aqueous solution at 50 °C and proved that O2•- was the main active species to degrade CT (Xu et al., 2015).
MnO<inf>2</inf> generation mechanisms in the presence of phase transfer catalyst enhanced trichloroethene oxidation by permanganate
2022, Process Safety and Environmental Protection