In-Situ Thermal Remediation of Contaminated Soil

Recently, a method for removing contaminants from soil (several meters under the ground) has been proposed by McMillan-McGee Corp. The process can be described as follows. Over a period of several weeks, electrical energy is introduced to the contaminated soil using a multitude of finite length cylindrical electrodes. Current is forced to flow through the soil by the voltage differentials at the electrodes. Water is also pumped into the soil via the injection well and out of the ground at the extraction well. The soil is heated up by the electrical current and the contaminated liquids and vapours are produced at the extraction well. The temperature of the contaminated soil, during the process, is believed to reach the maximum value (the boiling temperature of water). Normally, the electrodes are placed around the contaminated site and the extraction well is located in the centre of the contaminated region. The distance between the electrodes is usually seven to eight meters. The distance between the extraction well and an electrode is about four meters. The diameter of the electrodes is 0.2 meter and the extraction well is 0.1 meter in diameter. The reason for using the electrical current is that “flushing” the soil using water alone is not effective for removing the contaminants. By heating up the soil and vaporizing the contaminated liquid, it is anticipated that rate of extraction will increase as long as the recondensation is not significant. A major concern, therefore, is whether recondensation will occur. Intuitively, one might speculate that liquid phase may dominate near the injection well. Moving away from the injection site towards the extraction well, due to the combined effects of lower pressure and higher temperature (from heating), phase change occurs and a mixture of vapour and liquid may co-exist. There may also be a vapour-only region, depending on the values of temperature, pressure, and other parameters. In the two-phase zone, since vapour bubbles tend to rise due to the buoyancy force, and the temperature decreases along the vertical path of the bubbles out of the heated region, it is possible that the bubbles will recondense before reaching the extraction well. As a consequence, the probability exists that part of the contaminants stay in the soil. Obviously, to predict transition between single-phase and two-phase regions and to understand the transport phenomenon in detail, a thermal capillary two-phase flow model is needed. However, to simplify the problem, here we only consider the case when two-phases co-exist in the entire region

Thermal based remediation technologies for soil and groundwater: a review

Thermal remediation technologies are fast and effective tools for the remediation of contaminated soils and sediments. Nevertheless, the high energy consumption and the effect of high temperature on the soil properties may hinder the wide applications of thermal remediation methods. This review highlights the recent studies focused on thermal remediation. Eight types of thermal remediation processes are discussed, including incineration, thermal desorption, stream enhanced extraction, electrical resistance heating, microwave heating, smoldering, vitrification, and pyrol-ysis. In addition, the combination of thermal remediation with other remediation technologies is presented. Finally, thermal remediation sustainability is evaluated in terms of energy efficiency and their impact on soil properties. The developments of the past decade show that thermal-based technologies are quite effective in terms of contaminant removal but that these technologies are associated with high energy use and costs and can has an adverse impact on soil properties. Nonetheless, it is anticipated that continued research on thermally based technologies can increase their sustainability and expand their applications. Low temperature thermal desorption is a prom-ising remediation technology in terms of land use and energy cost as it has no adverse effect on soil function after treatment and low temperature is required. Overall, selecting the sustainable remediation technology depends on the contaminant properties, soil properties and predicted risk level. © 2022 Desalination Publications. All rights reserved

Modeling Heat Propagation and Thermal Enhanced Decay in a Solar Thermal Remediation System

Low temperature solar thermal remediation is designed to accelerate ongoing biotic and abiotic treatment processes at a much lower temperature and cost than high temperature thermal remediation strategies. An array of borehole heat exchangers are used to circulate a solar-heated fluid through a closed-loop system of thermally conductive pipes. Thermal energy heats the surrounding contaminated zone through the process of thermal conduction which serves to enhance the degradation of the contaminant. A three dimensional analytical solution was previously constructed to model heat propagation from borehole heat exchangers into the surrounding subsurface. The model utilizes a system of finite line sources to describe the borehole heat exchangers while accounting for variable borehole heating rates as well as multiple borehole heaters. This user-friendly simulation model can calculate subsurface temperature change at a low computation time, and is currently being used as a guidance tool for designing and optimizing solar thermal remediation systems. The analytical design tool has been validated by comparison with field data from a solar thermal remediation test site in Colorado, and is currently being used to optimize a detailed field test on Vandenberg Space Force Base in Southern California. The analytical model is compared to high-resolution temperature data during early stages of the test, and then used to predict the longer-term performance of the solar thermal remediation system. A new feature has been added to the analytical design tool to estimate the thermal-enhanced decay of a contaminant using a modified first-order decay solution. This new capability uses temperature-dependent decay rates to project the thermal-enhanced decay of volatile organic compounds (VOC’s) over time, and is used to model VOC destruction at Vandenberg Space Force Base. With the ability to analyze the impact of increasing subsurface temperature on the duration of bioremediation projects, the decay tool offers an additional advantage in optimizing these types of remediation systems

High-Resolution Monitoring for Thermal Remediation Optimization

Abstract is in response to call for abstracts for Battelle Chlorinated Solvent Conference. The abstract discusses how we conducted high-resolution monitoring for thermal remediation optimization

Microwave-Assisted Thermal Remediation of Diesel Contaminated Soil

Leakage of petroleum products, gasoline and diesel, at gas station had become one of major soil contamination sources in Taiwan. Total number of 154 petroleum contaminated gas stations was successively ascertained since the implementation of Soil and Groundwater Remediation Act in 2002. One of the contaminated gas stations, mainly diesel polluted, was studied for the feasibility of microwave-assisted thermal remediation. The average of total petroleum hydrocarbons (TPHt) in hotspot of this site was 2,845 mg/kg exceeding regulatory limit (1,000 mg/kg). According to the groundwater condition in the site, soil samples treated by microwave radiation with and without water as saturation and vadose zones were respectively tested in laboratory. The results show that a 12-min microwave energy can heat soil with water to reach 235°C and degrade its TPHt to 934 mg/kg; additionally, a 5 min microwave energy can heat soil without water to reach 220°C and degrade its TPHt to 520 mg/kg. Both soil samples passed TPHt regulatory limit and microwave remediation with fast and effective advantages for petroleum products contaminated soil was also verified

Spent Bleaching Earth Recovery of Used Motor-Oil Refinery

Bleaching earth refers to natural or activated clay which has the capacity to adsorb colored materials and other impurities during oil purification processes. This research utilized the spent bleaching earth (SBE) in used motor oil purification process via thermal remediation (650 ˚C) and acid washing methods (1 M HCl). Then, the activated spent bleaching earth (ASBE) was characterized. The results obtained from the BET analysis show the specific surface area and pore volume of the ASBE, activated virgin bleaching earth (AVBE) and virgin bleaching earth (VBE). These parameters are 100.38 m2g-1 and 0.23 cm3g-1 for the activated spent bleaching earth, 100.82 m2g-1 and 0.22 cm3g-1 for the activated virgin bleaching earth and 83.34 m2g-1 and 0.19 cm3g-1 for the virgin bleaching earth. The BJH analysis indicates that SBE activation increases mesopores in ASBE. In addition, results obtained from the XRD and FTIR tests illustrate that activation of SBE does not affect the physical and chemical properties of montmorillonite clay. Furthermore, SEM observations indicate surface morphology improvement in ASBE. Hence, activation of earth enhances its adsorption efficiency in comparison with virgin bleaching earth