Enhanced attenuation: Its place in the remediation of chlorinated solvents

The development and regulatory acceptance of monitored natural attenuation (MNA) as a remedial strategy has forever changed the field of environmental cleanup. MNA is continuing to develop but it is challenged by a lack of a clear definition for the appropriate application of the MNA strategy. This challenge has resulted in the lack of a significant record of restoration and site closure. Environmental professionals face challenges in providing guidance that addresses how to manage these sites when technologies, performance monitoring, and even environmental conditions are subject to further development, refinement, and/or altered perspectives. As our experience and institutional knowledge grows around the implementation of MNA, we have the opportunity to develop “second‐generation” management tools and procedures for optimizing sites utilizing MNA as a part of a comprehensive site management plan. This opportunity is the focus of the Enhanced Attenuation: Chlorinated Organics (EACO) Team of the Interstate Technology Regulatory Council (ITRC). The development of the “second‐generation” tools/procedures has included defining EA and evaluating, through the use of a national survey of state regulators, the experience with MNA and interest in EA. The results of these two efforts formed the basis for developing a framework that provides a “bridge” from active treatment to MNA. © 2007 Wiley Periodicals, Inc.     

Enhanced phytoremediation: A study of mycorrhizoremediation of heavy metal–contaminated soil

Arbuscular mycorrhizal fungi (AMF) are microscopic fungi that occur naturally in soil and form a symbiosis with plant roots. By colonizing the roots, the fungus increases plant growth by making soil essential elements like zinc and phosphorus more accessible. AMF can play a role in the phytoremediation of heavy metal–contaminated soil (mycorrhizoremediation). Two research experiments were conducted to evaluate the impact of AMF on the extraction of different heavy metals (arsenic, cadmium, lead, selenium, and zinc) in contaminated soil. A grass mixture composed of Festuca rubra, Festuca eliator, Agropyron repens, and Trifolium repens was used in the experiments, and four different types of AMF were investigated: Glomus intraradices, Glomus mosseae, Glomus etunicatum, and Gigaspora gigantea. The results of the study showed that heavy metal extraction by Glomus intraradices colonized plants was the highest of all four AMF tested and was generally higher than nonmycorrhizal plants, depending on the heavy metal concentration in soil and whether it interacted with other metals in soil. However, metal extraction by AMF colonized grasses reached a plateau after an approximately two‐month period showing no further phytoaccumulation. © 2006 Wiley Periodicals, Inc.     

Historical analysis of monitored natural attenuation: A survey of 191 chlorinated solvent sites and 45 solvent plumes

A survey of experts in the application of natural attenuation was conducted to better understand how monitored natural attenuation (MNA) is being applied at chlorinated solvent sites. Thirty‐four remediation professionals provided general information for 191 sites where MNA was evaluated, and site‐specific data for 45 chlorinated solvent plumes being remediated by MNA. Respondents indicated that MNA was precluded as a remedy at only 23 percent of all sites where evaluated as a remedial option. Leading factors excluding MNA as a remedial approach were the presence of an expanding plume and an unreasonably long estimated remediation time frame. MNA is being used as the sole remedy at about 30 percent of the sites, and 33 percent are implementing MNA in conjunction with source zone remediation. The remaining sites are implementing MNA with plume remediation (13 percent), source containment (9 percent), or some other strategy (16 percent). © 2004 Wiley Periodicals, Inc.     

Electroremediation: A study of the influence of buffering behavior in contaminated soils

This article presents the results of an experimental study conducted to evaluate the behavior of two types of andisol soils found in Tenerife, Canary Islands, Spain. The soils were evaluated in relation to their buffering capacity when confronted with acid and alkaline fronts generated during electroremediation treatment. The study was conducted using a cell, which established a continuous flow of distilled water through electrode chambers to remove H⁺ and OH^? generated during electrolysis. The results indicate that the soils had sufficient buffer capacity to support variations in pH independent of the maintenance of flow of solution in the electrode chambers. Although the mechanism of migration was not affected, the flow of water favored the movement of ions by diffusion monitoring of the electrolytic current allowed for a real‐time parameter to act as an indicator of the quantity of ions available in regions near the electrodes. © 2004 Wiley Periodicals, Inc.     

铬污染土壤处理中的铬含量及形态变化

采用FeSO_4和Na_2S作为还原剂处理铬污染紫色土壤,研究了还原过程中铬的含量及形态的变化。实验结果表明:当FeSO_4加入量为1.5%(w,下同)时,浸出Cr(Ⅵ)含量由(1 745.13±27.93)mg/kg降至(17.65±2.28)mg/kg,浸出总铬含量由(1 768.83±57.24)mg/kg降至(69.79±8.61)mg/kg,铬形态由水溶+碳酸盐结合态转变到较稳定的铁锰结合态;当Na_2S加入量为0.4%时,浸出Cr(Ⅵ)含量由(1 745.13±27.93)mg/kg降至(25.50±0.12)mg/kg,浸出总铬含量由(1 768.83±57.24)mg/kg降至(410.87±12.83)mg/kg,铬形态由水溶+碳酸盐结合态转变到铁锰结合态和有机结合态。     

Use of gold mill tailings in making bricks: a feasibility study.

Mill tailings dumps at Kolar Gold Fields, Karnataka, are creating environmental problems. One of the solutions to these problems is to use the mill tailings for some useful purpose. This study examined the possibility of making bricks from the mill tailings with some additives in laboratory experiments. Samples of the mill tailings and the additives were analysed for particle size distribution, Atterberg limits and specific gravity. The plasticity index of the mill tailings being zero, they could not be used directly for making bricks. Therefore some additives that had plasticity or binding properties were mixed with the mill tailings. Ordinary Portland cement, black cotton soils and red soils were selected as additives. Each of the additives was mixed separately with the mill tailings in different proportions by weight and a large number of bricks were prepared using metallic moulds. The bricks were termed as cement-tailings bricks or soil-tailings bricks, depending on the additives used. The cement-tailings bricks were cured for different periods and their corresponding compressive strengths were determined. The bricks with 20% of cement and 14 days of curing were found to be suitable. The soil-tailings bricks were sun-dried and then fired in a furnace at different temperatures. The quality of bricks was assessed in terms of linear shrinkage, water absorption and compressive strength. The cost analysis revealed that cement-tailings bricks would be uneconomical whereas the soil-tailings bricks would be very economical.     

皂素和柠檬酸复合淋洗土壤中的钍

采用振荡淋洗和土柱动态淋洗实验研究了皂素和柠檬酸复合对土壤中钍的淋洗性能。实验结果表明:将质量浓度为20 g/L的皂素与浓度为20 mmol/L的柠檬酸以体积比1∶10配制复合淋洗液对污染土壤中钍的去除效果最佳,淋洗3.0 h,钍去除率为84.98%;准一级动力学方程能更好地描述复合淋洗液对钍的淋洗动力学特征;动态淋洗实验中当复合淋洗液用量为1 600 mL时,钍的累积去除量为73.66 mg/kg;淋洗后土壤中钍的酸可提取态、氧化结合态和有机结合态含量分别减少了79.63%、38.13%和20.34%,残渣态含量变化不大;淋洗后土壤中钍的稳定性增加。     

Reuse of residues arising from lead batteries recycle: a feasibility study

The performance of products arising from the stabilization/solidification of slags from lead batteries recycle into a Portland cement matrix has been evaluated not only in order to get a stabilized waste to be disposed of according to the current legislation, but also to obtain a recyclable material, with both economic and environmental benefits. Under this respect a detailed characterization of raw slags has been performed and different slag-cement samples have been prepared by varying the slag content. The parameters related to the cementation process have been evaluated and a series of tests on the final waste forms have been carried out, aimed at assessing both mechanical performance and leaching behaviour. In spite of the acceptable values for flexural, compressive and tensile strength, however, the high release of lead from the solidification products seems to be a limiting factor for a reusable material. While explanations of such phenomenon are given (high alkalinity of Portland cement; early "doping" of cementitious components by lead in the amorphous state), the main conclusion of the research work is that further efforts should be addressed to the adoption of a different or a modified incorporation matrix.     

Investigation of naphtalene sulfonate compounds sorption in a soil artificially contaminated using batch and column assays

In the present work desorption tests of an artificially contaminated soil by naphatelene sulphonated compounds have been carried out by soil washing realised by water at different pH: Naphtalene-1,5-disulfonic acid (1-5 NDS), 2-naphthol-6,8 disulphonic acid (G-acid) and sodium beta-naphtalene-sulphonate (beta-salt) have been selected as more representative organic compounds present in the ex industrial site of ACNA (Cengio, SV, Italy) in which very serious contamination levels of several pollutants are present both in the soils and surface waters. Equilibrium batch tests have been carried out in order to find the best operative condition in column washing tests. The obtained results can be considered very preliminary but useful to arrange a next experimental work that will be realised on real contaminated soils.     

Biodegradation of chlorinated organic pesticides endosulfan and chlorpyrifos in soil extract broth using fungi

The present study was designed to screen 20 fungi for their potential to degrade the chlorinated organic pesticides endosulfan and chlorpyrifos. Fungi were first screened for their tolerance to various concentrations of target pesticides using soil extract agar and subsequent degradation studies were performed in soil extract broth containing 25 mg/L of the individual pesticide. Pesticide degradation was evaluated using gas chromatography. Other parameters, such as pH and mycelial weight, were also determined. Based on percent growth inhibition of test fungi and subsequent analysis of EC₅₀ values, the overall results revealed that chlorpyrifos showed significantly more growth inhibition in all tested fungi compared with endosulfan. Trametes hirsuta showed complete degradation of both α‐ and β‐endosulfan isomers and Cladosporium cladosporioides displayed maximum degradation of chlorpyrifos. All test fungi degraded endosulfan more efficiently than chlorpyrifos, except Phanerochaete chrysosporium, Trichoderma harzianum, and Trichoderma virens which showed higher degradation of chlorpyrifos than endosulfan. It was also found that all tested fungi degraded α‐endosulfan more efficiently than β‐endosulfan. Endosulfan sulfate was found to be the major degradation product with all tested fungi. Fungi which showed more endosulfan degradation also produced more endosulfan sulfate. However, less endosulfan sulfate was detected with T. hirsuta and Trametes versicolor, although they degraded endosulfan more efficiently.     

Assessing detoxification and degradation of wood preserving and petroleum wastes in contaminated soil

This study was undertaken to evaluate in-situ soil bioremediation processes, including degradation and detoxification, for two types of wood preserving wastes and two types of petroleum refining wastes at high concentrations in an unacclimated soil. The soil solid phase, water soluble fractions of the soil, and column leachates were evaluated. Two bioassays, a mutagenic potential asay (Ames assay) and an aqueous toxicity assay (Microtox^™ assay) were used to evaluate detoxification; high performance liquid chromatography was used to evaluate chemical concentration and degradation for eight polynuclear aromatic hydrocarbons (PAHs). The group of non-carcinogenic PAHs studied demonstrated greater degradation, ranging from 54–90% of mass added for the four wastes; the carcinogenic group of PAHs studied exhibited degradation ranging from 24–53% of mass added. Although no mutagenicity was observed in waste/soil mixtures after one year of treatment, Microtox^™ toxicity was observed in water soluble fractions and in leachate samples. An integration of information concerning degradation of hazardous constituents with bioassay information represents an approach for designing treatability studies and for evaluating the effectiveness of in-situ bioremediation of contaminated soil/waste systems. When combined with information from waste, site and soil characterization studies, the data generated in treatability studies may be used in predictive mathematical models to: (1) evaluate the effectiveness of use of on-site bioremediation for treatment of wastes in soil systems; (2) develop appropriate containment structures to prevent unacceptable waste transport from the treatment zone; and (3) design performance monitoring strategies.     

Remediation of DDT‐contaminated soil using optimized mixtures of surfactants and a mixing system

Soil contaminated with persistent pesticides, such as DDT, poses a serious risk to humans and to wildlife. A surfactant‐aided soil‐washing technique was studied as an alternative method for remediation of DDT‐contaminated soil. An ex situ soil washing method was investigated using nonionic and anionic surfactants due to the clayey structure of the contaminated soil. A mixture of 1 percent nonionic surfactant (Brij 35) and 1 percent anionic surfactant (SDBS) removed more than 50 percent of DDT from soil in a flow‐through system, whereas individual surfactants or other combinations of the surfactants had a lower removal efficiency. The soil‐washing technique was improved using a mixing system. The mixture of surfactants was optimized in the mixing system, and the combination of 2 percent Brij 35 and 0.1 percent SDBS was found to be optimum, removing 70 to 80 percent of DDT. Prewashing of the soil with tap water decreased the adsorption of surfactants to soil particles by 30 to 40 percent, and postwashing recovered 90 percent of the surfactants. © 2010 Wiley Periodicals, Inc.     

万山汞矿区土壤重金属污染特征及来源解析

以万山汞矿区土壤为研究对象,采用电感耦合等离子体质谱仪和原子荧光光谱仪测定土壤中的重金属含量,分别运用内梅罗综合污染指数（NPI）法和潜在生态风险指数（RI）法评价土壤重金属污染和潜在生态风险,并应用相关性分析、主成分分析和聚类分析对土壤重金属来源进行分析。结果表明：土壤Hg、Cd、As、Pb、Cu、Ni和Zn出现不同程度累积,分别达贵州省背景值的263.61、2.31、1.28、2.11、1.70、1.01和3.52倍;土壤重金属平均NPI为188.00,属于严重污染水平,Hg是主要污染因子;土壤重金属平均RI为10 655.70,属于极强潜在生态风险水平,Hg是主要潜在生态风险因子;土壤中Cu、Ni、Cr主要源于自然活动,As、Pb、Zn主要源于燃煤和交通运输污染,Cd主要源于农业污染,Hg主要源于汞冶炼污染。     

A feasibility study of thermal hydrolysis by-products as barrier layer materials in the final cover system for a landfill

Most sludge has historically been disposed of in landfills and by ocean dumping but, because of its heavy metal content, this will be totally banned in Korea starting in 2012, based on the London Dumping Convention. Therefore, treatment and disposal methods that are environmentally friendlily are urgently required. The recycling of sewage sludge is a good treatment method for solving sludge problems in an environmentally friendly way. In this study, physical and environmental tests were conducted to evaluate the feasibility of using the by-products of thermal hydrolysis of sewage sludge as barrier layer materials in the final cover systems for landfills. In addition, testing methods for freezing-thawing (KS F 2332) and wetting-drying (KS F 2330) cycles were conducted to assess the effects of cold and hot soil climates starting from pavement. These tests yielded positive results for alternative materials for the barrier layer in a final cover system for a landfill.     

Treatment of mercury‐contaminated soils with activated carbon: A laboratory,field, and modeling study

A series of laboratory batch leaching tests was conducted to evaluate the performance of different activated carbons in stabilizing mercury in soils. Based on the results of these experiments, an amendment application rate of 5 percent powdered activated carbon (PAC) was selected for in situ field application at a former industrial facility. A geochemical model was also developed to simulate the interactions between mercury and activated carbon in vadose‐zone soils. Modeling was used to (1) better understand possible mercury sequestration mechanisms and (2) predict the in situ performance of PAC. Model results indicate dissolved mercury concentrations observed in batch tests are consistent with equilibrium partitioning of mercury between dissolved organic matter, soil organic matter, and PAC. Activated carbon is predicted to reduce dissolved mercury concentrations via two mechanisms: (1) the formation of stable mercury complexes on PAC surfaces and (2) the direct adsorption of dissolved organic matter that would otherwise be available for mercury dissolution. Study results demonstrate PAC effectiveness for site soils with mercury concentrations below 200 mg/kg. © 2010 Wiley Periodicals, Inc.     

Phytoremediation: The uptake of metals and metalloids by rhodes grass grown on metal‐contaminated soil

An experiment was performed to examine the phytoremediation potential of Rhodes grass (Chloris gayana Kunth cv. ‘Pioneer’). The study sought to determine substrate tolerance, biomass production, and plant uptake of antimony (Sb), arsenic (As), cadmium (Cd), lead (Pb), silver (Ag), and zinc (Zn). The plants were grown on weight percent mixtures (5 percent, 15 percent, 25 percent, 35 percent, 50 percent) of a vertisol soil and base‐metal mine tailings (7–2,040 μg/g As, ≥ 30 μg/g Cd, 30–12,000 μg/g Pb, and 72–4,120 μg/g Zn). The 5 percent and 15 percent amendment of mine tailings increased the biomass production of Rhodes grass (from 0.1 g/plant to ≈ 3.5 g/plant) without appreciably elevating plant concentrations of the elements. Plant growth decreased by greater than 50 percent for the substrate containing greater than 25 percent tailings (3,023 μg/g Pb and 1,084 μg/g Zn). Reduced biomass production coincided with maximal Zn uptake by Rhodes grass (249.8 μg/g), indicating tailings induced phytotoxicity. The total concentrations of metals and metalloids tolerated by Rhodes grass in the plant‐growth medium indicated hypertolerance to elevated As, Pb, and Zn concentrations. Partial extraction of the plant‐growth medium determined that plant‐available Pb was ten times higher than Ag, As, Cd, and Zn availability. However, Rhodes grass accumulated low levels of Pb, in addition to As and Cd, over the experimental range, indicating low fodder toxicity risk to browsing livestock. This study concludes that if there are no invasive species issues associated with conservation land uses, Rhodes grass is well suited to metalliferous mined land revegetation and would therefore be highly effective for such programs in subtropical and tropical Australia. © 2005 Wiley Periodicals, Inc.     

Solvent extraction and soil washing treatment of contaminated soils from wood preserving sites: Bench‐scale studies

Bench‐scale solvent extraction and soil washing studies were performed on soil samples obtained from three abandoned wood preserving sites included in the National Priority List. The soil samples from these sites were contaminated with high levels of polyaromatic hydrocarbons (PAHs), pentachlorophenol (PCP), dioxins, and heavy metals. The effectiveness of the solvent extraction process was assessed using liquefied propane or dimethyl ether as solvents over a range of operating conditions. These studies have demonstrated that a two‐stage solvent extraction process using dimethyl ether as a solvent at a ratio of 1.61 per kg of soil could decrease dioxin levels in the soil by 93.0 to 98.9 percent, and PCP levels by 95.1 percent. Reduction percentages for benzo(a)pyrene (BaP) potency estimate and total detected PAHs were 82.4 and 98.6 percent, respectively. Metals concentrations were not reduced by the solvent extraction treatment. These removal levels could be significantly improved using a multistage extraction system. Commercial scale solvent extraction using liquefied gases costs about $220 per ton of contaminated soil. However, field application of this technology at the United Creosote site, Conroe, Texas, failed to perform to the level observed at bench scale due to the excessive foaming and air emission problem. Soil washing using surfactant solution and wet screening treatability studies were also performed on the soil samples in order to assess remediation strategies for sites. Although aqueous phase solubility of contaminants seemed to be the most important factor affecting removal of contaminants from soil, surfactant solutions (3 percent by weight) having nonionic surfactants with hydrophile‐lipophile balance (HLB) of about 14 (Makon‐12 and Igepal CA 720) reduced the PAH levels by an average of 71 percent, compared to no measurable change when pure deionized water was used. Large fractioza of clay and silt (<0.06mm), high le!ezielsof orgaizic contami‐ nants and hzimic acid can makesoil washing less applicable.     

Chemical Treatments of Natural Fiber for Use in Natural Fiber-Reinforced Composites: A Review

Studies on the use of natural fibers as replacement to man-made fiber in fiber-reinforced composites have increased and opened up further industrial possibilities. Natural fibers have the advantages of low density, low cost, and biodegradability. However, the main disadvantages of natural fibers in composites are the poor compatibility between fiber and matrix and the relative high moisture sorption. Therefore, chemical treatments are considered in modifying the fiber surface properties. In this paper, the different chemical modifications on natural fibers for use in natural fiber-reinforced composites are reviewed. Chemical treatments including alkali, silane, acetylation, benzoylation, acrylation, maleated coupling agents, isocyanates, permanganate and others are discussed. The chemical treatment of fiber aimed at improving the adhesion between the fiber surface and the polymer matrix may not only modify the fiber surface but also increase fiber strength. Water absorption of composites is reduced and their mechanical properties are improved.     

Case study: On-site remediation of soil and groundwater for a michigan town's water supply

In 1993 environmental consultants, working in concert with the State of Michigan, discovered groundwater contamination that threatened the drinking water supply of the town of Big Rapids. The contamination originated from leaking underground storage tanks and gasoline lines, which were removed. A pilot study indicated the contaminated area extended to 240′ x 180′ and affected soil as well as groundwater. A remediation plan was designed by and implemented by Continental Remediation Systems, Inc., a Natick, Massachusetts, firm. The remediation plan is ongoing and includes an interceptor trench to stop gasoline from flowing into the creek, as well as air sparging to vent and treat the contaminated soil. It is anticipated that the remediation project will take six months to complete. The chief advantage of on-site remediation is that it avoids the costs and liabilities associated with landfill disposal and no materials need leave the site.