Passive soil vapor extraction: A cost effectiveness study

An analysis of the cost effectiveness of passive soil vapor extraction (PSVE) is presented. PSVE, or “barometric pumping,” is an approach to the remediation of volatile organic compounds (VOCs) that seeks to harness and enhance the naturally occurring processes of wind and atmospheric pressure changes to facilitate the release of gas-phase contaminants from the subsurface. The technology background and current status are discussed, niches for the potential applicability of PSVE are identified, and a cost comparison with the conventional treatment method of active soil vapor extraction (ASVE) is examined.     

Examining the economics of remediation by fluid injection with vacuum extraction

Enhanced methods of in-situ remediation based on patented technology involving fluid injection with vacuum extraction have been used successfully at the Sand Creek Superfund Site in Commerce City, Colorado. Approximately 177,000 pounds of volatile organic compounds (VOCs) were removed from the subsurface in six months, two months ahead of schedule. Remediation goals were achieved on this thermally enhanced soil vapor extraction project by using vertical and horizontal wells interchangeably in vacuum or pressure service for vapor extraction, dual vacuum extraction, heated vapor reinjection, and air sparging. Although VOCs consisted of mixed chlorinated and petroleum hydrocarbons, the petroleum hydrocarbons, some in the form of nonaqueous phase liquids, had not been fully characterized. This article examines the evolution of the remedial design from that conceptualized in the Record of Decision (ROD) of the U.S. EPA, presents the rationale for the selection of alternative system components, and provides a cost analysis of the selected remedial technology, with comparisons to that of alternatives considered for use at Sand Creek.     

Analysis of soil vapor extraction laboratory data to obtain equilibrium constants

A method of analyzing soil vapor extraction (SVE) laboratory data using a sample of contaminated soil is presented to allow the calculation of equilibrium constants for an assumed gas/soil equilibrium expression. The constants can be determined for any compound measured in the exit gas. A Freundlich equilibrium expression was shown to represent the equilibrium in a soil contaminated with trichloroethylene (TCE) and several aromatic solvents.     

微波辐照修复氯丹污染土壤的影响因素

采用微波辐照技术修复氯丹污染土壤,以氯丹的挥发率和分解率为主要评价指标,研究了微波辐照条件对土壤修复效果的影响。实验结果表明:氯丹的挥发率随微波辐照功率的增大而增大,而氯丹的分解率则无明显变化;当活性炭与土壤质量比为9∶120时,氯丹的去除效果最好,去除率达89%;氯丹的挥发性能在前20min内随微波辐照时间的延长而增强,而氯丹的分解性能则刚好相反;当土壤含水率为15%时,氯丹的挥发率最高,为2.5%,而氯丹分解率最小,为16.8%;在酸性偏中性范围内氯丹的去除效果较差,随土壤p H的不断增大,氯丹的挥发率明显升高,且氯丹的分解率也增大。     

Preliminary comparison of alternative designs for soil remediation by bioventilation

Computer simulation provides a powerful tool for comparing alternative designs of remediation processes. The software package FLUENT copes successfully with subsurface three-dimensional flow fields, multiple and directional permeabilities, wide spatial variations in subsurface gas velocities, and the presence of surface structures. FLUENT can provide an invaluable method for comparing remediation efficiencies among competing design alternatives. This article features case studies to illustrate the benefits that simulation studies provide before and during the initiation of remedial actions using bioventing.     

Remediation of groundwater contamination through conjunctive use of landfill gas management and soil vapor extraction

The recently completed performance testing of a conjunctive-use operation has demonstrated the applicability of combined landfill gas and Volatile Organic Compound (VOC) removal with overall contaminant migration management. The extraction of landfill gas (with subsequent control of off-site gas migration) and the removal of VOCs from the landfill gas/soil air environment will minimize VOC solubilization in the underlying groundwater. This, in turn, will permit cost efficient management of contaminant migration at the site.     

热分解技术在修复多氯联苯污染土壤中的应用

针对我国土壤中PCBs的污染特点,介绍了一种修复土壤的热分解技术,并详述了该技术的工作流程、影响因素、处理效率等问题。最后对该技术的发展趋势进行了展望,并对其在推广过程中可能遇到的困难进行了分析。     

Removal of Cr(VI) from contaminated soil by electrokinetic remediation

A new process for the removal of hexavalent chromium [Cr(VI)] contaminated soil is described. The process provides for an efficient removal of anionic chemicals from contaminated soils. Chromate anions were removed from the soil to the anodic reservoir by the moving force of electromigration. In this process, the chromate anions that accumulate in the anodic reservoir are simultaneously eliminated by using a column packed adsorbent. The adsorbent (immobilized tannin) used was chemically incorporated into cellulose. Cr(VI) was found to be adsorbed to this adsorbent efficiently. In the electrokinetic process, the pH of the aqueous solution in the anodic reservoir was decreased by the electrolysis of water. In the present study, the pH of the solution in the anodic reservoir is maintained at pH 6 by the addition of an aqueous alkaline solution during the electrokinetic process. The advantage of pH control is that it promotes the release of Cr(VI) from the soil by electromigration, thus permitting the maximum adsorption of Cr(VI) on the immobilized tannin. Simultaneous collection of Cr(VI) from the anodic reservoir leads to the protection from secondary contamination with Cr(VI).     

Laboratory studies of the remediation of polycyclic aromatic hydrocarbon contaminated soil by in-vessel composting

The biodegradation of 16 polycyclic aromatic hydrocarbons (PAHs), listed as priority pollutants by the USEPA, present in a coal-tar-contaminated soil from a former manufactured gas plant site was investigated using laboratory-scale in-vessel composting reactors to determine the suitability of this approach as a bioremediation technology. Preliminary investigations were conducted over 16 weeks to determine the optimum soil composting temperature (38, 55 and 70 degrees C). Three tests were performed; firstly, soil was composted with green-waste, with a moisture content of 60%. Secondly, microbial activity was HgCl2-inhibited in the soil green-waste mixture with a moisture content of 60%, to evaluate abiotic losses, while in the third experiment only soil was incubated at the three different temperatures. PAHs and microbial populations were monitored. PAHs were lost from all treatments with 38 degrees C being the optimum temperature for both PAH removal and microbial activity. Calculated activation energy values (E(a)) for total PAHs suggested that the main loss mechanism in the soil-green waste reactors was biological, whereas in the soil reactors it was chemical. Total PAH losses in the soil-green waste composting mixtures were by pseudo-first order kinetics at 38 degrees C (k = 0.013 day(-1), R2 = 0.95), 55 degrees C (k = 0.010 day(-1), R2 = 0.76) and at 70 degrees C (k = 0.009 day(-1), R2 = 0.73).     

Destruction of PAHS from soil by using pressurized hot water extraction coupled with supercritical water oxidation

Chemical processes utilizing water both as extraction solvent and reaction medium are promising "Green Chemistry" alternatives to conventional techniques. Equipment for on-line coupled hot water extraction and supercritical water oxidation was constructed to extract polyaromatic hydrocarbons and toluene from sea sand followed by oxidation using hydrogen peroxide. The effectiveness of the technique is based on the physico-chemical properties of heated and pressurized water. Extraction efficiency increased with temperature and time; the best results were obtained at 300 degrees C with 40 min extraction time. In the oxidation stage, conversion of the PAHs increased with reaction time and oxidant concentration and the best conversion (97.0-99.9%, depending on the compound) was obtained at 425 degrees C with 43 s reaction time. Benzaldehyde and benzoic acid were the most abundant reaction intermediates in the oxidation process. In addition, phenol, p-cresol, and benzyl alcohol were found as intermediates. The intermediates originated mainly from toluene, which was present in much greater concentration than PAHs in the reaction medium.     

Demonstration of MicroBlower™ technology for sustainable soil vapor extraction: Case studies at the Savannah River Site,South Carolina

The MicroBlower Sustainable Soil Vapor Extraction System is a cost‐effective device specifically designed for remediation of organic compounds in the vadose zone. The system is applicable for remediating sites with low levels of contamination and for transitioning sites from active source technologies such as active soil vapor extraction to natural attenuation. It can also be a better choice for remediating small source zones that are often found in “tight zones” that are controlled by diffusion rate. The MicroBlower was developed by the Savannah River National Laboratory at the US Department of Energy's Savannah River Site to address residual volatile organic compound (VOC) contamination after shutdown of active soil vapor extraction systems. In addition, the system has been deployed to control recalcitrant sources that are controlled by diffusion rates. © 2012 Wiley Periodicals, Inc.     

曝气强化非离子表面活性剂洗涤法修复柴油污染土壤

采用异位修复法,利用非离子表面活性剂洗涤柴油污染土壤,并在洗涤过程中曝气强化。考察了洗涤效果的影响因素,并通过表面张力和接触角的测定探讨了洗涤机理。实验结果表明:曝气对污染土壤中柴油的洗脱有强化作用,可提高洗脱率10%~20%;3种非离子表面活性剂的洗脱效果优劣次序为聚氧乙烯月桂醚(Brij-35)曲拉通X-100(TX-100)吐温-80(Tw-80);在表面活性剂浓度为1倍临界胶束浓度、曝气量为7.5 L/min、洗涤时间为60 min、洗涤液pH为11.0的优化条件下,Brij-35对柴油的洗脱率达77.4%,污染土样的含油率从7.0%降至1.6%,接触角从24.12°降至6.65°,可基本恢复土壤的亲水性;洗涤液的表面张力随表面活性剂浓度的增加而降低,但不受洗涤液pH的影响。