Clifford J. Bruell

Thermally Activated Persulfate Oxidation of Trichloroethylene (TCE) and 1,1,1-Trichloroethane (TCA) in Aqueous Systems and Soil Slurries

Under thermally activated conditions (i.e., temperature of 40∼99°C), there is considerable evidence that the persulfate anion () can be converted to a powerful oxidant known as the sulfate free radical (), which could be used in situ to destroy groundwater contaminants. In this laboratory study only limited trichloroethylene (TCE) degradation and no 1,1,1-trichloroethane (TCA) degradation was observed at 20°C. However, TCE and TCA were readily oxidized at 40°, 50°, and 60°C as a result of thermally activated persulfate oxidation. Experiments revealed that the pseudo-first-order reaction rate constants describing contaminant degradation increased with temperature. In aqueous systems activation energies for the TCE and TCA oxidation at an oxidant/contaminant molar ratio of 10/1 were determined to be 97.74±3.04 KJ/mole and 163.86±1.38 KJ/mole at pH 6 and an ionic strength of 0.1, respectively. A significant degradation of TCE and TCA occurs at 40° and 50°C, respectively, within less than 6 h. Aqueous system experiments revealed that oxidation reactions proceed more rapidly at increased persulfate/contaminant molar ratios. Soil slurry tests were conducted using medium to fine sands containing a range of fraction of organic carbon (foc) levels. Soil slurries were prepared at a 1/5 soil/water (mass ratio). In soil slurries the foc exhibited significant competition for sulfate free radicals produced. Based on these results, it was anticipated that higher temperatures, longer treatment times, and higher dosages of persulfate are required for the effective treatment of target contaminants in soil systems vs. aqueous systems.

Iron (II) Activated Persulfate Oxidation of MGP Contaminated Soil

The persulfate anion (S2O8 2−) is a strong oxidant with a redox potential of 2.01 V. However, when mixed with iron (II), it is capable of forming the sulfate radical (SO4 −.) that has an even higher redox potential (E o = 2.6 V). In these studies the sulfate radical was investigated to determine if it was a feasible oxidant for the destruction of BTEX and PAH compounds found in MGP contaminated soil. The sulfate radical was generated by either the sequential addition of iron (II) solutions or by a single addition of a citric acid chelated iron (II) solution. The sequentially added iron destroyed 86% of the total BTEX concentration and 56% of the total PAH concentration in the soil. The citric acid chelated iron destroyed 95% of the total BTEX concentration and 85% of the total PAH concentration. A second dose of persulfate and citric acid chelated iron (II) resulted in the destruction of 99% of the total BTEX concentration and 92% of the total PAH concentration. In both the sequential and chelated iron studies the lower molecular weight BTEX compounds were oxidized to a greater extent than the higher molecular weight BTEX compounds, whereas the oxidation of PAH compounds showed no preference to molecular weight.

Use of Fenton's reagent for the degradation of TCE in aqueous systems and soil slurries.

Fentons reaction is comprised of hydrogen peroxide (H2O2) catalyzed by iron, producing the hydroxyl radical (·OH), a strong oxidant. ·OH in turn may react with H2O2 and iron and is capable of destroying a wide range of organic contaminants. In this laboratory study, Fentons reaction was observed in aqueous and soil slurry systems using trichloroethylene (TCE) as the target contaminant, with the goal of maximizing TCE degradation while minimizing H2O2 degradation. Fentons reaction triggers a complex matrix of reactions involving ·OH, H2O2, iron, TCE, and soil organics. In soil slurries with a high fraction of organic carbon (fOC), iron tends to sorb to soil organics and/or particles. In aqueous systems the optimal ratio of H2O2:Fe2+:TCE to degrade TCE in a timely fashion, minimize costs, and minimize H2O2 degradation is 300 mg/L: 25 mg/L: 60 mg/L (19:1:1 molar ratio), while soil slurries with a fOC up to approximately 1% and a soil:water ratio of 1:5 (weight ratio) require about ten times the amount of H2O2, the optimal ratio being 3000 mg/L: 5 mg/L: 60 mg/L (190:0.2:1 molar ratio). TCE degradation rates were observed to decrease in soil slurries with higher fOC because of competition by soil organic matter, which appears to act as a sink for ·OH. H2O2 degradation rates tended to increase in soil slurries with higher fOC, most likely due to increased demand for ·OH by soil organics, increased available iron and other oxidation processes.

INDUCED SOIL VENTING FOR RECOVERY / RESTORATION OF GASOLINE HYDROCARBONS IN THE VADOSE ZONE

Abstract Induced soil venting can be a rapid, efficient method for the removal of insular and pellicular gasoline trapped in soils following a spill or leak. Evaporation rates of over 50 gasoline hydrocarbon components were measured in laboratory soil column experiments. The effects of soil density, moisture content, particle size, and induced air flow rate were determined. Residual soil saturation by gasoline and soil permeability to air and water were evaluated over the range of soil conditions. Gasoline recovery from soils by soil venting exceeded 99 per cent in all experiments as determined by GC, GC/MS and bulk weight analyses. Sequential volatilization of gasoline components was related to compound vapor pressure and mole fraction variations in the solvent phase with respect to time. Equilibrium and diffusion limitations of the soil venting process are analyzed and discussed. Applications of the column study to in situ soil venting in the field are discussed.

Effects of emulsion viscosity during surfactant‐enhanced soil flushing in porous media

Surfactants can potentially improve the efficiency of pump‐and‐treat technology for remediation of aquifers contaminated by nonaqueous phase liquids (NAPLs). However, the formation of emulsions during the removal process can Increase the viscosity in the system. This can result in pore clogging and reduction of flow, which inhibits the contaminant removal process. Formation of viscous emulsions has been identified in previous research as one of the probable causes for in situ field test failures using surfactant‐enhanced soil‐flushing technology. However, the effects of in situ emulsification and viscosity increases have not been quantified previously. The purpose of this article is to investigate effects of in situ emulsification on the remediation process. Laboratory column studies examined the mobilization of m‐xylene from porous media using a 1% alcohol ethoxylate surfactant solution (Witconol® SN90). Effects of in situ emulsification were determined. Glass columns (1.1 cm i.d. × 30 cm) were packed wi...

Laboratory evaluation of a biodegradable surfactant for In Situ soil flushing

Laboratory studies were performed to examine the removal of NAPL m‐xylene from porous media using a biodegradable 5% sodium lauroy/sarcosinate surfactant flushing solution (Hamposyl L‐30, Hampshire Chemical Corp., Nashua, NH). Vertical glass columns were packed with 0.6‐mm glass beads or washed sand and contaminated with m‐xylene. Columns were drained by gravity so that the media initially contained three phases: air, water, and m‐xylene. Removal of m‐xylene was primarily by enhanced solubilization. Recovery of 95% of residual m‐xylene from washed sand was obtained with an average of 43.2 pore volumes of surfactant solution, as opposed to an estimated 477 pore volumes required when flushing with water alone. Addition of surfactants caused decreases in interfacial tensions and therefore column dewatering that resulted in decreased flow rates through the unsaturated media. Effluent samples were acidified to induce phase separation via formation of water insoluble sarcosine acid, which was observed as a whit...

American petroleum institute in situ air sparging database

An evaluation of data detailing in situ air sparging (IAS) systems at 59 sites has been assembled into an American Petroleum Institute in situ Air Sparging Database (API‐IAS Database). The database was developed to provide site managers insights concerning the state‐of‐the‐art of IAS system design, operation, and evaluation. The IAS radius of influence (ROI) is often evaluated based on changes in a number of physical, chemical, or biological monitoring parameters. Measurements of groundwater dissolved oxygen levels was the technique used most often to determine the ROI. Other parameters such as pressure changes in the vadose and saturated zones, groundwater mounding, air bubbling in wells and tracer gases were also used to aid in the determination of the IAS ROI. A review of 37 pilot studies revealed that the IAS ROI is generally between 10 to 26 ft. IAS technology is generally being applied in sandy soils. The application of IAS technology was deemed infeasible at seven sites where soils contained high l...