RESUMEN
Catalyzed H2O2 propagations (CHP) is characterized by the most robust reactivity of any of the in situ chemical oxidation (ISCO) technologies because it generates the strong oxidant hydroxyl radical along with nucleophiles + reductants, such as superoxide radical. The most common groundwater contaminants, trichloroethylene (TCE) and perchloroethylene (PCE), were used as model contaminants in evaluating the effect of hydrogen peroxide (H2O2) dosage on contaminant destruction kinetics. Both TCE and PCE degradation rates increased with H2O2 dosages up to 0.1â¯M, and then decreased with higher H2O2 dosages. Parallel reactions conducted with the addition of the hydroxyl radical scavenger 2-propanol and the hydroxyl radical-specific probe nitrobenzene confirmed that hydroxyl radical is primarily responsible for TCE and PCE degradation; however, 5-20% of their degradation was attributed to a non-hydroxyl radical mechanism. Reactions conducted with the superoxide probe tetranitromethane showed that superoxide generation rates increased with increasing H2O2 doses. These results were confirmed by electron spin resonance spectroscopy. Therefore, the non-hydroxyl radical pathway for TCE and PCE degradation at H2O2 ≥0.5â¯M was likely via nucleophilic attack by superoxide. The results of this research demonstrate that contaminants present in the aqueous phase that are reactive with hydroxyl radical require only low doses of H2O2 (≤0.1â¯M), but subsurface systems contaminated with species not reactive with hydroxyl radical (e.g., carbon tetrachloride) require H2O2 concentrationsâ¯≥0.5â¯M.
Asunto(s)
Tetracloroetileno , Tricloroetileno , Catálisis , Peróxido de Hidrógeno , Radical Hidroxilo , Hierro , Oxidación-ReducciónRESUMEN
Sodium persulfate has become the most popular oxidant source for the in situ chemical oxidation (ISCO) treatment of organic contaminants in the subsurface. The most common persulfate activators, iron chelates and base, are often ineffective in initiating the generation of reactive oxygen species in field applications. In this study, glucose was investigated as a persulfate activator in systems containing varying concentrations of sodium hydroxide using nitrobenzene as a hydroxyl radical probe and hexachloroethane as a reductant + nucleophile probe. Glucose activation of persulfate increased as a function of sodium hydroxide addition, but was still effective at circumneutral pH regimes. Use of central composite rotatable experimental designs showed that hydroxyl radical and reductant + nucleophile generation rates increased as a function of persulfate at near-neutral pH regimes. Glucose activation of persulfate has the advantages over other activation pathways of more options and flexibility for effective process chemistry and of minimizing or eliminating the mass of sodium hydroxide added to the subsurface. The results of this research can be applied in the field by first evaluating glucose activation compared to base and iron chelate activation of persulfate in laboratory treatability studies.
Asunto(s)
Etano/análogos & derivados , Glucosa/química , Hidrocarburos Clorados/química , Nitrobencenos/química , Oxidantes/química , Compuestos de Sodio/química , Hidróxido de Sodio/química , Sulfatos/química , Restauración y Remediación Ambiental , Etano/química , Concentración de Iones de Hidrógeno , Radical Hidroxilo/química , Oxidación-ReducciónRESUMEN
The effect of six water quality constituents on wastewater effluent disinfection by tin oxide anodes (TOAs) was investigated in single cell laboratory reactors. Several concentrations of suspended solids, chemical oxygen demand (COD), alkalinity, ammonia-nitrogen, nitrite-nitrogen, and nitrate-nitrogen were added to media containing 106 total coliform bacteria mL-1. Current was applied through the TOAs, and coliform bacteria viability was analyzed over time. Over 99.9% inactivation of coliform bacteria was found over 15 min in TOA reactors. Concentrations of the six water quality constituents typical of concentrations found in wastewaters had no effect on TOA disinfection efficacy. The results of this research demonstrate that TOAs, which could potentially be powered by solar panels, have potential as a sustainable disinfection process compared to chlorine, ozone, and ultraviolet light.
Asunto(s)
Desinfección/métodos , Enterobacteriaceae/efectos de los fármacos , Viabilidad Microbiana/efectos de los fármacos , Compuestos de Estaño/farmacología , Aguas Residuales/química , Aguas Residuales/microbiología , Calidad del Agua , Análisis de la Demanda Biológica de Oxígeno , Cloro/farmacología , Electrodos , Enterobacteriaceae/fisiología , Humanos , Nitrógeno/química , Ozono/farmacología , Compuestos de Estaño/química , Rayos Ultravioleta , Microbiología del Agua , Purificación del Agua/métodosRESUMEN
The activation of peroxymonosulfate by iron (II), iron (III), and iron (III)-EDTA for in situ chemical oxidation (ISCO) was compared using nitrobenzene as a hydroxyl radical probe, anisole as a hydroxyl radical+sulfate radical probe, and hexachloroethane as a reductant+nucleophile probe. In addition, activated peroxymonosulfate was investigated for the treatment of the model groundwater contaminants perchloroethylene (PCE) and trichloroethylene (TCE). The relative activities of hydroxyl radical and sulfate radical in the degradation of the probe compounds and PCE and TCE were isolated using the radical scavengers tert-butanol and isopropanol. Iron (II), iron (III), and iron (III)-EDTA effectively activated peroxymonosulfate to generate hydroxyl radical and sulfate radical, but only a minimal flux of reductants or nucleophiles. Iron (III)-EDTA was a more effective activator than iron (II) and iron (III), and also provided a non-hydroxyl radical, non-sulfate radical degradation pathway. The contribution of sulfate radical relative to hydroxyl radical followed the order of anisole>>TCE>PCE >>nitrobenzene; i.e., sulfate radical was less dominant in the oxidation of more oxidized target compounds. Sulfate radical is often assumed to be the primary oxidant in activated peroxymonosulfate and persulfate systems, but the results of this research demonstrate that the reactivity of sulfate radical with the target compound must be considered before drawing such a conclusion.
Asunto(s)
Hierro/química , Peróxidos/química , Especies Reactivas de Oxígeno/química , Contaminantes Químicos del Agua/química , Ácido Edético/química , Etano/análogos & derivados , Etano/química , Agua Subterránea/química , Hidrocarburos Clorados/química , Radical Hidroxilo/química , Nitrobencenos/química , Oxidantes/química , Oxidación-Reducción , Sustancias Reductoras/química , Sulfatos , Tetracloroetileno/química , Tricloroetileno/química , Purificación del Agua/métodos , Alcohol terc-ButílicoRESUMEN
Total oxidant demand (TOD) is a parameter that is often measured during in situ chemical oxidation (ISCO) treatability studies. The importance of TOD is based on the concept that the oxidant demand created by soil organic matter and other reduced species must be overcome before contaminant oxidation can proceed. TOD testing was originally designed for permanganate ISCO, but has also recently been applied to activated persulfate ISCO. Recent studies have documented that phenoxides activate persulfate; because soil organic matter is rich in phenolic moieties, it may activate persulfate rather than simply exerting TOD. Therefore, the generation of reactive oxygen species was investigated in three soil horizons of varied soil organic carbon content over 5-day TOD testing. Hydroxyl radical may have been generated during TOD exertion, but was likely scavenged by soil organic matter. A high flux of reductants + nucleophiles (e.g. alkyl radicals + superoxide) was generated as TOD was exerted, resulting in the rapid destruction of the probe compound hexachloroethane and the common groundwater contaminant trichloroethylene (TCE). The results of this research document that, unlike permanganate TOD, contaminant destruction does occur as TOD is exerted in persulfate ISCO systems and is promoted by the activation of persulfate by soil organic matter. Future treatability studies for persulfate ISCO should consider contaminant destruction as TOD is exerted, and the potential for persulfate activation by soil organic matter.
Asunto(s)
Monitoreo del Ambiente/métodos , Oxidantes/química , Sulfatos/química , Etano/análogos & derivados , Etano/análisis , Agua Subterránea , Hidrocarburos Clorados/análisis , Radical Hidroxilo/química , Compuestos de Manganeso/análisis , Compuestos de Manganeso/química , Oxidación-Reducción , Óxidos/análisis , Óxidos/química , Fenol/análisis , Especies Reactivas de Oxígeno/química , Sustancias Reductoras/química , Suelo/química , Contaminantes del Suelo/análisis , Tricloroetileno/análisis , Tricloroetileno/químicaRESUMEN
In situ chemical oxidation (ISCO) has become a widely used technology for the remediation of soil and groundwater. Although peroxymonosulfate is not a common oxidant source for ISCO, its chemical structure is similar to the ISCO reagents hydrogen peroxide and persulfate, suggesting that peroxymonosulfate may have the beneficial properties of each of these oxidants. Peroxymonosulfate activation in the presence of subsurface minerals was examined as a basis for ISCO, and possible reactive species (hydroxyl radical, sulfate radical, and reductants+nucleophiles) generated in the mineral-activated peroxymonosulfate systems were investigated. Rates of peroxymonosulfate decomposition and generation rates of reactive species were studied in the presence of three iron oxides, one manganese oxide, and three soil fractions. The iron oxide hematite-activated peroxymonosulfate system most effectively degraded the hydroxyl radical probe nitrobenzene. Reductants+nucleophiles were not generated in mineral-activated peroxymonosulfate systems. Use of the probe compound anisole in conjunction with scavengers demonstrated that both sulfate radical and hydroxyl radical are generated in mineral-activated peroxymonosulfate systems. In order to confirm the activation of peroxymonosulfate by subsurface minerals, one natural soil and associated two soil fractions were evaluated as peroxymonosulfate catalysts. The natural soil did not effectively promote the generation of oxidants; however, the soil organic matter was found to promote the generation of reductants + nucleophiles. The results of this research show that peroxymonosulfate has potential as an oxidant source for ISCO applications, and would be most effective in treating halogenated contaminants when soil organic matter is present in the subsurface.
Asunto(s)
Minerales/química , Peróxidos/química , Suelo/química , Anisoles/química , Compuestos Férricos/química , Concentración de Iones de Hidrógeno , Radical Hidroxilo/química , Compuestos de Manganeso/química , Oxidantes/química , Oxidación-Reducción , Óxidos/química , Sustancias Reductoras/química , Contaminantes del Suelo/química , Sulfatos/químicaRESUMEN
Catalyzed H2O2 propagations (CHP) was studied to treat 1,1,1-trichloroethane (TCA) and 1,1-dichloroethane (DCA) dense nonaqueous phase liquids (DNAPLs) and to elucidate the reactive oxygen species responsible for their destruction. A TCA DNAPL was rapidly destroyed by CHP at a rate 3.5 times greater than its maximum rate of dissolution. Using systems that generate a single reactive oxygen species, the species responsible for TCA DNAPL destruction was found to be superoxide. Both hydroxyl radical and superoxide were responsible for the destruction of the DCA DNAPL. Both compounds were destroyed at equal rates in a mixed TCA/DCA DNAPL, which suggests that the rate of treatment is limited by a surface phenomenon at the DNAPL-water interface. The optimum pH for the destruction of TCA and DCA DNAPLs was near the pKa of 4.8 for perhydroxyl radical-superoxide systems. The results of this research demonsrate that TCA and DCA DNAPLs are effectively destroyed by CHP and that superoxide generation is necessary for effective TCA DNAPL destruction, while both hydroxyl radical and superoxide are necessary for effective DCA DNAPL destruction.
Asunto(s)
Dicloruros de Etileno/química , Peróxido de Hidrógeno/química , Radical Hidroxilo/química , Tricloroetanos/química , Contaminantes Químicos del Agua/química , Catálisis , Agua Subterránea/química , Oxidación-ReducciónRESUMEN
Antibiotics that enter the environment can present human and ecological health risks. An understanding of antibiotic hydrolysis rates is important for predicting their environmental persistence as biologically active contaminants. In this study, hydrolysis rates and Arrhenius constants were determined as a function of pH and temperature for two amphenicol (chloramphenicol and florfenicol) and two macrolide (spiramycin and tylosin) antibiotics. Antibiotic hydrolysis rates in pH 4-9 buffer solutions at 25°C, 50°C, and 60°C were quantified, and degradation products were characterized. All of the antibiotics tested remained stable and exhibited no observable hydrolysis under ambient conditions typical of aquatic ecosystems. Acid- and base-catalyzed hydrolysis occurred at elevated temperatures (50-60°C), and hydrolysis rates increased considerably below pH 5 and above pH 8. Hydrolysis rates also increased approximately 1.5- to 2.9-fold for each 10°C increase in temperature. Based on the degradation product masses found, the functional groups that underwent hydrolysis were alkyl fluoride, amide, and cyclic ester (lactone) moieties; some of the resultant degradation products may remain bioactive, but to a lesser extent than the parent compounds. The results of this research demonstrate that amphenicol and macrolide antibiotics persist in aquatic systems under ambient temperature and pH conditions typical of natural waters. Thus, these antibiotics may present a risk in aquatic ecosystems depending on the concentration present.
Asunto(s)
Antibacterianos/análisis , Cloranfenicol/análisis , Macrólidos/análisis , Espiramicina/análisis , Tianfenicol/análogos & derivados , Tilosina/análisis , Catálisis , Ecosistema , Concentración de Iones de Hidrógeno , Hidrólisis , Inhibidores de la Síntesis de la Proteína/análisis , Temperatura , Tianfenicol/análisis , Agua/química , Contaminantes Químicos del Agua/análisisRESUMEN
Soil and leaf litter are significant global sources of small oxidized volatile organic compounds, VOCs (e.g., methanol and acetaldehyde). They may also be significant sources of larger VOCs that could act as precursors to secondary organic aerosol (SOA) formation. To investigate this, soil and leaf litter samples were collected from the University of Idaho Experimental Forest and transported to the laboratory. There, the VOC emissions were characterized and used to drive SOA formation via dark, ozone-initiated reactions. Monoterpenes dominated the emission profile with emission rates as high as 228 µg-C m(-2) h(-1). The composition of the SOA produced was similar to biogenic SOA formed from oxidation of ponderosa pine emissions and α-pinene. Measured soil and litter monoterpene emission rates were compared with modeled canopy emissions. Results suggest surface soil and litter monoterpene emissions could range from 12 to 136% of canopy emissions in spring and fall. Thus, emissions from leaf litter may potentially extend the biogenic emissions season, contributing to significant organic aerosol formation in the spring and fall when reduced solar radiation and temperatures reduce emissions from living vegetation.
Asunto(s)
Aerosoles/análisis , Contaminantes Atmosféricos/análisis , Contaminación del Aire/análisis , Compuestos Orgánicos/análisis , Hojas de la Planta/química , Suelo/química , Bosques , Oxidación-Reducción , Estaciones del Año , Terpenos/análisis , Factores de Tiempo , Compuestos Orgánicos Volátiles/análisisRESUMEN
An understanding of antibiotic hydrolysis rates is important for predicting their environmental persistence. Hydrolysis rates and Arrhenius constants were determined as a function of pH and temperature for three common ß-lactam antibiotics, ampicillin, cefalotin, and cefoxitin. Antibiotic hydrolysis rates at pH4-9 at 25 °C, 50 °C, and 60 °C were quantified, and degradation products were identified. The three antibiotics hydrolyzed under ambient conditions (pH7 and 25 °C); half-lives ranged from 5.3 to 27 d. Base-catalyzed hydrolysis rates were significantly greater than acid-catalyzed and neutral pH hydrolysis rates. Hydrolysis rates increased 2.5- to 3.9-fold for a 10 °C increase in temperature. Based on the degradation product masses found, the likely functional groups that underwent hydrolysis were lactam, ester, carbamate, and amide moieties. Many of the proposed products resulting from the hydrolysis of ampicillin, cefalotin, and cefoxitin likely have reduced antimicrobial activity because many products contained a hydrated lactam ring. The results of this research demonstrate that ß-lactam antibiotics hydrolyze under ambient pH and temperature conditions. Degradation of ß-lactam antibiotics will likely occur over several weeks in most surface waters and over several days in more alkaline systems.
Asunto(s)
Ampicilina/metabolismo , Antibacterianos/metabolismo , Cefoxitina/metabolismo , Cefalotina/metabolismo , Ampicilina/química , Antibacterianos/química , Cefoxitina/química , Cefalotina/química , Cromatografía Líquida de Alta Presión , Concentración de Iones de Hidrógeno , Hidrólisis , TemperaturaRESUMEN
The impacts of four common animal husbandry antibiotics (ampicillin, florfenicol, sulfamethazine, and tylosin) on anaerobic digestion (AD) treatment efficiency and the potential for antibiotic degradation during digestion were evaluated. Sulfamethazine and ampicillin exhibited no impact on total biogas production up to 280 and 350 mg/L, respectively, although ampicillin inhibited biogas production rates during early stages of AD. Tylosin reduced biogas production by 10-38% between 130 and 913 mg/L. Florfenicol reduced biogas by ≈ 5%, 40% and 75% at 6.4, 36 and 210 mg/L, respectively. These antibiotic concentrations are higher than commonly seen for mixed feedlot manure, so impacts on full scale AD should be minimal. Antibiotic degradation products were found, confirming AD effectively degraded ampicillin, florfenicol, and tylosin, although some products were persistent throughout the process. Contamination of AD solid and liquid effluents with sulfamethazine and antibiotic transformation products from florfenicol and tylosin could present an environmental concern.
Asunto(s)
Antibacterianos/farmacología , Biocombustibles , Sulfametazina/farmacología , Tianfenicol/análogos & derivados , Tilosina/farmacología , Ampicilina/química , Ampicilina/farmacología , Anaerobiosis/efectos de los fármacos , Animales , Antibacterianos/química , Reactores Biológicos , Bovinos , Clorofenoles/química , Cromatografía Liquida , Estiércol , Espectrometría de Masa por Ionización de Electrospray , Sulfametazina/química , Tianfenicol/química , Tianfenicol/farmacología , Tilosina/químicaRESUMEN
The water quality parameters nitrate-nitrogen, dissolved organic carbon, and suspended solids were correlated with photodegradation rates of the herbicides atrazine and 2,4-D in samples collected from four sites in the Columbia River Basin, Washington, USA. Surface water samples were collected in May, July, and October 2010 and analyzed for the water quality parameters. Photolysis rates for the two herbicides in the surface water samples were then evaluated under a xenon arc lamp. Photolysis rates of atrazine and 2,4-D were similar with rate constants averaging 0.025 h(-1) for atrazine and 0.039 h(-1) for 2,4-D. Based on multiple regression analysis, nitrate-nitrogen was the primary predictor of photolysis for both atrazine and 2,4-D, with dissolved organic carbon also a predictor for some sites. However, at sites where suspended solids concentrations were elevated, photolysis rates of the two herbicides were controlled by the suspended solids concentration. The results of this research provide a basis for evaluating and predicting herbicide photolysis rates in shallow surface waters.
Asunto(s)
Herbicidas/análisis , Fotólisis , Ríos/química , Contaminantes Químicos del Agua/análisis , Monitoreo del Ambiente , Washingtón , Calidad del AguaRESUMEN
The activation of persulfate by phenols was investigated to further the understanding of persulfate chemistry for in situ chemical oxidation (ISCO). Phenol (pKa = 10.0) activated persulfate at pH 12 but not at pH 8, suggesting activation occurred only via the phenoxide form. Evaluation of the phenoxide activation mechanism was complicated by the concurrent activation of persulfate by hydroperoxide anion, which is generated by the base catalyzed hydrolysis of persulfate. Therefore, phenoxide activation was investigated using pentachlorophenoxide at pH 8.3, midway between the pKa of pentachlorophenol (pKa = 4.8) and that of hydrogen peroxide (pKa = 11.8). Of the two possible mechanisms for phenoxide activation of persulfate (reduction or nucleophilic attack) the results were consistent with reduction of persulfate by phenoxide with oxidation of the phenoxide. The concentration of phenoxide required for maximum persulfate activation was low (1 mM). The results of this research document that phenoxides activate persulfate via reduction; phenolic moieties ubiquitous to soil organic matter in the subsurface may have a significant role in the activation of persulfate during its injection into the subsurface for ISCO. Furthermore, the results provide the foundation for activation of persulfate by other organic anions without the toxicity of phenols, such as keto acids.
Asunto(s)
Fenoles/química , Sulfatos/química , Peróxido de Hidrógeno/química , Concentración de Iones de Hidrógeno , Pentaclorofenol/química , Contaminantes del Suelo/química , Relación Estructura-ActividadRESUMEN
The use of tin oxide anodes (TOAs) has been proposed for the disinfection of wastewater effluents and concurrent treatment of emerging contaminants. The common water quality constituents suspended solids, chemical oxygen demand (COD), alkalinity, ammonia-nitrogen, nitrite-nitrogen, and nitrate-nitrogen were investigated for their effect on oxidation performance by TOAs. Relative oxidant generation rates were not affected by increasing concentrations of suspended solids, COD, alkalinity, ammonia-nitrogen, or nitrate-nitrogen. Although nitrite-nitrogen did compete for oxidants generated by TOAs, nitrite is not usually present in oxygenated effluents. Chemical oxygen demand, ammonia, and nitrite were oxidized in the TOA systems, primarily through a non-hydroxyl radical mechanism. This research demonstrates that a majority of the common water quality constituents did not negatively affect TOA oxidation performance. Tin oxide anodes represent a potentially low cost and low maintenance option for single-step disinfection and treatment of emerging contaminants in wastewater effluents.
Asunto(s)
Desinfección/métodos , Compuestos de Nitrógeno/química , Compuestos de Estaño/química , Análisis de la Demanda Biológica de Oxígeno , Electrodos , Compuestos de Nitrógeno/análisis , Oxidación-Reducción , Aguas Residuales/análisis , Calidad del AguaRESUMEN
Deicers currently used for aircraft deicing, including ethylene glycol and propylene glycol, pose significant threats to surface waters, as a result of high biochemical oxygen demand (BOD) and toxicity to aquatic organisms. Oxidized starch may provide a less toxic deicer with lower BOD. The freezing point depression of starch formulations oxidized using hydrogen peroxide and catalysts (i.e., catalyzed hydrogen peroxide [H2O2] propagations-CHP) was 28 degrees C, and viscosities similar to those of commercial deicers were achieved after post-treatment with granular activated carbon. The most effective oxidized starch formulation exerted a 5-day BOD up to 6 times lower than glycol deicers (103 versus 400 to 800 g O2/L). Toxicity to Ceriodaphnia dubia for this formulation (48-hour lethal concentration, 50% [LC50] of 2.73 g/L) was greater than pure propylene glycol (13.1 g/ L), but lower than propylene glycol deicer formulations (1.02 g/L). Organic acids were identified by gas chromatography/mass spectrometry as the primary constituents in the oxidized starch solution. The proposed deicing system would provide effective deicing while exerting minimal environmental effects (e.g., lower toxicity to aquatic organisms and lower BOD). Furthermore, these deicers could be made from waste starch, promoting sustainability.
Asunto(s)
Aeronaves , Conservación de los Recursos Naturales , Congelación , Hielo , SolucionesRESUMEN
The potential for 13 naturally occurring minerals to mediate the decomposition of persulfate and generate a range of reactive oxygen species was investigated to provide fundamental information on activation mechanisms when persulfate is used for in situ chemical oxidation (ISCO). Only four of the minerals (cobaltite, ilmenite, pyrite, and siderite) promoted the decomposition of persulfate more rapidly than persulfate-deionized water control systems. The other nine minerals decomposed persulfate at the same rate or more slowly than the control systems. Mineral-mediated persulfate activation was conducted with the addition of one of three probe compounds to detect the generation of reactive oxygen species: anisole (sulfate+hydroxyl radical), nitrobenzene (hydroxyl radical), and hexachloroethane (reductants and nucleophiles). The reduced mineral pyrite promoted rapid generation of sulfate+hydroxyl radical. However, the remainder of the minerals provided minimal potential for the generation of reactive oxygen species. The results of this research demonstrate that the majority of naturally occurring trace minerals do not activate persulfate to generate reactive oxygen species, and other mechanisms of activation are necessary to promote contaminant destruction in the subsurface during persulfate ISCO.
Asunto(s)
Restauración y Remediación Ambiental/métodos , Compuestos de Sodio/análisis , Contaminantes del Suelo/análisis , Sulfatos/análisis , Oligoelementos/química , Oxidación-Reducción , Especies Reactivas de Oxígeno/química , Factores de TiempoRESUMEN
Two surface soils contaminated with polychlorinated biphenyls (PCBs) collected from Superfund sites in the New England region of the United States, Fletcher Paints and Merrimack Industrial Metals, were evaluated for field treatment at the bench level using catalyzed H(2)O(2) propagations (CHP-modified Fenton's reagent). The two soils were first evaluated for the potential for in situ treatment based on two criteria: (1) temperature (< 40 °C after CHP reagent addition), and (2) hydrogen peroxide longevity (> 24h). In situ CHP remediation was more applicable to the Fletcher soil, while the Merrimack soil was better suited to ex situ treatment based on temperature increases and hydrogen peroxide lifetimes. Using the highest hydrogen peroxide concentrations appropriate for in situ treatment in each soil, PCB destruction was 94 % in the Fletcher soil but only 48% in the Merrimack soil. However, 98% PCB destruction was achieved in the Merrimack soil using conditions more applicable to ex situ treatment (higher hydrogen peroxide concentrations with temperatures > 40 °C). Analysis of degradation products by gas chromatography/mass spectroscopy showed no detectable chlorinated degradation products, suggesting that the products of PCB oxidation were rapidly dechlorinated and degraded. The results of this research document that the two PCB-contaminated soils studied can be effectively treated using aggressive CHP conditions, and that such a detailed bench study provides important information before implementing field treatment.
Asunto(s)
Restauración y Remediación Ambiental/métodos , Peróxido de Hidrógeno/química , Bifenilos Policlorados/química , Contaminantes del Suelo/química , Concentración de Iones de Hidrógeno , Bifenilos Policlorados/análisis , Suelo/química , Contaminantes del Suelo/análisisRESUMEN
Rapid hydrogen peroxide decomposition is the primary limitation of catalyzed H(2)O(2) propagations in situ chemical oxidation (CHP ISCO) remediation of the subsurface. Two stabilizers of hydrogen peroxide, citrate and phytate, were investigated for their effectiveness in one-dimensional columns of iron oxide-coated and manganese oxide-coated sand. Hydrogen peroxide (5%) with and without 25 mM citrate or phytate was applied to the columns and samples were collected at 8 ports spaced 13 cm apart. Citrate was not an effective stabilizer for hydrogen peroxide in iron-coated sand; however, phytate was highly effective, increasing hydrogen peroxide residuals two orders of magnitude over unstabilized hydrogen peroxide. Both citrate and phytate were effective stabilizers for manganese-coated sand, increasing hydrogen peroxide residuals by four-fold over unstabilized hydrogen peroxide. Phytate and citrate did not degrade and were not retarded in the sand columns; furthermore, the addition of the stabilizers increased column flow rates relative to unstabilized columns. These results demonstrate that citrate and phytate are effective stabilizers of hydrogen peroxide under the dynamic conditions of one-dimensional columns, and suggest that citrate and phytate can be added to hydrogen peroxide before injection to the subsurface as an effective means for increasing the radius of influence of CHP ISCO.
Asunto(s)
Ácido Cítrico/química , Restauración y Remediación Ambiental/métodos , Peróxido de Hidrógeno/química , Ácido Fítico/química , Catálisis , Hierro/química , Manganeso/química , Oxidación-Reducción , Dióxido de Silicio/químicaRESUMEN
The possibility of simultaneous activity of superoxide-mediated transformations and heterotrophic aerobic bacterial metabolism was investigated in catalyzed H(2)O(2) propagations (CHP; i.e., modified Fenton's reagent) systems containing Escherichia coli. Two probe compounds were used: glucose for the detection of heterotrophic metabolism of E. coli, and tetrachloromethane (CCl(4)) for the detection of superoxide generated in a MnO(2)-catalyzed CHP system. In the MnO(2)-catalyzed CHP system without bacteria, only CCl(4) loss was observed; in contrast, only glucose degradation occurred E. coli systems without CHP reagents. In combined microbial-MnO(2) CHP reactions, loss of both probes was observed. Glucose assimilation decreased and CCl(4) transformation increased as a function of H(2)O(2) concentration. Central composite rotatable experimental designs were used to determine that the conditions providing maximum simultaneous abiotic-biotic reactions were a biomass level of 10(9)CFU/mL, 0.5mM H(2)O(2), and 0.5 g MnO(2). These results demonstrate that bacterial metabolism can occur in the presence of superoxide-mediated transformations. Such coexisting reactions may occur when H(2)O(2) is injected into MnO(2)-rich regions of the subsurface as a microbial oxygen source or for in situ oxidation; however, process control of such coexisting transformations may be difficult to achieve in the subsurface due to heterogeneity. Alternatively, hybrid abiotic reduction-biotic oxidation systems could be used for the treatment of industrial effluents or dilute solvent wastes that contain traces of highly halogenated compounds.
Asunto(s)
Restauración y Remediación Ambiental/métodos , Escherichia coli/metabolismo , Compuestos de Manganeso/química , Óxidos/química , Biocatálisis , Biodegradación Ambiental , Tetracloruro de Carbono/química , Tetracloruro de Carbono/metabolismo , Catálisis , Contaminantes Ambientales/química , Contaminantes Ambientales/metabolismo , Glucosa/química , Glucosa/metabolismo , Peróxido de Hidrógeno/química , Peróxido de Hidrógeno/metabolismo , Hierro , Compuestos de Manganeso/metabolismo , Oxidación-Reducción , Óxidos/metabolismoRESUMEN
Base is the most commonly used activator of persulfate for the treatment of contaminated groundwater by in situ chemical oxidation (ISCO). A mechanism for the base activation of persulfate is proposed involving the base-catalyzed hydrolysis of persulfate to hydroperoxide anion and sulfate followed by the reduction of another persulfate molecule by hydroperoxide. Reduction by hydroperoxide decomposes persulfate into sulfate radical and sulfate anion, and hydroperoxide is oxidized to superoxide. The base-catalyzed hydrolysis of persulfate was supported by kinetic analyses of persulfate decomposition at various base:persulfate molar ratios and an increased rate of persulfate decomposition in D(2)O vs H(2)O. Stoichiometric analyses confirmed that hydroperoxide reacts with persulfate in a 1:1 molar ratio. Addition of hydroperoxide to basic persulfate systems resulted in rapid decomposition of the hydroperoxide and persulfate and decomposition of the superoxide probe hexachloroethane. The presence of superoxide was confirmed with scavenging by Cu(II). Electron spin resonance spectroscopy confirmed the generation of sulfate radical, hydroxyl radical, and superoxide. The results of this research are consistent with the widespread reactivity reported for base-activated persulfate when it is used for ISCO.