Distribution and Abiotic Degradation of Chlorinated Solvents in Heated Field Samples

The objective of this study was to evaluate the abiotic degradation of tetrachloroethylene (PCE) in contaminated soil and groundwater samples obtained from the Camelot Cleaners Superfund site, West Fargo, ND. The field samples were incubated at temperatures of 25, 55, 75, and 95 °C in sealed ampules containing aqueous, gas, and solid phases for periods of up to 75 days to simulate thermal treatment temperatures. Aqueous PCE concentrations increased with incubation temperature but remained constant over time. The degradation of dolomite to form CO2 facilitated the transfer of sorbed-phase PCE from the solid to the aqueous phase in heated ampules. While compounds associated with PCE degradation were detected in the heated ampules, these compounds were also detected in ampules with PCE-free Camelot soil and were attributed to soil diagenesis rather than PCE degradation. Trichloroethylene underwent hydrogenolysis to form cis-DCE at 95 °C, and TCE levels decreased with first-order half-lives of 157 days at 55 °C and 26 days at 95 °C. The relatively small decrease in total PCE levels after 75 days of heating at 95 °C suggests that abiotic degradation of PCE will not result in significant mass reduction during thermal treatment of the Camelot Cleaners Superfund site

Accumulation of PFOA and PFOS at the Air–Water Interface

Knowledge of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) accumulation at the air–water interface is critical to understanding the fate and transport of these substances in subsurface environments. The surface tension of aqueous solutions containing PFOA and PFOS at concentrations ranging from 0.1 to >1000 mg/L and with dissolved solids (i.e., cations and anions) commonly found in groundwater was measured using the Wilhelmy plate method. The surface tensions of solutions containing dissolved solids were lower than those for ultrapure water, indicating an increase in the surface excess of PFOA and PFOS in the presence of dissolved solids. An equation for the surface excess of PFOA and PFOS with total dissolved solids was developed by fitting the measured surface tension values, which ranged from 72.0 to 16.7 mN/m, to the Szyszkowski equation. On the basis of mass distribution calculations for a representative unsaturated, fine-grained soil, up to 78% of the PFOA and PFOS mass will accumulate at the air–water interface, with the remaining mass dissolved in water and adsorbed on the solids

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

Fate of TCE in Heated Fort Lewis Soil

This study explores the transformation of trichloroethene (TCE) caused by heating contaminated soil and groundwater samples obtained from the East Gate Disposal Yard (EGDY) located in Fort Lewis, WA. After field samples transferring into glass ampules and introducing 1.5 μmol of TCE, the sealed ampules were incubated at temperatures of 25, 50, and 95 °C for periods of up to 95.5 days. Although TCE was completely transformed into cis-1,2-dichloroethene (cis-DCE) after 42 days at 25 °C by microbial activity, this transformation was not observed at 50 or 95 °C. Chloride levels increased after 42 days at 25 °C corresponding to the mass of TCE transformed to cis-DCE, were constant at 50 °C, and increased at 95 °C yielding a TCE degradation half-life of 1.6−1.9 years. These findings indicate that indigenous microbes contribute to the partial dechlorination of TCE to cis-DCE at temperatures of less than 50 °C, whereas interphase mass transfer and physical recovery of TCE will predominate over in situ degradation processes at temperatures of greater than 50 °C during thermal treatment at the EGDY site

Abiotic Degradation of Trichloroethylene under Thermal Remediation Conditions

The degradation of trichloroethylene (TCE) to carbon dioxide (CO2) and chloride (Cl-) has been reported to occur during thermal remediation of subsurface environments. The effects of solid-phase composition and oxygen content on the chemical reactivity of TCE were evaluated in sealed ampules that were incubated at 22 and 120 °C for periods ranging from 4 to 40 days. For all treatments, no more than 15% of the initial amount of TCE was degraded, resulting in the formation of several non-chlorinated products including Cl-, CO2, carbon monoxide, glycolate, and formate. First-order rate coefficients for TCE disap pearance ranged from 1.2 to 6.2 × 10-3 day-1 at 120 °C and were not dependent upon oxygen content or the presence of Ottawa sand. However, the rate of TCE disappearance at 120 °C increased by more than 1 order-of-magnitude (1.6 to 5.3 × 10-2 day-1), corresponding to a half-life of 13−44 days in ampules containing 1% (wt) goethite and Ottawa sand. These results indicate that the rate of TCE degradation in heated, three-phase systems is relatively insensitive to oxygen content, but may increase substantially in the presence of iron bearing minerals

Enhanced Mobility of Fullerene (C₆₀) Nanoparticles in the Presence of Stabilizing Agents

Experimental and mathematical modeling studies were performed to examine the effects of stabilizing agents on the transport and retention of fullerene nanoparticles (nC₆₀) in water-saturated quartz sand. Three stabilizing systems were considered: naturally occurring compounds known to stabilize nanoparticles (Suwannee river humic acid (SRHA) and fulvic acid (SRFA)), synthetic additives used to enhance nanoparticle stability (Tween 80, a nonionic surfactant), and residual contaminants resulting from the manufacturing process (tetrahydrofuran (THF)). The results of column experiments demonstrated that the presence of THF, at concentrations up to 44.5 mg/L, did not alter nC₆₀ transport and retention behavior, whereas addition of SRHA (20 mg C/L), SRFA (20 mg C/L), or Tween 80 (1000 mg/L) to the influent nC₆₀ suspensions dramatically increased the mobility of nC₆₀, as demonstrated by coincidental nanoparticle and nonreactive tracer effluent breakthrough curves (BTCs) and minimal nC₆₀ retention. When columns were preflushed with surfactant, nC₆₀ transport was significantly enhanced compared to that in the absence of a stabilizing agent. The presence of adsorbed Tween 80 resulted in nC₆₀ BTCs characterized by a declining plateau and retention profiles that exhibited hyperexponential decay. The observed nC₆₀ transport and retention behavior was accurately captured by a mathematical model that accounted for coupled surfactant adsorption–desorption dynamics, surfactant–nanoparticle interactions, and particle attachment kinetics