Trichloroethylene In Solution Research Articles

Improving the Pervaporation Performance of PDMS Membranes for Trichloroethylene by Incorporating Silane-Modified ZSM-5 Zeolite.

The hydrophobic nature of inorganic zeolite particles plays a crucial role in the efficacy of mixed matrix membranes (MMMs) for the separation of trichloroethylene (TCE) through pervaporation. This study presents a novel approach to further augment the hydrophobicity of ZSM-5. The ZSM-5 zeolite molecular sieve was subjected to modification using three different silane coupling agents, namely, n-octyltriethoxysilane (OTES), γ-methacryloxypropyltrimethoxysilane (KH-570), and γ-aminopropyltriethoxysilane (KH-550). The water contact angles of the resulting OTES@ZSM-5, KH-570@ZSM-5, and KH-550@ZSM-5 particles exhibited significant increases from 97.2° to 112.8°, 109.1°, and 102.7°, respectively, thereby indicating a notable enhancement in hydrophobicity. Subsequently, mixed matrix membranes (MMMs) were fabricated by incorporating the aforementioned silane-modified ZSM-5 particles into polydimethylsiloxane (PDMS), leading to a considerable improvement in the adsorption selectivity of these membranes towards trichloroethylene (TCE). The findings indicate that the PDMS membrane with a 20 wt.% OTES@ZSM-5 particle loading exhibits superior pervaporation performance. When subjected to a temperature of 30 °C, flow rate of 100 mL/min, and vacuum of 30 Kpa, the separation factor and total flux of a 3 × 10-7 wt.% TCE solution reach 328 and 155 gm-2·h-1, respectively. In comparison to the unmodified ZSM-5/PDMS membrane, the separation factor demonstrates a 41% increase, while the TCE flux experiences a 6% increase. Consequently, this approach effectively enhances the pervaporation separation capabilities of the PDMS membrane for TCE.

Hydrogen Isotope Exchange between Trichloroethene and Water under Mild Environmental Conditions─Implications for the Use of Hydrogen CSIA in Contaminated Site Assessment

Trichloroethylene (TCE) is a key legacy environmental contaminant and a major target for contaminant remediation projects. Hydrogen compound-specific isotope analysis (CSIA) of halocarbons is a relatively recent technique, predominantly used as a line of evidence for apportionment of TCE sources. To date, no published data addressed the potential for hydrogen exchange between TCE and hydroxide in a water solution under typical groundwater pH conditions. In this study, we determined the pH- and temperature-dependent rates of exchange in controlled experiments to constrain the scope of applications of hydrogen CSIA at field sites contaminated by TCE. Relatively high rates of the exchange were associated with above-neutral pH typical of carbonate aquifers (half-lives of years to decades) and slower, but not negligible, rates were associated with sub-neutral pH. Hydrogen exchange alters the hydrogen isotope composition of TCE in solution, masking initial source signatures or degradation signatures over environmentally relevant time scales. In effect, the TCE–water exchange restricts the classical applications of hydrogen CSIA data to a subset of distinctly acidic environments. On the other hand, as the rates of the exchange can be predicted for specific combinations of pH and temperature, the process could be potentially utilized in age-dating of TCE contamination.

Trichloroethylene remediation using zero-valent iron with kaolin clay, activated carbon and bacteria

Nanoscale particles of zero-valent iron were used to form a permeable reactive barrier whose performance in dechlorinating a solution of trichloroethylene was compared with that of a barrier formed from limestone. The iron was combined with kaolin by calcination. The test liquid contained sewage sludge, and also added NH4Cl and KH2PO4. The average removal rates of trichloroethylene and phosphorus over 365 days both exceeded 94%. Chemical oxygen demand was reduced by 92% and ammonium nitrogen by 43.6%. All were significantly greater than the removals with the limestone barrier. The ceramsite barrier retained 85% of its effectiveness even after 365 days of use. Dechloromonas sp. was the main dechlorinating bacterium, but its removal ability is limited. The removal of trichloroethylene in such a barrier mainly depends on reduction by the zero-valent iron and biodegradation. The results show that the prepared ceramsite is stable and effective in removing trichloroethylene from water. It is a promising in-situ remediation material for groundwater.

Sustained release of persulfate from inert inorganic materials for groundwater remediation

Groundwater has often been plagued by persistent contaminants such as dense nonaqueous phase liquids (DNAPLs). There is a need for sustained release technologies to ensure long-term treatment in these flow systems. Innovative methods involving sustained release of a selected reagent, persulfate, through pellets made from inorganic materials such as zeolite, diatomite, and silica flour are reported through a proof-of-concept study. Efficacy of the method relies on the preservation of the reagent without decreasing the treatment potential that would otherwise occur with organic matrices. Several methods and different matrix materials for pellet fabrication are described for sustained release of persulfate as a model reagent. Some pellets (diameter: 13 mm; thickness: 2.5–2.7 mm; mass: 0.5 g) show persulfate release of >25 h. Larger pellets are expected to provide longer release times. Different pellet types and fabrication methods offer a range of ease of pellet construction, as well as reagent release times for sustained release. Trichloroethylene (TCE), a DNAPL, was selected as the model contaminant for testing this sustained release approach. Treatment of 15 mg L−1 (ppm) TCE solutions showed 99% degradation, and the pellets remained intact afterwards. The current work demonstrates the potential feasibility of sustained persulfate release from inert matrices for groundwater treatment.

Simulated solar light-driven photocatalytic degradation of trichloroethylene in water using BiOBr promoted by sulfite addition

BackgroundPhotodegradation of trichloroethylene (TCE) in aqueous solution under simulated solar light irradiation was studied under different experimental conditions to determine the reaction mechanism and kinetics that control TCE degradation using bismuth oxybromide (BiOBr) in the presence of sulfite. Photocatalysts were synthesized to be more responsive to visible light under simulated solar light and particular attention was focused on the reactive specie formed by reaction of the sulfite on the surface of BiOBr under simulated sunlight.ResultDegradation rate of TCE was greatly enhanced by the presence of sulfite, and the enhancement increased with sulfite dose to a maximum that was retained at higher sulfite doses. Degradation rate of TCE was also affected by other factors, such as initial TCE concentration, BiOBr dose, and solution pH. In addition, the cycling performance of BiOBr was examined, and the amount of TCE degraded was almost constant over increasing cycle numbers when initial sulfite concentration was high enough to maintain a suitable sulfite concentration throughout the experiment. When TCE was degraded by BiOBr in the presence of sulfite under simulated sunlight irradiation, the major by-product measured was the non-hazardous chloride ion, and dechlorination efficiency was about 58%.ConclusionThis study extended the use of a potential effective photocatalyst (BiOBr) to a semi-volatile organic contaminant (TCE), not limited to mainly focus on organic dyes, and evaluated the use of sulfite as a hole scavenger in order to enhance the degradation of TCE without needing to manipulate the structure of BiOBr. The active species being responsible for TCE degradation in BiOBr/TCE/sulfite system under simulated solar light was the sulfite radical (SO3·−), and the photocatalytic activity of BiOBr did not decrease over a number of treatment cycles when SIV dose was sufficient.

Efficient novel amphiphilic double shells layer coupled with nanoscale zero-valent composite for the degradation of trichloroethylene

An efficient novel amphiphilic material composed of core-double shells nanocomposite (CDSN) with nanoscale zero-valent iron (NZVI) as the core and PS100-b-PAA16 as inner shell and chitosan as outmost shell has been synthesized successfully. Its application to remove the trichloroethylene (TCE) in stimulated TCE solution with 7.3 ± 0.3 mg/L dissolved oxygen was investigated. The results showed that CDSN after exposure to air for a month could still remove 92.6% of TCE as compared to 61.5% removal rate of NZVI in 360 min (the gram ratio of material: TCE equals to 10:1), exhibiting the great oxidation resistance performance. Specifically, dynamic research of the total removal divided into adsorption by shell layer and degradation by reducibility of NZVI at a predetermined interval was engaged to understand the complete mass transfer process of TCE. The results revealed that CDSN adsorbed 1.5 to 2 folds time TCE as compared to NZVI in the same initial pH = 8.5 aqueous solution. Importantly, CDSN could sustain fixed reactivity to remove about 94.8% of TCE from the start to end. NZVI exhibited greater removal capacity in first 180 min, but later it lost the reducibility and finial removal rate was 89%. The selective adsorption to protonated CDSN was strengthened to increase the removal of TCE at pH 3.5 while NZVI had a worse removal in pH 3.5 performance than pH 8.5.

Biotoxicity of Water-Soluble UV Photodegradation Products for 10 Typical Gaseous VOCs.

Ultraviolet (UV) photodegradation is increasingly applied to control volatile organic compounds (VOCs) due to its degradation capabilities for recalcitrant compounds. However, sometimes the UV photodegradation products are also toxic and can affect human health. Here, 10 VOCs at 150~200 ppm in air were treated using a laboratory-scale UV reactor with 185/254 nm irradiation, and the biotoxicity of their off-gas was studied by investigating their off-gas absorption solutions. The CO2 increase and VOC decrease were 39~128 ppm and 0~42 ppm, respectively, indicating that the VOCs and their products were mineralized in off-gas absorption solutions. The total organic carbon (TOC) of the absorption solutions are 4~20 mg∙L−1. Luminescent bacteria and Daphnia magna were used to detect the acute toxicity, and an umu assay was used to determine the genotoxic potential. Trichloroethylene showed a highest toxicity to luminescent bacteria, while chlorobenzene had the lowest toxicity. Water-soluble UV photodegradation products for styrene are very toxic to Daphnia magna. In the umu assay, the genotoxicities of off-gas absorption solutions of trichloroethylene, methylbenzene, ethyl acetate, butyl alcohol, and styrene were 51.26, 77.80, 86.89, 97.20, and 273.62 mg (4-NQO)·L−1 respectively. In addition, the analysis of the genotoxicity/TOC and intermediates products indicated that the off-gas absorption solutions of styrene, trichloroethylene, and butyl alcohol contain many highly toxic substances.

Effect of trichloroethylene enhancement on deposition rate of low-temperature silicon oxide films by silicone oil and ozone

A low-temperature silcon oxide film was deposited at 160 to 220 °C using an atmospheric pressure CVD system with silicone oil vapor and ozone gases. It was found that the deposition rate is markedly increased by adding trichloroethylene (TCE) vapor, which is generated by bubbling TCE solution with N2 gas flow. The increase is more than 3 times that observed without TCE, and any contamination due to TCE is hardly observed in the deposited Si oxide films from Fourier transform infrared spectra.

Test of aerobic TCE degradation by willows (Salix viminalis) and willows inoculated with TCE-cometabolizing strains of Burkholderia cepacia.

Trichloroethylene (TCE) is a widespread soil and groundwater pollutant and clean-up is often problematic and expensive. Phytoremediation may be a cost-effective solution at some sites. This study investigates TCE degradation by willows (S. viminalis) and willows inoculated with three strains of B. cepacia (301C, PR1-31 and VM1330-pTOM), using chloride formation as an indicator of dehalogenation. Willows were grown in non-sterile, hydroponic conditions for 3weeks in chloride-free nutrient solution spiked with TCE. TCE was added weekly due to rapid loss by volatilization. Chloride and TCE in solution were measured every 2-3days and chloride and metabolite concentrations in plants were measured at test termination. Based on transpiration, no tree toxicity of TCE exposure was observed. However, trees grown in chloride-free solution showed severely inhibited transpiration. No or very little chloride was formed during the test, and levels of chloride in TCE-exposed trees were not elevated. Chloride concentrations in chloride containing TCE-free nutrient solution doubled within 23days, indicating active exclusion of chloride by root cell membranes. Only traces of TCE-metabolites were detected in plant tissue. We conclude that TCE is not, or to a limited extent (less than 3%), aerobically degraded by the willow trees. The three strains of B. cepacia did not enhance TCE mineralization. Future successful application of rhizo- and phytodegradation of TCE requires measures to be taken to improve the degradation rates.

Hydrogen Isotope Exchange of Chlorinated Ethylenes in Aqueous Solution: Possibly a Termolecular Liquid Phase Reaction.

This work reports an experimental study of the hydrogen/deuterium exchange in the basic aqueous solutions of trichloroethylene, trans-1,2-dichloroethylene, and cis-1,2-dichloroethylene using (1)H NMR as a monitoring method. 1,1-Dichlorethylene was also investigated but found not to exchange hydrogen isotopes with water. The kinetics of isotope exchange features two different pathways, the first is first order with respect to hydroxide ion, whereas the second is second order. The first pathway is interpreted as a straightforward bimolecular reaction between chloroethylene and hydroxide ion, which leads to the deprotonation of chloroethylene. The second pathway involves a transition state with the association of one molecule of the chloroethylene and two hydroxide ions. It is shown that the second pathway could involve the formation of a precursor complex composed of one chloroethylene molecule and one hydroxide ion, but a direct termolecular elementary reaction is also feasible, which is shown by deriving a theoretical highest limit for the rate constants of termolecular reactions in solution.

Inferential monitoring of chlorinated solvents through Raman spectroscopic observation of the vibrational modes of water

Recent improvements in diode laser, fiber optic, and data acquisition technology have rejuvenated interest in field applications of Raman spectroscopy in a wide range of settings. One such application involves the observation of chlorinated solvents to facilitate the practice of "monitored natural attenuation." In this context, this manuscript focuses on means to improve the sensitivity of in-situ Raman analysis of chlorinated solvents. In particular, the work explores the performance limits of a Time-Resolved Raman Spectroscopy (TRRS) system employed to observe chlorinated solvents in aqueous samples via laboratory tests conducted on both liquid standards of trichloroethylene (TCE) and simulated biodegraded field samples. Quantitative assessment of TCE in solution is carried out through both direct observation of TCE Raman functional groups (381cm−1 (δ skeletal), 840cm−1 (νCCl) and 1242cm−1 (δCH)) and indirect observation of the broad OH stretching (2700–3800cm−1) Raman modes of water. Results from tests on simple solutions show that the TRRS system can detect TCE at aqueous concentrations as low as 70ppm by directly monitoring the 381cm−1 TCE line, whereas observation of the OH stretching line of water (3393cm−1) provides an indirect indication of TCE presence with nearly a 9× improvement in detection level. This unique and counterintuitive mechanism to detect the presence of chlorinated compounds in solution takes advantage of the influence of chlorine on the vibrational modes of water. This influence, which is believed to be attributed to the formation of hydrogen bonds and their resultant interactions with the solvation shell, may serve as a more sensitive and robust indication of the presence of aggregate chlorinated solvent contamination in aqueous systems. Tests performed on simulated biodegraded field samples demonstrate that the indirect detection mechanism is apparent even in complex samples representative of typical field conditions.

Permeation of organic contaminants through PVC pipes

Permeation of benzene, toluene, and trichloroethylene (TCE) through polyvinyl chloride (PVC) pipes from vapor and aqueous phases was investigated using pipe‐bottle tests, gravimetric sorption tests, and microscopic visualization tests. Vapors of the three compounds at saturated vapor pressures were found to permeate 1‐in. PVC pipes within 30 days; saturated aqueous solutions of benzene and TCE also permeated 1‐in. PVC pipes but at breakthrough times ranging from 60 to 240 days, depending on mixing conditions. For PVC pipes exposed to organic vapors that were in equilibrium with ∤ 40% v/v benzene or toluene in National Institute of Standards and Technology reference fuel and to water containing ∤ 60% of the aqueous solubility of benzene and toluene, insignificant sorption and no moving front were detected. Test results suggest that PVC pipe materials are an effective barrier against the permeation of benzene, toluene, ethylbenzene, and xylenes in either gasoline vapors or gasoline‐contaminated groundwater at typical contaminated sites.

TCE reduction modeling in soil column: Effect of zero-valent iron, ferrous iron, and iron-reducing bacteria

A model was developed to simulate the reduction of trichloroethylene (TCE) by permeable reactive barriers (PRBs). The model based on an axial transport model with chemical reaction terms was operated for a TCE solution, incorporating dispersion, convection, and reaction along the column flow-path and time. Reaction terms included TCE reduction by zero-valent iron (ZVI) or ferrous iron produced from ferric iron by iron-reducing bacteria (IRB). ZVI was oxidized by TCE to ferric iron which has no ability to reduce TCE. IRB reduced ferric iron to ferrous iron by transferring electrons from organic carbon sources such as lactate or glucose. Ferrous iron, thus produced, constantly reduced TCE although it had a relatively low reducing power compared to ZVI. The TCE concentration at the mid-port of the ZVI column was lower than one-tenth of the influent concentration until 200 h, but reached a 99% breakthrough at 1,390 h. The TCE reduction efficiency by the ZVI column was not recovered after the breakthrough. On the other hand, the life of ferrous iron column was prolonged in the presence of IRB. The TCE reduction efficiency was maintained at over 60% with 10,000 mg-IRB/L–pore volume of IRB. These results indicate that the application of IRB would be economical for a long-term operation of iron-based PRBs.

A study on radiation technological degradation of organic chloride wastewater—Exemplified by TCE and PCE

This paper describes the potential of using gamma radiation technology to degrade trichloroethylene (TCE) and perchloroethylene (PCE) wastewater. The experimental method is divided into two parts: (1) using the γ-ray to irradiate the TCE and PCE solution, the dose-rate is 10 Gy/minute, the irradiation dosage is 0–2.5 kGy and (2) self-making the UV irradiation system, the tube specification is 254 nm and 6 W, and turning on 8 tubes at the same time to make the irradiation. The efficiency of degradation ratio for γ-ray is better than UV in the range of 0.1–250 ppm; for example, as for the concentration of 0.1 ppm, when TCE is degraded to D 90 and T 90, the γ-ray only needed 46.7 Gy and took about 4.67 minutes, but UV needed to take about 28.1 minutes. The dose-concentration equations of TCE and PCE are: TCE: y=44.58+8.832 x, R 2=0.999; and PCE: y=81.33+12.81 x, R 2=0.997. We verified that the radiation technology is able to effectively degrade the organic chlorine wastewater without yielding the secondary pollution, and the TCE and PCE that degraded by using γ-ray will be reached US-EPA and Taiwan Effluent Standard (5 ppb).

Efficacy of controlled-release KMnO 4 (CRP) for controlling dissolved TCE plume in groundwater: A large flow-tank study

A well-based, reactive barrier system using controlled-release potassium permanganate (CRP system) was recently developed as a long-term treatment option for dilute plumes of chlorinated solvents in groundwater. In this study, we performed large-scale ( L × W × D = 8 m × 4 m × 2 m) flow-tank experiments to examine remedial efficacy of the CRP system. A total of 110 CRP rods (OD × L = 5 cm × 150 cm) were used to construct a well-based CRP system (L × W × D = 3 m × 4 m × 1.5 m) comprising three discrete barriers installed at 1-m interval downstream. Natural sands having oxidant demand of 3.7 g MnO 4 - kg −1 for 500 mg L −1 MnO 4 - were used as porous media. After MnO 4 - concentrations were somewhat stabilized (0.5–6.0 mg L −1), trichloroethylene (TCE) plume was flowed through the flow-tank for 53 d by supplying 1.19 m 3 d −1 of TCE solution. Mean initial TCE concentrations were 87 μg L −1 for first 20 d and 172 μg L −1 for the next 33 d. During TCE treatment, flow velocity (0.60 m d −1), pH (7.0–8.2), and concentrations of dissolved metals ([Al] = 0.7 mg L −1, [Fe] = 0.01 mg L −1) showed little variations. The MnO 2(s) contents in the sandy media measured after the TCE treatment ranged from 21 to 26 mg kg −1, slightly increased from mean baseline value of 17 mg kg −1. Strengths of the TCE plume considerably diminished by the CRP system. For the 87 μg L −1 plume, TCE concentrations decreased by 38% (53), 67% (29), and 74% (23 μg L −1) after 1st, 2nd, and 3rd barriers, respectively. For the 172 μg L −1 plume, TCE concentrations decreased by 27% (125), 46% (93), and 65% (61 μg L −1) after 1st, 2nd, and 3rd barriers, respectively. Incomplete destruction of TCE plume was attributed to the lack of lateral dispersion in the unpumped well-based barrier system. Development of delivery systems that can facilitate lateral spreading and mixing of permanganate with contaminant plume is warranted.

Dechlorination of Trichloroethylene (TCE) by Zero-Valent Iron

Dechlorination of TCE was done using zero-valent iron in two forms: powder and shavings. A simulated TCE solution of initial concentration 5 ppm was mixed with iron powder, finer than 100 mesh, in 120-mL serum bottles. The pH of the solution was varied at 5, 7 and 9; the amount of iron powder was at 10, 12.5 and 15 mg per mL of TCE solution; and the water used was distilled de-ionized water. On the other hand, 50 grams of iron shavings were used as materials packed in a glass column passed with simulated TCE solutions. Two thicknesses of the shavings were used (1 mm and 1.5 mm). The iron shavings were subjected to different preparations: pretreated with 0.1 M NaCl solution and untreated; and the water used was de-oxygenated, de-ionized distilled water. Samples taken at different intervals were analyzed for TCE and chloride ion concentrations. Results showed a decrease in the concentration of TCE, accompanied by the formation and increase in chloride ion concentration over time, thus confirming the dechlorination of TCE. Degradation was possible when the pH of the solution was 7 and below, while better dechlorination was observed with the thinnest iron shavings possible and with the said shavings subjected to pretreatment with the NaCl solution.

Radiation-initiated dechlorination of organochlorine ecotoxicants

The yields of chloride ions produced by the action of γ-radiation on aqueous, aqueous alcohol, and alcohol solutions of trichloroethylene, hexachlorocyclohexane, sodium 2,4-dichlorophenoxyacetate, pentachlorophenol, hexachlorobenzene, and Sovtol-10 (polychlorinated biphenyl) were measured. The effect of alkali and oxygen on the dehalogenation of these compounds was examined. Dechlorination in an aqueous medium is effected by eaq and OH radicals, as well as by hydrolysis of the radicals produced from the compounds in question. In an alkaline alcohol, chain dehalogenation processes involving electron transfer from the alcohol radical anion to a chlorinated organic molecule develop. It was found that Sovtol-10 is almost completely (by 99.7%) dechlorinated in a 1% solution at a dose of ≤20 kGy.

Persulfate oxidation of trichloroethylene with and without iron activation in porous media

In situ chemical oxidation with persulfate anion ( S 2 O 8 2 - ) is a viable technique for remediation of groundwater contaminants such as trichloroethylene (TCE). An accelerated reaction using S 2 O 8 2 - to destroy TCE can be achieved via chemical activation with ferrous ion to generate sulfate radicals ( SO 4 - · ) ( E ° = 2.6 V ) . The column study presented here simulates persulfate oxidation of TCE in porous media (glass beads and a sandy soil). Initial experiments were conducted to investigate persulfate transport in the absence of TCE in the column. The persulfate flushing exhibited a longer residence time and revealed a moderate persulfate interaction with soils. In TCE treatment experiments, the results indicate that the water or persulfate solution would push dissolved TCE from the column. Therefore, the effluent TCE concentration gradually increased to a maximum when about one pore volume was replaced with the flushing solution in the column. The presence of Fe 2+ concentration within the column caused a quick drop in effluent TCE concentration and more TCE degradation was observed. When a TCE solution was flushing through the soil column, breakthrough of TCE concentration in the effluent was relatively slow. In contrast, when the soil column was flushed with a mixed solution of persulfate and TCE, persulfate appeared to preferentially oxidize soil oxidizable matter rather than TCE during transport. Hence, persulfate oxidation of soil organics may possibly reduce the interaction between TCE and soil (e.g., adsorption) and facilitate the transport of TCE through soil columns resulting in faster breakthrough.

Assembly structure control of single wall carbon nanotubes with liquid phase naphthalene adsorption

Naphthalene was adsorbed on single wall carbon nanotubes (SWNT) from trichloroethylene solution. The adsorbed state of naphthalene on dry SWNT samples was studied with X-ray photoelectron spectroscopy and Raman spectroscopy. Adsorption of naphthalene molecules on SWNTs in trichloroethylene provide a uniform coating of external surface of individual SWNTs. Also, a technique of the liquid phase adsorption of naphthalene succeeded to control the assembly structure of the SWNTs, leading to an explicit adsorption hysteresis in the nitrogen adsorption isotherm at 77 K.

Influence of pH on persulfate oxidation of TCE at ambient temperatures

In situ chemical oxidation (ISCO) is a technology used for groundwater remediation. This laboratory study investigated the use of the oxidant sodium persulfate for the chemical oxidation of trichloroethylene (TCE) at near ambient temperatures (10, 20 and 30 °C) to determine the influence of pH (pH = 4, 7 and 9) on the reaction rate (i.e., pseudo-first-order rate constants) over the range of temperatures utilized. TCE solutions (60 mg l −1; 0.46 mM) were prepared in phosphate buffered RO water and a fixed persulfate/TCE molar ratio of 50/1 was employed in all tests. Half-lives of TCE degradation at 10, 20 and 30 °C (pH 7) were 115.5, 35.0 and 5.5 h, respectively. Maximum TCE degradation occurred at pH 7. Lowering system pH resulted in a greater decrease in TCE degradation rates than increasing system pH. Radical scavenging tests used to identify predominant radical species suggested that the sulfate radical ( SO 4 - ) predominates under acidic conditions and the hydroxyl radical ( OH) predominates under basic conditions. In a side by side comparison of TCE degradation in a groundwater vs. unbuffered RO water it was demonstrated that when the system pH is buffered to near neutral pH conditions due to the presence of natural occurring groundwater constituents that the TCE degradation rate is higher than in unbuffered RO water where the system pH dropped from 5.9 to 2.8. The results of this study suggest that in a field application of ISCO, pH should be monitored and adjusted to near neutral if necessary.