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PDF US Patent No 7,431,849-B1: Encapsulated Reactant and Process

PDF US Patent No 8,210,773-B2: Process for In Situ Treatment of Soil and Groundwater

PDF US Patent No 8,366,350-B2: Process for In Situ Treatment of Soil and Groundwater

Related Publications

Abstract
The development of slow-release chemical oxidants for sub-surface remediation is a relatively new technology. Our objective was to develop slow-release persulfate-paraffin candles to treat BTEX-contaminated groundwater. Laboratory-scale candles were prepared by heating and mixing Na2S2O8 with paraffin in a 2.25 to 1 ratio (w/w), and then pouring the heated mixture into circular molds that were 2.38 cm long and either 0.71 or 1.27 cm in diameter. Activator candles were prepared with FeSO4 or zerovalent iron (ZVI) and wax. By treating benzoic acid and BTEX compounds with slow-release persulfate and ZVI candles, we observed rapid transformation of all contaminants. By using 14C-labeled benzoic acid and benzene, we also confirmed mineralization (conversion to CO2) upon exposure to the candles. As the candles aged and were repeatedly exposed to fresh solutions, contaminant transformation rates slowed and removal rates became more linear (zero-order); this change in transformation kinetics mimicked the observed dissolution rates of the candles. By stacking persulfate and ZVI candles on top of each other in a saturated sand tank (14 × 14 × 2.5 cm) and spatially sampling around the candles with time, the dissolution patterns of the candles and zone of influence were determined. Results showed that as the candles dissolved and persulfate and iron diffused out into the sand matrix, benzoic acid or benzene concentrations (Co = 1 mM) decreased by >90% within 7 d. These results support the use of slow-release persulfate and ZVI candles as a means of treating BTEX compounds in contaminated groundwater.

Abstract
Past disposal of industrial solvents into unregulated landfills is a significant source of groundwater contamination. In 2009, we began investigating a former unregulated landfill with known trichloroethene (TCE) contamination. Our objective was to pinpoint the location of the plume and treat the TCE using in situ chemical oxidation (ISCO). We accomplished this by using electrical resistivity imaging (ERI) to survey the landfill and map the subsurface lithology. We then used the ERI survey maps to guide direct push groundwater sampling. A TCE plume (100–600 μg L−1) was identified in a low permeable silty-clay aquifer (Kh = 0.5 m d−1) that was within 6 m of ground surface. To treat the TCE, we manufactured slow-release potassium permanganate candles (SRPCs) that were 91.4 cm long and either 5.1 cm or 7.6 cm in dia. For comparison, we inserted equal masses of SRPCs (7.6-cm versus 5.1-cm dia) into the low permeable aquifer in staggered rows that intersected the TCE plume. The 5.1-cm dia candles were inserted using direct push rods while the 7.6-cm SRPCs were placed in 10 permanent wells. Pneumatic circulators that emitted small air bubbles were placed below the 7.6-cm SRPCs in the second year. Results 15 months after installation showed significant TCE reductions in the 7.6-cm candle treatment zone (67–85%) and between 10% and 66% decrease in wells impacted by the direct push candles. These results support using slow-release permanganate candles as a means of treating chlorinated solvents in low permeable aquifers.

Abstract
A controlled-release technique using potassium permanganate (KMnO4) has been recently developed as a long-term and semi-passive remediation scheme for dilute groundwater plumes of chlorinated solvents such as trichloroethylene (TCE) and perchloroethylene. Batch experiments were performed to evaluate TCE removal efficiencies of a low concentration of permanganate (MnO4 −) solution and to estimate the optimum dose of permanganate required to remove low levels of TCE from groundwater plumes without leaving intermediate organic forms. Experimental results indicated that when the molar ratio of [MnO4 −]0/[TCE]0 was about 10, 95% of the TCE in the plume was removed within less than 90 min, and about 90% of the chloride in the organic forms was converted into inorganic ions, while the TCE removal rates and the chloride conversion rates were considerably lower when the [TCE]0/[MnO4 −]0 values were lower. These data suggested that the [MnO4 −]0 and the [MnO4 −]0/[TCE]0 values would have strong effects on the efficiency and completeness of TCE oxidation. Further detailed investigations of the effect of [MnO4 −]0 and [MnO4 −]0/[TCE]0 values on the removal efficiencies and completeness of the TCE oxidation are warranted for successful application of the controlled-release KMnO4 technique in practice.

Abstract

Abstract
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 kg−1 for 500 mg L−1 were used as porous media. After 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 m3 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 MnO2(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.

Abstract
Release and spreading of permanganate ( ) in the well-based controlled-release potassium permanganate (KMnO4) barrier system (CRP system) was investigated by conducting column release tests, model simulations, soil oxidant demand (SOD) analyses, and pilot-scale flow-tank experiments. A large flow tank (L × W × D = 8 m × 4 m × 3 m) was constructed. Pilot-scale CRP pellets (OD × L = 0.05 m × 1.5 m; n = 110) were manufactured by mixing ∼198 kg of KMnO4 powders with paraffin wax and silica sands in cylindrical moulds. The CRP system (L × W × D = 3 m × 4 m × 1.5 m) comprising 110 delivery wells in three discrete barriers was constructed in the flow tank. Natural sands (organic carbon content = 0.18%; SOD = 3.7–11 g kg−1) were used as porous media. Column release tests and model simulations indicated that the CRP system could continuously release over several years, with slowly decreasing release rates of 2.5 kg d−1 (day one), 109 g d−1 (day 100), 58 g d−1 (year one), 22 g d−1 (year five), and 12 g d−1 (year 10). Mean concentrations within the CRP system ranged from 0.5 to 6 mg l−1 during the 42 days of testing period. The continuously releasing was gradually removed by SOD limiting the length of zone in the porous media. These data suggested that the CRP system could create persistent and confined oxidation zone in the subsurface. Through development of advanced tools for describing agent transport and facilitating lateral agent spreading, the CRP system could provide new approach for long-term in situ treatment of contaminant plumes in groundwater.

Abstract
A well-based reactive barrier system using controlled-release KMnO4 has been recently developed as a long-term in situ treatment option for plumes of dense and non-aqueous phase liquids in groundwater. In order to take advantage of the merits of controlled release systems (CRS) in environmental remediation, the release behavior needs to be optimized for the hydrologic and environmental conditions of target treatment zone. Where release systems are expected to be operated over long times, like for the reactive barriers, it may only be practical to describe the long-term behavior numerically.
We developed a numerical model capable of describing release characteristics associated with variable forms and structures of long-term CRS. Sensitivity analyses and illustrative simulations showed that the release kinetics and durations would be constrained by changes in agent solubility, bulk diffusion coefficients, or structures of the release devices. The generality of the numerical model was demonstrated through simulations for CRS with monolithic and double-layered matrices. The generalized model was then used for actual design and analyses of an encapsulated-matrix CRS, which can yield constant release kinetics for several years. A well-based reactive barrier system (4.05 × 103 m3) using the encapsulated-matrix CRS can release ∼1.65 kg of active agent (here ) daily over the next 6.6 yr, creating prolonged reaction zone in the subsurface. The generalized model-based, target-specific approach using the long-term CRS could provide practical tool for improving the efficacy of advanced in situ remediation schemes such as in situ chemical oxidation, bioremediation, or in situ redox manipulation. Development of techniques for adjusting the bulk diffusion coefficients of the release matrices and facilitating the lateral spreading of the released agent is warranted.

Abstract
In situ chemical oxidation (ISCO) using potassium permanganate (KMnO4) has been widely used as a practical approach for remediation of groundwater contaminated by chlorinated solvents like trichloroethylene. The most common applications are active flushing schemes, which target the destruction of some contaminant source by injecting concentrated permanganate ( solution into the subsurface over a short period of time. Despite many promising results, KMnO4 flushing is often frustrated by inefficiency associated with pore plugging by MnO2 and bypassing. Opportunities exist for the development of new ISCO systems based on KMnO4.
The new scheme described in this paper uses controlled–release KMnO4 (CRP) as an active component in the well-based reactive barrier system. This scheme operates to control spreading of a dissolved contaminant plume. Prototype CRP was manufactured by dispersing fine KMnO4 granules in liquid crystal polymer resin matrix. Scanning electron microscope data verified the formation of micro-scale (ID = 20–200 μm) secondary capillary permeability through which is released by a reaction-diffusion process. Column and numerical simulation data indicated that the CRP could deliver in a controlled manner for several years without replenishment. A proof-of-concept flow-tank experiment and model simulations suggested that the CRP scheme could potentially be developed as a practical approach for in situ remediation of contaminated aquifers. This scheme may be suitable for remediation of sites where accessibility is limited or some low-concentration contaminant plume is extensive. Development of delivery systems that can facilitate lateral spreading and mixing of with the contaminant plume is warranted.

Abstract
Potassium permanganate was encapsulated in various polymers to create microcapsules with slow-release properties. Batch tests were conducted to evaluate the rates at which the microcapsules release permanganate. The release histories of 18 different polymer formulations varied strongly, but average initial release rate was 2.70g KMnO 4 released g KMnO 4 initial −1 d −1 , and the release rate typically decreased with time. The total duration of release ranged from 3to80days , with an average of 27days . In other batch tests trichloroethene (TCE) was degraded to below detectable amounts by the microcapsules. The degradation rate for TCE was three to four times faster during the initial reaction period than predicted based on permanganate release rates. There appear to be several promising environmental applications for this method of creating a slow-release oxidant.

  • Kang et al. “Production and Characterization of Encapsulated Potassium Permanganate for Sustained Release as an in Situ Oxidant” Industrial and Engineering Chemistry Research 43 (2004), 5187-5193

Abstract
Potassium permanganate (KMnO4) has been widely applied as an oxidant for in situ remediation of contaminated groundwater and soil. This study describes the creation and characterization of encapsulated KMnO4 particles, the purpose of which is to serve as a material that can be specifically targeted and delivered to a contaminant source zone for optimal oxidative destruction of the contaminant. Multinuclear particulate KMnO4 with a mean equivalent spherical diameter of 15 (± 8.6) μm was incorporated into a paraffin wax matrix and then pulverized, resulting in completely or partially encapsulated particles with a mean equivalent spherical diameter of 874 (± 377) μm. Paraffin wax is biodegradable and insoluble in water, and yet is very soluble in most hydrophobic contaminants, including chlorinated solvents such as perchloroethylene (PCE). Thus, KMnO4 is released very slowly into water from the encapsulating matrix, but the oxidant is rapidly released into PCE. The release kinetics of KMnO4 from the encapsulated particles into water were characterized by an initial rapid release (<10 min), followed by significantly sustained release in later stages. The estimated times for 90% release of the oxidant were 1.6 months, 19.3 years, and 472 years for paraffin wax to KMnO4 mass ratios of 1:1, 2:1 and 5:1, respectively. The encapsulated KMnO4 particles preferentially accumulated at the PCE-water interface, and the KMnO4 was rapidly released into pure phase PCE ( 3 min) as the paraffin wax completely dissolved.

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