Oxidation Of PCE Research Articles

Surfactant-enhanced in-situ oxidation of DNAPL source zone: Experiments and numerical modeling

In this study we investigate the synergetic effects of combining surfactant-enhanced dissolution with in-situ oxidation of a pool-dominated PCE DNAPL source zone entrapped in porous media. Flow cell flushing experiments packed with silica sand and natural calcareous soil were conducted with a surfactant (Tween 80) and permanganate (MnO4−) used as dissolution and oxidation agents, respectively. The resultant breakthrough curves exhibited a multiple step behavior with mass removal controlled in the latter stages by the less-accessible DNAPL mass. DNAPL spatial architecture, flow-field heterogeneity, and flushing solution all influenced the remediation effort. When taking into account both the surfactant-enhanced dissolution and permanganate oxidation processes, mass-flux reduction/mass-removal behavior relationships indicated that the inclusion of oxidation in the remediation scheme delayed the drop in mass flux from the source zone, leading to improved DNAPL removal efficiency. Numerical modeling was also performed to further evaluate the efficacy of the surfactant-enhanced chemical oxidation of DNAPL PCE with permanganate. The system of reaction equations available in the multiphase flow simulator UTCHEM were adapted to simulate the chemical oxidation process in the presence of a surfactant. The model results yield lower oxidation reaction rate constants in the presence of Tween 80, indicating that Tween 80 can interfere with the reaction rate. However, the increase in the solubility of PCE in the presence of Tween 80 more than compensates for the decrease in reaction rate constant. Overall, for Tween 80/MnO4− applied at sufficient dosages, more efficient DNAPL zone remediation was achieved compared to surfactant flushing or permanganate oxidation alone.

Enhanced oxidation of tetrachloroethylene by Fenton reaction during interaction between nano-hematite and glutathione

The enhancement of oxidation of tetrachloroethylene (PCE) by the redox interaction between nano-hematite (nano-Fe2O3) and glutathione(GSH) was investigated. This study revealed the oxidation of PCE by the nano-Fe2O3-GSH occurred via Fenton-like reaction to initiate the formation of OH• and O2‾• radicals. The oxidation kinetic of PCE by the nano-Fe2O3-GSH was enhanced by 600 times greater (0.014 ± 0.003 hr−1) than that by the nano-Fe2O3 alone (0.00023 ± 0.00008 hr−1). The GSH played an important role as the catalyst to enhance redox reaction of Fe3+ to Fe2+ and promoted the formation of OH• and O2‾• radicals at netural and alkaline conditions. The reactivity of GSH was significantly increased at alkaline condition due to the high nucleophilicity of -SH. PCE was completely transformed to oxalic acid in the nano-Fe2O3-GSH suspension. This study provides new knowledge on the redox interaction between nano-Fe2O3 and GSH as a significant reaction mechanism to enhance the oxidation of PCE.

Enhancement effects of reducing agents on the degradation of tetrachloroethene in the Fe(II)/Fe(III) catalyzed percarbonate system

In this study, the effects of reducing agents on the degradation of tetrachloroethene (PCE) were investigated in the Fe(II)/Fe(III) catalyzed sodium percarbonate (SPC) system. The addition of reducing agents, including hydroxylamine hydrochloride, sodium sulfite, ascorbic acid and sodium ascorbate, accelerated the Fe(III)/Fe(II) redox cycle, leading to a relatively steady Fe(II) concentration and higher production of free radicals. This, in turn, resulted in enhanced PCE oxidation by SPC, with almost complete PCE removal obtained for appropriate Fe and SPC concentrations. The chemical probe tests, using nitrobenzene and carbon tetrachloride, demonstrated that HO was the predominant radical in the system and that O2− played a minor role, which was further confirmed by the results of electron spin resonance measurements. PCE degradation decreased significantly with the addition of isopropanol, a HO scavenger, supporting the hypothesis that HO was primarily responsible for PCE degradation. It is noteworthy that Cl− release was slightly delayed in the first 20min, indicating that intermediate products were produced. However, these intermediates were further degraded, resulting in the complete conversion of PCE to CO2. In conclusion, the use of reducing agents to enhance Fe(II)/Fe(III) catalyzed SPC oxidation appears to be a promising approach for the rapid degradation of organic contaminants in groundwater.

Lowering temperature to increase chemical oxidation efficiency: The effect of temperature on permanganate oxidation rates of five types of well defined organic matter, two natural soils, and three pure phase products

In situ chemical oxidation (ISCO) is a soil remediation technique to remove organic pollutants from soil and groundwater with oxidants, like KMnO4. However, also natural organic compounds in soils are being oxidized, which makes the technique less efficient. Laboratory experiments were performed to investigate the influence of temperature on this efficiency, through its effect on the relative oxidation rates – by permanganate – of natural organic compounds and organic pollutants at 16 and 15°C. Specific types of organic matter used were cellulose, oak wood, anthracite, reed – and forest peat, in addition to two natural soils. Dense Non-Aqueous Phase Liquid-tetrachloroethene (DNAPL-PCE), DNAPL trichloroethene (DNAPL-TCE) and a mixture of DNAPL-PCE, -TCE and -hexachlorobutadiene were tested as pollutants.Compared to 16°C, oxidation was slower at 5°C for the specific types of organic matter and the natural soils, with exception of anthracite, which was unreactive. The oxidation rate of DNAPL TCE was lower at 5°C too. However, at this temperature oxidation was fast, implying that no competitive loss to natural organic compounds will be expected in field applications by lowering temperature. Oxidation of DNAPL-PCE and PCE in the mixture proceeded at equal rates at both temperatures, due to the dissolution rate as limiting factor. These results show that applying permanganate ISCO to DNAPL contamination at lower temperatures will limit the oxidation of natural organic matter, without substantially affecting the oxidation rate of the contaminant. This will make such remediation more effective and sustainable in view of protecting natural soil quality.

Time series geophysical monitoring of permanganate injections and in situ chemical oxidation of PCE, OU1 area, Savage Superfund Site, Milford, NH, USA

In situ chemical oxidation (ISCO) treatment with sodium permanganate, an electrically conductive oxidant, provides a strong electrical signal for tracking of injectate transport using time series geophysical surveys including direct current (DC) resistivity and electromagnetic (EM) methods. Effective remediation is dependent upon placing the oxidant in close contact with the contaminated aquifer. Therefore, monitoring tools that provide enhanced tracking capability of the injectate offer considerable benefit to guide subsequent ISCO injections. Time-series geophysical surveys were performed at a superfund site in New Hampshire, USA over a one-year period to identify temporal changes in the bulk electrical conductivity of a tetrachloroethylene (PCE; also called tetrachloroethene) contaminated, glacially deposited aquifer due to the injection of sodium permanganate. The ISCO treatment involved a series of pulse injections of sodium permanganate from multiple injection wells within a contained area of the aquifer. After the initial injection, the permanganate was allowed to disperse under ambient groundwater velocities. Time series geophysical surveys identified the downward sinking and pooling of the sodium permanganate atop of the underlying till or bedrock surface caused by density-driven flow, and the limited horizontal spread of the sodium permanganate in the shallow parts of the aquifer during this injection period. When coupled with conventional monitoring, the surveys allowed for an assessment of ISCO treatment effectiveness in targeting the PCE plume and helped target areas for subsequent treatment.

PCE Oxidation by Sodium Persulfate in the Presence of Solids

Batch reactor experiments were performed to determine the effects of solids on the oxidation of tetracholoroethylene (PCE) by sodium persulfate in aqueous solution. Based on the rates of PCE degradation and chloride formation, PCE oxidation by heat-activated sodium persulfate at 50 °C in the presence of solids ranged from no detectable oxidation of PCE to the levels observed in water-only reactors. Repeated doses of sodium persulfate, undertaken to overcome the inherent solids oxidant demand, improved the rate and extent of PCE oxidation in reactors containing reference solids; however, no improvement was observed in reactors containing field soils. Additionally, no improvements in PCE oxidation were observed after pretreating Great Lakes and Appling soils with ca. 15 g/kg of sodium persulfate or 30% hydrogen peroxide to remove oxidizable fractions, or acetic acid to remove the carbonate fraction. Based on these results, in situ treatment of Great Lakes and Appling soils with heat-activated sodium persulfate is not anticipated to result in substantial PCE oxidation, while in situ treatment of Fort Lewis soils is anticipated to result in PCE oxidation. This work demonstrates the need to perform soil-specific contaminant treatability tests rather than soil oxidant demand tests when determining oxidant dosage requirements.

Phosgene-Free Photocatalytic Degradation of TCE and PCE Vapors with Au/TiO2

Photocatalytic oxidation of trichloroethylene (TCE) and tetrachloroethylene (PCE) in air had been carried out with TiO2 film alone and Au/TiO2 film. On the TiO2 film TCE and PCE were converted mainly into toxic COCl2, while COCl2 free TEC and PCE oxidation could be achieved with Au/TiO2.

Compatibility of Polymers and Chemical Oxidants for Enhanced Groundwater Remediation

Polymer floods provide a promising method to more effectively deliver conventional groundwater treatment agents to organic contaminants distributed within heterogeneous aquifer systems. Combinations of nontoxic polymers (xanthan and hydrolyzed polyacrylamide) and common chemical oxidants (potassium permanganate and sodium persulfate) were investigated to determine the suitability of these mixtures for polymer-enhanced in situ chemical oxidation applications. Oxidant demand and solution viscosity were utilized as initial measures of chemical compatibility. After 72 h of reaction with both test oxidants, solution viscosities in mixtures containing hydrolyzed polyacrylamide were decreased by more than 90% (final viscosities approximately 2 cP), similar to the 95% viscosity loss (final viscosities approximately 1 cP, near that of water) observed in xanthan/persulfate experiments. In contrast, xanthan solutions exposed to potassium permanganate preserved 60-95% of initial viscosity after 72 h. Permanganate depletion in xanthan-containing experiments ranged from 2% to 24% over the same test period. Although oxidant consumption in xanthan/permanganate solutions appeared to be correlated with increasing xanthan concentrations, solutions of up to 2000 mg/L xanthan did not inhibit permanganate from oxidizing a dissolved-phase test contaminant (tetrachloroethene, PCE) in xanthan solution. These advantageous characteristics (high viscosity retention, moderate oxidant demand, and lack of competitive effects on PCE oxidation rate) render xanthan/permanganate the most compatible polymer/oxidant combination of those tested for remediation by polymer-enhanced chemical oxidation.

Role of Diffusion in Chemical Oxidation of PCE in a Dual Permeability System

The effect of in situ chemical oxidation (ISCO) with permanganate (MnO4-) on tetrachloroethene (PCE) in a dual permeability system consisting of low permeability clay with high permeability sand lenses was investigated by two-dimensional laboratory experiments. The experiments imitate a field remediation at a former dry cleaning facility in Denmark. Results from laboratory experiments and field observations both show that after an application of MnO4- in the sand layer, the diffusion rate into the matrix is decreased due to reaction with PCE and the natural oxidant demand (NOD) related to the clayey till. A narrow but very efficient reaction zone is created in the clayey till. Initiallythe zone developed rapidlyfollowed by a slower expansion with time. PCE will counter diffuse into the reaction zone, where it will be degraded as long as MnO4- is present. A mass balance for the laboratory experiment revealed that the reaction between MnO4- and the clayey till was responsible for up to 90% of the total MnO4- consumption. Based on laboratory experiments, the high MnO4- consumption from reaction with clayey till appears to have been the limiting factor for the oxidation of PCE at the field site and is thus impairing the efficiency of ISCO as a remedy.

Calcium peroxide (CaO 2) for use in modified Fenton chemistry

The use of calcium peroxide (CaO 2) powder as a source of H 2O 2 to promote modified Fenton (MF) chemistry was studied. First, the rate of production and yield of H 2O 2 from CaO 2 dissolving in water at pH 6–9, and 12–13 (i.e., unbuffered CaO 2) was measured. The rate of CaO 2 dissolution increased as pH decreased, from 62 h for complete dissolution at pH 12–13 to only 4 h at pH 6. The yield of H 2O 2 also increased with decreasing pH, from zero at pH 12–13 to 82% at pH 6. The ability of CaO 2 to promote MF oxidation of PCE was demonstrated with a hydroxyl radical ( OH) scavenger (2-propanol) at pH 8. The scavenger inhibited PCE oxidation, but 97% of the PCE was oxidized without it. Release of Cl − showed that PCE was mineralized. Finally, PCE oxidation was compared with liquid H 2O 2 (pH 7) and with CaO 2 (pH 6, 7, 8, 9). Liquid H 2O 2 showed the lowest efficiency (mol H 2O 2 consumed/mol PCE oxidized) and the greatest temperature increase, disproportionation to O 2, and PCE volatilization. CaO 2 was a more efficient oxidant than liquid H 2O 2 at all pH values because it only releases H 2O 2 upon dissolution, reducing the loss to O 2 and volatilization. CaO 2 performed optimally at pH 8.

Volatile organic compounds (VOCs) removal over dual functional adsorbent/catalyst system

This study is focused on the elimination of tetrachloroethylene (PCE) and methylethylketone (MEK) by adsorption/catalytic oxidation in humid conditions using zeolites as adsorbent and catalyst. Adsorption experiments have led to the conclusion that HFAU(17) zeolite was a very efficient adsorbent for the removal of PCE and MEK. Furthermore, complete transformation of PCE into CO2 and HCl was achieved at 500°C over 1.2%Pt/HFAU(5). MEK was completely converted into CO2 at 220°C over 1%Pt/NaX, without formation of CO. Formation of coke occurs during MEK oxidation reaction, especially over acid catalyst, and at low reaction temperature. Furthermore, it was pointed out that water has a negative effect on MEK conversion. Lastly, adsorption/catalytic oxidation of PCE and MEK was performed over a dual functional HFAU(17)-Pt/FAU adsorbent/catalyst system. The adsorption step was performed at 30°C with an HFAU(17) adsorbent, and the oxidation step was carried out at 450°C for PCE with 1.2%PtHFAU(5), and at 250°C for MEK transformation with 1%PtNaX. It appeared that the adsorbent-catalyst couple remains efficient for MEK transformation during successive adsorption/oxidation cycles.

Quantification of potassium permanganate consumption and PCE oxidation in subsurface materials

A series of laboratory scale batch slurry experiments were conducted in order to establish a data set for oxidant demand by sandy and clayey subsurface materials as well as to identify the reaction kinetic rates of permanganate (MnO 4 −) consumption and PCE oxidation as a function of the MnO 4 − concentration. The laboratory experiments were carried out with 31 sandy and clayey subsurface sediments from 12 Danish sites. The results show that the consumption of MnO 4 − by reaction with the sediment, termed the natural oxidant demand (NOD), is the primary reaction with regards to quantification of MnO 4 − consumption. Dissolved PCE in concentrations up to 100 mg/l in the sediments investigated is not a significant factor in the total MnO 4 − consumption. Consumption of MnO 4 − increases with an increasing initial MnO 4 − concentration. The sediment type is also important as NOD is (generally) higher in clayey than in sandy sediments for a given MnO 4 − concentration. For the different sediment types the typical NOD values are 0.5–2 g MnO 4 −/kg dry weight (dw) for glacial meltwater sand, 1–8 g MnO 4 −/kg dw for sandy till and 5–20 g MnO 4 −/kg dw for clayey till. The long term consumption of MnO 4 − and oxidation of PCE can not be described with a single rate constant, as the total MnO 4 − reduction is comprised of several different reactions with individual rates. During the initial hours of reaction, first order kinetics can be applied, where the short term first order rate constants for consumption of MnO 4 − and oxidation of PCE are 0.05–0.5 h − 1 and 0.5–4.5 h − 1 , respectively. The sediment does not act as an instantaneous sink for MnO 4 −. The consumption of MnO 4 − by reaction with the reactive species in the sediment is the result of several parallel reactions, during which the reaction between the contaminant and MnO 4 − also takes place. Hence, application of low MnO 4 − concentrations can cause partly oxidation of PCE, as the oxidant demand of the sediment does not need to be met fully before PCE is oxidised.

Effect of Fenton Reagent Dose on Coexisting Chemical and Microbial Oxidation in Soil

The ability of modified Fenton reactions to promote simultaneous chemical and biological oxidation in an artificially contaminated soil was studied in batch laboratory slurry reactors. Tetrachloroethene (PCE) and oxalate (OA) were used to distinguish chemical oxidation from aerobic heterotrophic metabolism. PCE was mineralized by Fenton reactions, but OA was not oxidized. Indigenous soil microorganisms did not degrade added PCE aerobically but readily assimilated OA. Fenton reactions were promoted at the natural soil pH (7.6) by adding H2O2 and Fe(III), with nitrilotriacetic acid (NTA) as a chelator, at a constant molar ratio of H2O2/Fe(III)/NTA of 50:1:1. The *OH-mediated mineralization of PCE was demonstrated by adding 2-propanol (an *OH scavenger), which inhibited PCE oxidation. In subsequent dosing studies, PCE oxidation served as an indicator of Fenton reactions, while OA assimilation, dissolved oxygen (DO) concentration, and heterotrophic plate counts were indicators of aerobic microbial activity. Increasing Fenton doses to 20 times that required to achieve 95% PCE oxidation only delayed OA assimilation by 500 min and reduced plate counts by 1.5 log units g(-1) soil. Results show that aerobic metabolism can coexist with Fenton oxidation in soils.

TiO2 Photocatalytic Oxidation of Butyraldehyde, Ethylbenzene and PCE in the Air through Concentric Reactors

AbstractNine glass concentric reactors (LD. from 19 to 94 mm) were constructed with a 4-watt UV lamp (1.5 cm O.D. × 11 cm length) located at the center. TiO

Evidence for Simultaneous Abiotic−Biotic Oxidations in a Microbial-Fenton's System

The conditions that support the simultaneous activity of hydroxyl radicals (OH.) and heterotrophic aerobic bacterial metabolism were investigated using two probe compounds: (1) tetrachloroethene (PCE) for the detection of OH. generated by an iron-nitrilotriacetic acid (Fe-NTA) catalyzed Fenton-like reaction and (2) oxalate (OA) for the detection of heterotrophic metabolism of Xanthobacter flavus. In the absence of the bacterium in the quasi-steady-state Fenton's system, only PCE oxidation was observed; conversely, only OA assimilation was found in non-Fenton's systems containing X. flavus. In combined Fenton's-microbial systems, loss of both probes was observed. PCE oxidation increased and heterotrophic assimilation of OA declined as a function of an increase in the quasi-steady-state H2O2 concentration. Central composite rotatable experimental designs were used to determine the conditions that provide maximum simultaneous abiotic-biotic oxidations, which were achieved with a biomass level of 10(9) CFU/mL, 4.5 mM H2O2, and 2.5 mM Fe-NTA. These results demonstrate that heterotrophic bacterial metabolism can occur in the presence of hydroxyl radicals. Such simultaneous abiotic-biotic oxidations may exist when H2O2 is injected into the subsurface as a microbial oxygen source or as a source of chemical oxidants. In addition, hybrid abiotic-biotic systems could be used for the treatment of waters containing biorefractory organic contaminants present in recycle water, cooling water, or industrial waste streams.

Geochemical reactions resulting from in situ oxidation of PCE-DNAPL by KMnO4 in a sandy aquifer.

Although the potential for KMnO4 to destroy chlorinated ethenes in situ was first recognized more than a decade ago, the geochemical processes that accompany the oxidation have not previously been examined. In this study, aqueous KMnO4 solutions (10-30 g/L) were injected into an unconfined sand aquifer contaminated by the dense non-aqueous-phase liquid (DNAPL) tetrachloroethylene (PCE). The effects of the injections were monitored using depth-specific, multilevel groundwater samplers, and continuous cores. Two distinct geochemical zones evolved within several days after injection. In one zone where DNAPL is present, reactions between KMnO4 and dissolved PCE resulted in the release of abundant chloride and hydrogen ions to the water. Calcite and dolomite dissolved, buffering the pH in the range of 5.8-6.5, releasing Ca, Mg, and CO2 to the pore water. In this zone, the aqueous Ca/Cl concentration ratio is close to 5:12, consistent with the following reaction for the oxidation of PCE in a carbonate-rich aquifer: 3C2Cl4 + 5CaCO3(s) + 4KMnO4 + 2H+ --> 11CO2 + 4MnO2(s) + H2O + 12Cl- + 5Ca2+ + 4K+. In addition to Mg from dolomite dissolution, increases in the concentration of Mg as well as Na may result from exchange with K at cation-exchange sites. In the second zone, where lesser amounts of PCE were present, KMnO4 persisted in the aquifer for more than 14 months, and the porewater pH increased graduallyto between 9 and 10 as a resultof reaction between KMnO4 and H2O. A small increase in SO4 concentrations in the zones invaded by KMnO4 suggests that KMnO4 injections caused oxidation of sulfide minerals. There are important benefits of carbonate mineral buffering during DNAPL remediation by in situ oxidation. In a carbonate-buffered system, Mn(VII) is reduced to Mn(IV) and is immobilized in the groundwater by precipitating as insoluble manganese oxide. Energy-dispersive X-ray spectroscopy analyses of the manganese oxide coatings on aquifer mineral grains have detected the impurities Al, Ca, Cl, Cu, Pb, P, K, Si, S, Ti, U, and Zn indicating that, similar to natural systems, precipitation of manganese oxide is accompanied by coprecipitation of other elements. In addition, the consumption of excess KMnO4 by reaction with reduced minerals such as magnetite will be minimized because the rates of these reactions increase with decreasing pH. Aquifer cores collected after the KMnO4 injections exhibit dark brown to black bands of manganese oxide reaction products in sand layers where DNAPL was originally present. Mineralogical investigations indicate that the manganese oxide coatings are uniformly distributed over the mineral grains. Observations of the coatings using transmission electron microscopy indicate that they are on the order of 1 microm thick, and consequently, the decrease in porosity through the formation of the coatings is negligible.

Advanced Oxidation Processes for Treating Groundwater Contaminated With TCE and PCE: Laboratory Studies

Oxidation of trichloroethylene (TCE) and tetrachloroethylene (PCE) with various dosages of ozone or ozone plus hydrogen peroxide was studied in laboratory experiments. The results show that hydrogen peroxide accelerates the oxidation of TCE and PCE by ozone. At peroxide‐to‐ozone dosage ratios of >0.7 (w/w), the process appears to be mass transfer limited. High levels of bicarbonate ion in the groundwater significantly decreased the efficiency of TCE and PCE removal by the ozone‐peroxide system, suggesting that softening prior to oxidation may improve the process.