Reaction of Nonaqueous Phase TCE with Permanganate

Oct 28, 2005 - Diana B. Loomer , Tom A. Al , Vernon J. Banks , Beth L. Parker and K. Ulrich Mayer. Environmental Science & Technology 2010 44 (15), 59...
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Environ. Sci. Technol. 2005, 39, 9303-9308

Reaction of Nonaqueous Phase TCE with Permanganate KYEHEE KIM* AND MIRAT D. GUROL† Department of Civil and Environmental Engineering, San Diego State University, San Diego, California 92182

Oxidative treatment of trichloroethylene (TCE) in the form of dense nonaqueous-phase liquid (DNAPL) by potassium permanganate (KMnO4) was investigated in a series of batch tests. The study focused on understanding the fundamental mechanisms of oxidative removal of DNAPL TCE by permanganate oxidation. Dissolution experiment for DNAPL TCE has been performed as a control experiment in the absence of KMnO4. DNAPL TCE dissolved into the aqueous phase until it reached the saturation concentration of 1200 mg/L (9.16 × 10-3 M) at 20 °C. The rate of dissolution of DNAPL TCE was proportional to the volume of the DNAPL. In the presence of KMnO4, the experimental results showed that the amount of TCE oxidized during the reaction was increased continuously as [MnO4-] decreased even though the rate decreased as [MnO4-] decreased. It was apparent that more DNAPL TCE was removed with a faster rate for higher initial permanganate concentration. At high permanganate concentration, the aqueous concentration of TCE was kept low and practically constant by the chemical reaction between aqueous TCE and MnO4-. However, as MnO4- was consumed in the system, the aqueous concentration started to increase until it reached solubility. From experimental observation, 1.561.78 mol of MnO4- was consumed per mole of TCE oxidized. Furthermore, 2.85-2.98 mol of Cl- was released to the solution per mole of TCE oxidized. Since the complete mineralization of TCE requires 2.0 mol of MnO4- and releases 3 mol of Cl- per mol of TCE oxidized, the observed stoichiometric factors indicated incomplete mineralization of TCE, but nearly complete dechlorination. Enhancement factor due to chemical reaction was quantified experimentally. The enhancement factor was shown to be a function of the molar ratio of MnO4- to TCE in the system, and hence varied during the reaction period.

Introduction Chlorinated solvents are major pollutants of groundwater and the largest group of compounds on the U.S. Environmental Protection Agency’s priority pollutant list. In addition to dissolved phase, many chlorinated solvents do exist in groundwater as dense nonaqueous-phase liquid (DNAPL). Pump-and-treat processes have not been quite successful in remediating sites with DNAPL present (1). In-situ application of various oxidants, such as potassium permanganate (KMnO4), Fenton’s reagent (2), and ozone (3), have showed varying successes. In-situ oxidation with permanganate of * Corresponding author address: PBS&J, 11125 Caminito Arcada, San Diego, CA 92131. Phone: 858-578-8056. Fax: 760-633-3978. E-mail: [email protected]. † E-mail: [email protected]. 10.1021/es050830i CCC: $30.25 Published on Web 10/28/2005

 2005 American Chemical Society

chlorinated ethylenes has been a relatively common practice because of the fast reaction of MnO4- with carbon-carbon double bonds and because MnO4- delivery to the contaminated sites has been easier than the delivery of the alternative oxidants (4, 5). The effectiveness of permanganate to destroy chlorinated ethylenes, specially TCE, has been demonstrated in many laboratory (6-8) and field studies (6, 9). The majority of these studies focused on the dissolved form of TCE in aqueous phase (7, 8, 10, 11) and showed that the complete redox reaction between TCE and permanganate can be described as

Cl2CdCHCl + 2MnO4- f

2CO2 + 2MnO2(s) + 3Cl- + H+ (1)

The few studies involving KMnO4 with TCE as a DNAPL addressed overall DNAPL TCE reduction through monitoring of MnO4- reduction and/or chloride (Cl-) production, without an attempt to elucidate individual DNAPL TCE degradation steps (6, 12-15). The exception was a recent rather systematic work by Urynowicz (16), who studied the degradation of DNAPL TCE in phosphate-buffered deionized water using reaction/ extraction vessels and showed that the DNAPL TCE degradation increased in the presence of MnO4-. The experimental results showed increased interface mass flux of TCE at high permanganate dosage during the initial stage of test. The present study has focused on the understanding of fundamental mechanisms involved during the interaction of DNAPL TCE with KMnO4. Specifically, we addressed in a completely mixed batch system (i) the dissolution of DNAPL TCE in the absence of KMnO4, (ii) degradation of DNAPL TCE by KMnO4, and (iii) evaluation of the enhancement in the degradation rate of DNAPL TCE by chemical reaction.

Experimental Approach Materials. TCE (C2HCl3, 99.9%) was obtained from Fisher Scientific. Milli-Q water (Millipore) was used throughout the studies. KMnO4 (99+%) was obtained from Aldrich Chemical. The stock solution of 10-20 g/L was prepared by dissolving KMnO4 crystals in Milli-Q water. The reducing agent, sodium thiosulfate (Na2S2O3, 99%), was obtained from Aldrich Chemical and was prepared as a stock solution (6 g/L) for quenching chemical reactions. A hexane of pesticide grade from Fisher Scientific was used as a liquid-liquid extraction solvent for the analysis of TCE. Procedure. Degradation of DNAPL TCE by KMnO4 was studied by a batch technique. Conical vials (5.0 mL graduated V-vial from Wheaton) were used as reaction vessels to minimize the displacement of DNAPL TCE under mixing conditions. Each reaction vessel was filled with 1 mL of unbuffered deionized (DI) water, and 10 or 100 µL of DNAPL TCE was carefully placed in the conical bottom of the vial. A predetermined volume of permanganate stock solution prepared from KMnO4 crystal (DI water for control) was added to the vessel, and then the vessel was filled with DI water leaving no void space. The vessels were sealed immediately and placed on a bench shaker with constant mixing of 120 rpm with which the aqueous phase was mixed thoroughly without disrupting the DNAPL TCE at the bottom of the vessel. At the end of the prescribed reaction time, a portion of the bulk aqueous phase was sampled and analyzed for aqueousphase concentrations of MnO4, [MnO4-]AQ, chloride, [Cl-], and TCE, [TCE]AQ. The total TCE concentration that includes VOL. 39, NO. 23, 2005 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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TABLE 1. Experimental Conditions for DNAPL TCE Degradation in the Absence and Presence of MnO4- a VDNAPL (µL)

mass of DNAPL (mol)

[MnO4-] (M)

mass of MnO4- (mol)

analyzed species

10 10 10 100 100 100

1.1 × 10-4 1.1 × 10-4 1.1 × 10-4 1.1 × 10-3 1.1 × 10-3 1.1 × 10-3

0 0.02 0.04 0 0.02 0.04

0 1.0 × 10-4 2.0 × 10-4 0 1.0 × 10-4 2.0 × 10-4

[TCE]AQ, [Cl][TCE]AQ, [TCE]HEX, [MnO4-]AQ, [Cl][TCE]AQ, [TCE]HEX, [MnO4-]AQ, [Cl][TCE]AQ, [Cl][TCE]AQ, [TCE]HEX, [MnO4-]AQ, [Cl][TCE]AQ, [TCE]HEX, [MnO4-]AQ, [Cl]-

a

Each experiment was performed in triplicate.

DNAPL phase plus [TCE]AQ was experimentally determined by hexane extraction method followed by GC analysis. It was assumed that the reduction of sample volume resulting from [TCE]AQ measurement would not affect the total aqueous volume (2-5% of the aqueous phase was used for [TCE]AQ measurement) or the total mass of TCE. Chemical Analysis. A portion of the aqueous sample was diluted and filtered by Acrodisc 0.1 µm super membrane filter (Pall Corp.) to remove any MnOx prior to the analysis of MnO4-. [MnO4-]AQ was measured by a spectrophotometer at a wavelength of 526 nm. The method detection level (MDL) for MnO4- was determined to be 0.003 mM by using the following equation (17):

quantity. MDISS is the total amount of TCE dissolved into the aqueous phase at time t, MDNAPL is the mass of the nonaqueous-phase TCE remaining at time t, and MAQ is the mass of TCE present in the aqueous phase at time t. MDISS and MAQ are equal in the absence of an oxidant. MDISS or MAQ can be estimated at a given time by measuring the aqueous TCE concentration, [TCE]AQ, and the volume of aqueous phase, VAQ.

MDL ) t(c) × SD × C/M

MDNAPL ) MIN - ([TCE]AQVAQ)

(2)

where t(c) is students’ t-value appropriate for a 99% confidence level and a standard deviation estimate with n - 1 degree of freedom, and t is 3.14 for seven replicates. M and SD stand for the mean and the standard deviation for the replicate analysis, and C is the lowest standard solution concentration of MnO4-, 0.01 mM. A 0.2 mL aliquot of reducing agent stock solution was added to the diluted aqueous samples (including control) prior to Cl- analysis in order to quench the reaction in the samples. A Dionex DX-500 ion chromatograph system (AS11 analytical column, AG-11 guard column, 20 mM NaOH isocratic eluent mode) with electron capture detector (ECD) was used for Cl- analysis. The aqueous sample was treated with hexane for extraction of aqueous TCE into hexane. The extract was diluted and analyzed chromatographically by a GC. The remaining reaction vessel contents were transferred to an extraction vial that contained an equal volume of hexane, and total TCE, [TCE]HEX (DNAPL plus aqueous phase), was extracted into the hexane phase, diluted, and quantified by GC analysis. The GC system was a Hewlett-Packard HP 6890 series (DB-5 column, 0.32 mm × 30 m × 0.25 µm) with ECD. The temperature setup was 35 °C for 5 min, 10 °C/ min to 70 °C, and 20 °C/min to 200 °C with running time of 15 min. Helium and nitrogen gases were used as a carrier and a makeup gas, respectively. The method detection level (MDL) for TCE by the hexane extraction method was determined to be 2.05 ppb (µg/L) by using eq 2 with the lowest standard [TCE]AQ of 0.1 µM or 13.15 µg/L. Mass Balance Relationships for the Experimental System. For a batch experimental system, the following mass balance relationships can be induced, assuming that the dissolution of DNAPL TCE into the aqueous phase is the only process affecting the change in nonaqueous- and aqueous-phase TCE in the absence of MnO4-:

MIN ) MDISS + MDNAPL

(3)

MDISS ) MAQ

(4)

where MIN is the initial mass of nonaqueous-phase TCE introduced at the beginning of the experiment and is a known 9304

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MAQ ) MDISS ) [TCE]AQVAQ

(5)

MDNAPL can be quantified as follows on the basis of the relationship presented in eq 3.

(6)

The mass balance equations in the presence of MnO4can be written on the basis of the assumptions that (1) DNAPL TCE dissolves into the aqueous phase, (2) the chemical reaction between MnO4- and TCE occurs in the aqueous phase following dissolution, and (3) these are the only two major processes affecting the mass balance relationships. So, the mass balance for TCE can be expressed as

MIN ) MDISS + MDNAPL ) MTOTAL + MOX

(7)

MTOTAL ) MAQ + MDNAPL

(8)

where MOX is the mass of TCE removed by chemical oxidation at time t and MTOTAL is the total mass of TCE present in aqueous and nonaqueous phases in the system at time t. By measuring [TCE]AQ and [TCE]HEX, MAQ and MTOTAL can be quantified as presented in eqs 5 and 9, respectively.

MTOTAL ) [TCE]HEXVHEX

(9)

Thus, MOX and MDNAPL can be calculated as

MOX ) MIN - MTOTAL ) MIN - ([TCE]HEXVHEX) (10) MDNAPL ) MTOTAL - MAQ ) MTOTAL - ([TCE]AQVAQ) (11)

Results and Discussion Table 1 lists the experimental conditions of the DNAPL TCE degradation study. The amount of TCE DNAPL and MnO4are given in µL and mol, and in M and mol, respectively. For 10 µL TCE, initial MnO4- applied was 0, and about one and two times the amount of the total TCE. For 100 µL TCE, the initial MnO4- applied was 0, and about 10% and 20% the amount of the total TCE. Dissolution Experiments in the Absence of MnO4. The dissolution of DNAPL TCE was monitored by measuring [TCE]AQ as a function of time (Figure 1). The DNAPL TCE dissolved faster from 100 µL of DNAPL compared to 10 µL of DNAPL. Within about 20 h [TCE]AQ reached 1200 mg/L (9.16 × 10-3 M) for 100 µL of DNAPL. For VDNAPL ) 10 µL, it took about six times longer to reach the same equilibrium

FIGURE 1. TCE accumulation in the aqueous-phase by dissolution of DNAPL TCE in the absence of MnO4-.

FIGURE 3. Change in MOX with time (where, for example, 1.5E-04 represents 1.5 × 10-4). [KMnO4]0 ) 0, 0.02, and 0.04 M.

FIGURE 2. Change in [MnO4-] with time. [KMnO4]0 ) 0, 0.02, and 0.04 M. concentration. From this result, it is clear that a larger volume of DNAPL TCE or larger interfacial area of the DNAPL resulted in faster mass transfer to the aqueous phase otherwise under the same experimental conditions. The aqueous concentration of chloride ion, [Cl-], was also monitored to check the possible reductive dechlorination of TCE by thiosulfate, the reducing solution. Microbial reductive dechlorination of TCE by thiosulfate is known to occur by sulfate reducing bacteria; however, the increase of chloride ion concentration due to the addition of thiosulfate was not detected throughout this study. DNAPL TCE Reduction in the Presence of MnO4-. The results in terms of the change in [MnO4-] with time are presented in Figure 2 for 10 and 100 µL of DNAPL and different initial concentrations of MnO4-. The [MnO4-] was continuously decreased and reached under MDL during the reaction. In the presence of more DNAPL TCE (VDNAPL ) 100 µL), the rate of MnO4- consumption was faster. At t ) 20 and 10 h, permanganate was almost consumed for 10 and 100 µL of DNAPL, respectively. Any further TCE removal by MnO4oxidation beyond these times would not be expected. Figure 3 shows the change in MOX with time for [MnO4-]0 ) 0, 0.02, and 0.04 M for (a) VDNAPL ) 10 µL and (b) VDNAPL

) 100 µL. MOX was defined as the amount of TCE removed from the system at time, t, as presented by eq 10. TCE started to get removed immediately after the introduction of MnO4-, but the reaction practically stopped at about 20 h for 10 µL of DNAPL TCE and at 10 h for 100 µL of DNAPL TCE, when MnO4- was completely used up in the systems (see Figure 2). As expected, more TCE was removed at higher [MnO4-]0 levels, indicating that the oxidative reaction of TCE by MnO4- was the main mechanism of removal of TCE in this system. When the [MnO4-]0 was increased from 0.02 to 0.04 M, the MOX at the end of experiment (t ) 24 h) increased 1.85 and 1.6 times for VDNAPL ) 10 µL (0.11 × 10-3 mol) and 100 µL (1.1 × 10-3 mol), respectively. Continuous removal of TCE was observed even after MnO4- disappeared from the system. This may be observed because there may be mechanisms other than permanganate oxidation to remove TCE in the presence of MnO4-, such as manganese dioxide (MnO2) oxidation of TCE or adsorption of TCE onto MnO2 precipitates. To check the stoichiometric relation between TCE and MnO4-, these variables were plotted against each other in Figure 4 in terms of moles of TCE oxidized and MnO4consumed. The best statistical fit revealed a stoichiometric factor of about 1.56-1.78 MnO4- consumed per mole of TCE oxidized for both 10 and 100 µL DNAPL volumes. This is short of the theoretical amount of 2.0 for complete oxidation, indicating a two-step reaction as proposed by Yang and Schwartz (11), where the first step involves the reaction of 1 mol of MnO4- with 1 mol of TCE, leading to the conversion of TCE to carboxylic acids. The second step involves the oxidation of carboxylic acids to CO2 through the consumption of a second mole of MnO4-. Hence, the observed stoichiometric factor of 1.6-1.8 indicates that some portion of the carboxylic acids has not yet been mineralized to CO2. Figure 5 shows the change in MDNAPL with time at [MnO4-]0 ) 0, 0.02, and 0.04 M for (a) VDNAPL ) 10 µL and (b) VDNAPL ) 100 µL. The decrease in MDNAPL in the absence of MnO4is due to the dissolution of DNAPL TCE into the aqueous phase. VOL. 39, NO. 23, 2005 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 4. Stoichiometric relation between TCE oxidized and MnO4- consumed (where, for example, 2.50E-04 represents 2.50 × 10-4).

FIGURE 6. Change in MAQ with time (where, for example, 2.0E-05 represents 2.0 × 10-5). [KMnO4]0 ) 0, 0.02, and 0.04 M.

FIGURE 5. Change in MDNAPL with time (where, for example, 1.5E-04 represents 1.5 × 10-4). [KMnO4]0 ) 0, 0.02, and 0.04 M. In the presence of MnO4-, the mass of DNAPL change was much higher than the dissolution alone observed in the absence of MnO4-, because DNAPL TCE was affected by dissolution and oxidation by MnO4- simultaneously. Furthermore, more DNAPL TCE was removed at higher [MnO4-]0 values. Beyond 20 h for VDNAPL ) 10 µL and 10 h for VDNAPL ) 100 µL when MnO4- was consumed completely in the systems, MDNAPL reduction would be mainly affected by the dissolution or other TCE removal reactions than permanganate oxidation. 9306

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The change in the mass of TCE in the aqueous phase, MAQ, with time is presented in Figure 6 in the absence and presence of MnO4-, where the initial TCE concentration is zero. In the absence of MnO4-, the TCE concentration gradually increased to reach the aqueous solubility of 1200 mg/L (or MS ) 4.56 × 10-5 mol of TCE dissolved in 5 mL of water, where MS is the mass-converted solubility) within 24 h for 100 µL of DNAPL TCE. For 10 µL of DNAPL TCE, MAQ could not reach the MS value within 24 h. In the presence of MnO4-, MAQ could not increase to the levels observed in the absence of MnO4- because of removal of TCE from the aqueous phase by oxidation. Over the 24 h period, MAQ in the presence of 0.04 M KMnO4 remained close to zero for 10 µL of DNAPL TCE. For other conditions, MAQ was much lower in the presence of MnO4- than in the absence of MnO4- and

FIGURE 7. Change in the mass of Cl- with time (where, for example, 4.0E-04 represents 4.0 × 10-4). [KMnO4]0 ) 0, 0.02, and 0.04 M. started to increase only after MnO4- was depleted. This observation indicates that the dissolution rate of DNAPL TCE controls the overall reaction rate in the presence of MnO4-. Yet, the oxidation cannot be considered a “fast” reaction under the experimental conditions, since the aqueous TCE was always above the detection limit of TCE. For 100 µL of DNAPL TCE, MAQ continued to remain low even after MnO4was depleted for an additional 10 h, indicating that (1) aqueous TCE might continue to be removed by mechanisms other than direct oxidation by MnO4- or (2) MnO2 precipitates might delay the dissolution of nonaqueous-phase TCE into the aqueous phase. The reaction product chloride ion, Cl-, accumulated in the aqueous solution, is presented in Figure 7 as units of

mole. In the absence of MnO4-, no Cl- was detectable. Any production of chloride ion in the presence of thiosulfate was not detected in this study. In the presence of MnO4-, the quantity of Cl- increased, with the rate about three times higher than the rate of the MOX (Figure 3). The stoichiometric relation between TCE and Cl- was explored by plotting the mole of TCE oxidized versus the mole of Cl- produced in the reaction. Figure 8 shows the stoichiometric factors as 2.98 and 2.85 for the 10 and 100 µL of TCE DNAPL, respectively. Both of these factors are slightly lower than the theoretically expected value of 3.0. Again, the results indicate that TCE has not been completely mineralized, and a very small portion of the reaction intermediates in the form of carboxylic acids (0.65%) are still chlorinated even at the point of complete consumption of MnO4-. The larger discrepancy between the observed and the theoretical values of the stoichiometric factor for 100 µL of TCE DNAPL, where the total MnO4consumed is only 10-20% of the initial TCE, would be quite understandable on the basis of the scenario of incomplete mineralization. On the other hand, even after MnO4- was completely depleted in solutions, the production of Cl- has continued for both 10 and 100 µL of DNAPLs. Furthermore, after MnO4- was depleted in the solution, the color of the test solutions changed from dark brown, and finally to clear with formation of the blackish precipitate, MnO2. During this period, we speculate that the colloidal MnO2 might continue to serve as a weak oxidant to slowly mineralize TCE. Experimentally Obtained Enhancement Factor. The enhancement factor, E*, is defined here as the ratio of the amount of DNAPL TCE transferred in a given time into aqueous solution in the presence of MnO4- to the amount which would be transferred in the absence of MnO4-. Therefore, experimentally determined E* can be written as

E* )

(∆MDNAPL)w

(12)

(∆MDNAPL)w/o

where (∆MDNAPL)w and (∆MDNAPL)w/o are the changes of MDNAPL within the time interval of ∆t, in the presence and absence of the oxidant, respectively. The enhancement factor was quantified on the basis of the experimental measurements and was plotted in Figure 9 for 10 and 100 µL of DNAPL. As presented in Figure 9, TCE oxidation in the aqueous phase significantly enhanced the overall TCE degradation.

FIGURE 8. Stoichiometric relation between TCE oxidized and Cl- accumulated (where, for example, 4.00E-04 represents 4.00 × 10-4). VOL. 39, NO. 23, 2005 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 9. Experimentally determined enhancement due to chemical oxidation. The E* was strongly dependent on [MnO4-], as would be expected. Initially at high concentration of MnO4-, the E* values were as high as 30 for 10 µL and 8 for 100 µL of DNAPL. As MnO4- was depleted, the E* values declined rapidly, though they were still higher than 1.0 at all times. For similar MnO4values, E* was about 4 times higher for 10 µL of DNAPL than 100 µL of DNAPL, indicating a direct proportionality between E* and the molar ratio of MnO4- to TCE. As a result, it can be concluded that permanganate oxidation enhances the DNAPL TCE removal significantly by increasing the rate of dissolution of TCE from DNAPL to water.

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(4) Lee, D. G. In Hydrocarbon Oxidation Using Transition Metal Compounds. Oxidation, Vol. 1; Augustine, R. T., Ed.; Marcel Dekker Inc.: New York, 1969; pp 2-46. (5) Lee, D. G. The Oxidation of Organic Compounds by Permanganate Ion and Hexa-Valent Chromium; Open Court Publishing Co.: La Salle, 1980; 20pp. (6) Schnarr, M.; Truax, C.; Farquhar, G.; Hood, E.; Gonullu, T.; Stickney, B. Laboratory and Controlled Field Experiments Using Potassium Permanganate To Remediate Trichloroethylene and Perchloroethylene DNAPLs in Porous Media. J. Contam. Hydrol. 1998, 29, 205-224. (7) Huang, K. C.; Hoag, G. E.; Chheda, P.; Woody, B. A.; Dobbs, G. M. Kinetic Study of Oxidation of Trichloroethylene by Potassium Permanganate. Environ. Eng. Sci. 1999, 16 (4), 265-274. (8) Yang, Y. E.; Schwartz, F. W. Oxidative Degradation and Kinetics of Chlorinated Ethylenes by Potassium Permanganate. J. Contam. Hydrol. 1999, 37, 343-365. (9) Siegrist R. L.; Urynowicz, M. A.; Crimi, M. L.; Lowe, K. S. Genesis and Effects of Particles Produced during In Situ Chemical Oxidation Using Permanganate. J. Environ. Eng. 2002, 128 (11), 1068-1079. (10) Hood, E. D.; Thomson, N. R.; Grossi, D.; Farquhar, G. J. Experimental Determination of the Kinetic Rate Law for the Oxidation of Perchloroethylene by Potassium Permanganate. Chemosphere 2000, 40, 1383-1388. (11) Yang, Y. E.; Schwartz, F. W. Kinetics and Mechanisms for TCE Oxidation by Permanganate. Environ. Sci. Technol. 2000, 34, 2535-2541. (12) Moes, M. J.; Peabody, C. E.; Siegrist, R.; Urynowicz, M. In Treating Dense Nonaqueous-Phase Liquids (DNAPLs); Wickramanayake, G. B., Gavaskar, A. R., Chen, A. S. C., Eds.; Battelle Press: Columbus, OH, 2000; pp 117-124. (13) Mott-Smith, E.; Leonard, W. C.; Lewis, R.; Clayton, W. S.; Ramirez, J.; Brown, R. In Treating Dense Nonaqueous-Phase Liquids (DNAPLs): Wickramanayake, G. B., Gavaskar, A. R., Chen, A. S. C., Eds.; Battelle Press: Columbus, OH, 2000; pp 125-134. (14) Schroth, M. H.; Oostrom, M.; Wietsma, T. W.; Istok, J. D. In-Situ Oxidation of Trichloroethylene by Permanganate: Effects on Porous Medium Hydraulic Properties. J. Contam. Hydrol. 2001, 50, 79-98. (15) Hunkeler, D.; Aravena, R.; Parker, B. L.; Cherry, J. A.; Diao, X. Monitoring Oxidation of Chlorinated Ethenes by Permanganate in Groundwater Using Stable Isotopes: Laboratory and Field Studies. Environ. Sci. Technol. 2003, 37, 798-804. (16) Urynowicz, M. A. Reaction Kinetics and Mass Transfer during in Situ Oxidation of Dissolved and DNAPL Trichloroethylene with Permanganate. Ph.D. dissertation, Colorado School of Mines, Golden, CO, 2000. (17) Wirt, K.; Laikhtman, M.; Rohrer, J.; Jackson, P. E. Low-Level Perchlorate Analysis in Drinking Water and Groundwater by Ion Chromatography. Am. Environ. Lab. 1998, 10 (3), 4-5. (18) Kim, K. Degradation of Nonaqueous Phase TCE in the Presence of Permanganate. Ph.D. disssertation, University of California, San Diego, San Diego State University, San Diego, CA, 2004.

Received for review May 2, 2005. Revised manuscript received September 14, 2005. Accepted September 15, 2005. ES050830I