原位热处理技术修复重质非水相液体污染场地研究进展

重质非水相液体(DNAPLs)是土壤及地下水中广泛存在的有机污染物,原位热处理技术是目前修复受DNAPLs污染土壤及地下水的最具潜力的技术之一。综述了国内外常用原位热处理技术的基本原理及其影响因素,介绍了相关现场应用实例,并展望了该技术未来的应用前景和发展趋势,以期为中国污染土壤及地下水的原位修复提供有益借鉴。     

超声波净化石油污染土壤实验研究

为研究超声波技术处理石油污染土壤的影响因素,选取了土壤含油量、土水比、土壤类型、超声处理时间和超声功率5个因素进行了具有交互作用的正交实验,并讨论了各因素对土壤中石油污染物清除率的影响。实验结果表明超声波对土壤中石油污染物的净化效果明显,总石油烃(TPH)的清除率在23.0%到77.3%之间,土壤类型对净化效果的影响最为显著,粘土中的TPH清除率显著低于砂土。由超声空化引起的解吸作用和真空抽滤是实验过程中土壤TPH减少的主要途径。研究结果表明超声波技术用于石油污染土壤修复是可行并且有效果的。     

典型危险废物的工程力学特性

掌握填埋废物的工程力学特性是确保危险废物填埋堆体稳定性的重要前提条件,因此,针对6种典型危险废物的工程力学特性开展了调查研究.研究结果表明,污泥类危险废物的含水率和有机质含量远高于非污泥类危险废物,而前者的比重则显著低于后者.污泥类危险废物的渗透系数相对较小,比污染土壤和飞灰炉渣混合物的渗透系数小1个数量级,比滤池填料的渗透系数小2个数量级.不同危险废物的无侧限抗压强度排序为:飞灰炉渣混合物(314.3 kPa)和滤池填料(278.9 kPa)＞污染土壤(124.9 kPa)＞杭州氧气厂污泥(68.6 kPa)、锌铬污泥(71.4 kPa)、油泥(58.4 kPa).不同危险废物的粘聚力排序为:飞灰炉渣混合物(40.8 kPa)、滤池填料(31.1 kPa)＞污染土壤(20.9 kPa)＞杭州氧气厂污泥(1.94kPa)、锌铬污泥(3.10 kPa)、油泥(1.81 kPa).此外,不同危险废物的内摩擦角差异相对较小,其变化范围在18.8°～35.0°之间.综合分析可知,飞灰炉渣混合物和滤池填料的工程力学特性较好,而污泥类危险废物的工程力学特性则较差.     

Age-dating Diesel Fuel Spills: Using the European Empirical Time-based Model in the U.S.A.

In 1993, a paper was published by Christensen and Larsen that offered a method for determining the age of diesel oil spills in soil (7Ground Water Mount.R . Fall, 142–149). It presented an empirical time-based model of the degradation of diesel fuel in soils using chemical data gathered at petroleum release sites in Denmark and the Netherlands. Now, evaluation of the validity of the application of this work to subsurface petroleum releases in other countries remains.In the U.S.A., investigations assessing date(s) of release of diesel fuel in soils, e.g. age dating of subsurface petroleum contamination, have considerable interest. Litigation-driven scientific investigations with accompanying expert testimony in a court of law are underway. The number of instances where application of the Christensen and Larsen empirical time-based model to petroleum-contaminated properties is growing in the U.S.A.This paper presents two case studies which evaluate the applicability of the Christensen and Larsen empirical time-based model to petroleum-contaminated properties in general. It illustrates the approach using gas chromatographic data from two recently-completed projects evaluating the applicability of the Christensen and Larsen model to a No. 2 fuel oil/diesel fuel surface spill in the U.S.A. Results showed that the application of the model to petroleum-contaminated soils was scientifically valid, provided its applicability was evaluated using hypothesis testing for specific changes in the characteristics of the petroleum hydrocarbon distribution in a number of soil samples collected over time at one site. The paper offers observations on the application of the Christensen and Larsen model to petroleum found in the light non-aqueous phase liquid (LNAPL) phase and groundwater.     

Plants' use of different nitrogen forms in response to crude oil contamination

In this study, we investigated Phragmites australis’ use of different forms of nitrogen (N) and associated soil N transformations in response to petroleum contamination. ¹⁵N tracer studies indicated that the total amount of inorganic and organic N assimilated by P. australis was low in petroleum-contaminated soil, while the rates of inorganic and organic N uptake on a per-unit-biomass basis were higher in petroleum-contaminated soil than those in un-contaminated soil. The percentage of organic N in total plant-assimilated N increased with petroleum concentration. In addition, high gross N immobilization and nitrification rates relative to gross N mineralization rate might reduce inorganic-N availability to the plants. Therefore, the enhanced rate of N uptake and increased importance of organic N in plant N assimilation might be of great significance to plants growing in petroleum-contaminated soils. Our results suggest that plants might regulate N capture under petroleum contamination.     

Scavenging of BHCs and DDTs from soil by thermal desorption and solvent washing

Intensive remediation of abandoned former organochlorine pesticides (OCPs) manufacturing areas is necessary because the central and surrounding soils contaminated by OCPs are harmful to crop production and food safety. Organochlorine and its residues are persistent in environments and difficult to remove from contaminated soils due to their low solubility and higher sorption to the soils. We performed a comprehensive study on the remediation of OCPs-contaminated soils using thermal desorption technique and solvent washing approaches. The tested soil was thermally treated at 225, 325, 400, and 500 °C for 10, 20, 30, 45, 60, and 90 min, respectively. In addition, we tested soil washing with several organic solvents including n-alcohols and surfactants. The optimal ratio of soil/solvent was tested, and the recycling of used ethanol was investigated. Finally, activities of polyphenol oxidase (PPO), urease (URE), alkaline phosphatase, acid phosphatase (ACP), and invertase (INV) were assayed in the treated soils. The tested soil was thermally treated at 500 °C for 30 min, and the concentration of contaminants in soil was decreased from 3,115.77 to 0.33 mg kg^?1. The thermal desorption in soil was governed by the first-order kinetics model. For the chemical washing experiment, ethanol showed a higher efficiency than any other solvent. Using a 1:20 ratio of soil/solvent, the maximum removal of OCPs was achieved within 15 min. Under this condition, approximately 87 % of OCPs was removed from the soils. More than 90 % of ethanol in the spent wash fluid could be recovered. Activities of some enzymes in soils were increased after ethanol treatment. But ALP, ACP, and INV activities were decreased and PPO and URE showed slightly higher activities following remediation by thermal treatment. Both heating temperature and time were the key factors for thermal desorption of OCPs. The n-alcohol solvent showed higher removal of OCPs from soils than surfactants. The highly efficient removal of OCPs from soil was achieved using ethanol. More than 90 % of ethanol could be recovered and be reused following distillation. This study provides a cost-effective and highly efficient way to remediate the OCPs-contaminated soils.     

A combined approach of physicochemical and biological methods for the characterization of petroleum hydrocarbon-contaminated soil

Main physicochemical and microbiological parameters of collected petroleum-contaminated soils with different degrees of contamination from DaGang oil field (southeast of Tianjin, northeast China) were comparatively analyzed in order to assess the influence of petroleum contaminants on the physicochemical and microbiological properties of soil. An integration of microcalorimetric technique with urease enzyme analysis was used with the aim to assess a general status of soil metabolism and the potential availability of nitrogen nutrient in soils stressed by petroleum-derived contaminants. The total petroleum hydrocarbon (TPH) content of contaminated soils varied from 752.3 to 29,114 mg kg^?1. Although the studied physicochemical and biological parameters showed variations dependent on TPH content, the correlation matrix showed also highly significant correlation coefficients among parameters, suggesting their utility in describing a complex matrix such as soil even in the presence of a high level of contaminants. The microcalorimetric measures gave evidence of microbial adaptation under highest TPH concentration; this would help in assessing the potential of a polluted soil to promote self-degradation of oil-derived hydrocarbon under natural or assisted remediation. The results highlighted the importance of the application of combined approach in the study of those parameters driving the soil amelioration and bioremediation.     

Phytoremediation in the tropics--influence of heavy crude oil on root morphological characteristics of graminoids

When studying species for phytoremediation of petroleum-contaminated soils, one of the main traits is the root zone where enhanced petroleum degradation takes place. Root morphological characteristics of three tropical graminoids were studied. Specific root length (SRL), surface area, volume and average root diameter (ARD) of plants grown in crude oil-contaminated and uncontaminated soil were compared. Brachiaria brizantha and Cyperus aggregatus showed coarser roots in polluted soil compared to the control as expressed in an increased ARD. B. brizantha had a significantly larger specific root surface area in contaminated soil. Additionally, a shift of SRL and surface area per diameter class towards higher diameters was found. Oil contamination also caused a significantly smaller SRL and surface area in the finest diameter class of C. aggregatus. The root structure of Eleusine indica was not significantly affected by crude oil. Higher specific root surface area was related to higher degradation of petroleum hydrocarbons found in previous studies.     

Incineration at Bayou Bonfouca Remediation Project

The Bayou Bonfouca hazardous waste site is located in Slidell, Louisiana, approximately 96 kilometers (60 miles) northeast of New Orleans. This site is ranked number 1,006 on the National Priorities List of Superfund sites. The U.S. Environmental Protection Agency (EPA) conducted a remedial investigation in 1986 and determined the primary potential exposure sources to be groundwater, surface waste piles, and contaminated sediment in Bayou Bonfouca. Based on the results of investigations, EPA and the Louisiana Department of Environmental Quality chose a remedy that involves dredging contaminated sediment from the bayou, excavating contaminated waste piles and soil, and incinerating the solid wastes in a transportable incinerator. The site remedy, which included incineration, was specified in the Record of Decision signed in March 1987.

Of the total 142,000 megagrams (Mg) (157,000 tons) of waste to be incinerated, approximately 119,000 Mg (132,000 tons) consist of hazardous sediment from the bayou; 22,600 Mg (25,000 tons) consist of lightly contaminated soils and waste piles, cellulosic materials, and other miscellaneous wastes on the ground. The solid wastes are primarily low heat content sediment and soils and cellulosic materials with polyaromatic hydrocarbon (PAH) concentrations from milligrams per kilogram (parts per million) levels up to two percent. The dredged bayou sediment will be dewatered in six, 115-cubiometer (150-cubic-yard) plate and frame filter presses before processing in the incinerator. A rotary-kiln-based single train incinerator is deployed at Bayou Bonfouca to process the solid waste feed.

On-site pilot studies indicated that the PAHs in groundwater could be removed by on-site pumping, treatment, and discharge of treated effluent to the bayou. The groundwater treatment plant went on-stream in June 1991. Treatment involves oil/water separation, filtration, carbon bed adsorption, and aeration.

IT Corporation-OH Materials, a joint venture, was awarded a contract in May 1991 and a notice to proceed in February 1992 to remediate and restore the Bayou Bonfouca site. The remediation project includes air quality monitoring and controls, site preparation, dredging and excavation, bayou bank stabilization and monitoring, equipment mobilization and erection, the trial burn, incineration, demobilization, and site closure. The project completed a successful trial burn in November 1993, and the commercial operation began in December 1993. The expected duration of the project is 40 months from mobilization to site closure.     

Remediation of metal-contaminated soils with the addition of materials--part I: characterization and viability studies for the selection of non-hazardous waste materials and silicates

Contamination episodes in soils require interventions to attenuate their impact. These actions are often based on the addition of materials to increase contaminant retention in the soil and to dilute the contaminant concentration. Here, non-hazardous wastes (such as sugar foam, fly ash and a material produced by the zeolitization of fly ash) and silicates (including bentonites) were tested and fully characterized in the laboratory to select suitable materials for remediating metal-contaminated soils. Data from X-ray fluorescence (XRF), N₂ adsorption/desorption isotherms, X-ray diffraction (XRD) and scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM-EDX) analyses revealed the chemical composition, specific surface area and the phases appearing in the materials. A pH titration test allowed the calculation of their acid neutralization capacity (ANC). The metal sorption and desorption capacities of the waste materials and silicates were also estimated. Sugar foam, fly ash and the zeolitic material were the best candidate materials. Sugar foam was selected because of its high ANC (17 000 meq kg⁻¹), and the others were selected because of their larger distribution coefficients and lower sorption reversibilities than those predicted in the contaminated soils.     

Age-dating Diesel Fuel Spills: Using the European Empirical Time-based Model in the U.S.A.

In 1993, a paper was published by Christensen and Larsen that offered a method for determining the age of diesel oil spills in soil (Christensen and Larsen, 1993 Ground Water Mount. R . Fall , 142-149). It presented an empirical time-based model of the degradation of diesel fuel in soils using chemical data gathered at petroleum release sites in Denmark and the Netherlands. Now, evaluation of the validity of the application of this work to subsurface petroleum releases in other countries remains. In the U.S.A., investigations assessing date(s) of release of diesel fuel in soils, e.g. age dating of subsurface petroleum contamination, have considerable interest. Litigation-driven scientific investigations with accompanying expert testimony in a court of law are underway. The number of instances where application of the Christensen and Larsen empirical time-based model to petroleum-contaminated properties is growing in the U.S.A. This paper presents two case studies which evaluate the applicability of the Christensen and Larsen empirical time-based model to petroleum-contaminated properties in general. It illustrates the approach using gas chromatographic data from two recently-completed projects evaluating the applicability of the Christensen and Larsen model to a No. 2 fuel oil/diesel fuel surface spill in the U.S.A. Results showed that the application of the model to petroleum-contaminated soils was scientifically valid, provided its applicability was evaluated using hypothesis testing for specific changes in the characteristics of the petroleum hydrocarbon distribution in a number of soil samples collected over time at one site. The paper offers observations on the application of the Christensen and Larsen model to petroleum found in the light non-aqueous phase liquid (LNAPL) phase and groundwater.     

Effect of temperature and particle size on the thermal desorption of PCBs from contaminated soil

Thermal desorption is widely used for remediation of soil contaminated with volatiles, such as solvents and distillates. In this study, a soil contaminated with semivolatile polychlorinated biphenyls (PCBs) was sampled at an interim storage point for waste PCB transformers and heated to temperatures from 300 to 600 °C in a flow of nitrogen to investigate the effect of temperature and particle size on thermal desorption. Two size fractions were tested: coarse soil of 420–841 μm and fine soil with particles <250 μm. A PCB removal efficiency of 98.0 % was attained after 1 h of thermal treatment at 600 °C. The residual amount of PCBs in this soil decreased with rising thermal treatment temperature while the amount transferred to the gas phase increased up to 550 °C; at 600 °C, destruction of PCBs became more obvious. At low temperature, the thermally treated soil still had a similar PCB homologue distribution as raw soil, indicating thermal desorption as a main mechanism in removal. Dechlorination and decomposition increasingly occurred at high temperature, since shifts in average chlorination level were observed, from 3.34 in the raw soil to 2.75 in soil treated at 600 °C. Fine soil particles showed higher removal efficiency and destruction efficiency than coarse particles, suggesting that desorption from coarse particles is influenced by mass transfer.     

Release of hexachlorocyclohexanes from historically and freshly contaminated soils in China: implications for fate and regulation

Hexachlorocyclohexanes (HCHs) were produced and used in large quantity worldwide and are common soil pollutants. In this study, desorption of α-HCH and γ-HCH from two soil samples collected from a historical pesticide plant in Tianjin, China, was examined. As a comparison, desorption of freshly sorbed γ-HCH was examined, using five typical Chinese soils. Strong resistant desorption was observed for both historically contaminated and freshly contaminated soils, and desorption results were well modeled with a biphasic desorption isotherm. The unique thermodynamic characteristics associated with the desorption-resistant fraction indicated that physical constraint within soil organic matrices was likely the predominant mechanism controlling resistant desorption. Resistant desorption could have significant effects on fate and exposure of HCHs in soil environment. More accurate biphasic desorption models that take into account of the resistant desorption can be used to facilitate regulating, management and remediation of HCH-contaminated sites.     

A Comparison of In situ Vitrification and Rotary Kiln Incineration for Soils Treatment

In the hazardous waste community, the term “thermal destruction” is a catchallphrase that broadly refers to high temperature destruction of hazardous contaminants. Included in the thermal destruction category are treatment technologies such as rotary kiln incineration, fiuidized bed incineration, infrared thermal treatment, wet air oxidation, pyrolytic incineration, and vitrification. Among them, conventional rotary kiln incineration, a disposal method for many years, is the most well established, and often serves as a barometer to gauge the relative success of similar technologies. Public sentiment on environmental issues and increasingly stringent environmental regulations has, over time, spurred design and development of innovative thermal treatment processes directed toward reducing harmful emissions and residuals that may require further treatment or disposal. In situ vitrification (ISV), a technology that combines heat and immobiliztion, is one such innovative and relatively new technology.

This paper presents a comparison of ISV and rotary kiln incineration for soils treatment in the areas of process performance, process residuals, process limitations, applicable or relevant and appropriate (ARAJRs) regulations, criteria and limitations, and costs.     

Stabilization of Heavy Metal Containing Hazardous Wastes with Byproducts from Advanced Clean Coal Technology Systems

ABSTRACT

The purpose of this investigation was to evaluate the success of residues from advanced Clean Coal Technology (CCT) systems as stabilization agents for heavy metal containing hazardous wastes. In the context examined here, stabilization refers to techniques that reduce the toxicity of a waste by converting the hazardous constituents to a less soluble, mobile, or toxic form.¹ Three advanced CCT byproducts were used: coal waste-fired circulating fluidized bed combustor residue, pressurized fluidized bed combustor residue, and spray drier residue. Seven metal-laden hazardous wastes were treated: three contaminated soils, two air pollution control dusts, wastewater treatment plant sludge, and sandblast waste. Each of the seven hazardous wastes was treated with each of the three CCT byproducts at dosages of 10, 30, and 50% by weight (byproduct:waste). The treatment effectiveness of each mixture was evaluated by the Toxicity Characteristic Leaching Procedure. Of the 63 mixtures evaluated, 21 produced non-hazardous residues. Treatment effectiveness can likely be attributed to mechanisms such as precipitation and encapsulation due to the formation of hydrated calcium silicates and calcium sulfo-alu-minates. Results indicate that these residues have potential beneficial uses to the hazardous waste treatment community, possibly substituting for costly treatment chemicals.     

不同处理条件对石油污染土壤植物修复的影响

针对石油烃植物修复过程中的主要影响因素,研究了不同植物种类、不同土壤调理剂和菌剂使用等不同条件对土壤中石油烃植物修复效果的影响.结果表明,不同种类的植物修复可使总石油烃的年降解率达到37.8％ ～ 73.98％,其中大豆和碱蓬具有较好的修复效果;3种不同土壤调理剂对石油烃污染土壤修复的效果为商业添加剂＞牛粪＞蛭石;先微生物修复后种植植物的处理要优于单独的微生物修复及微生物、植物修复同步进行的处理.     

Oxidation of polycyclic aromatic hydrocarbons by fungal isolates from an oil contaminated refinery soil

BACKGROUND AND OBJECTIVE: Indigenous soil microorganisms are used for the biodegradation of petroleum hydrocarbons in oily waste residues from the petroleum refining industry. The objective of this investigation was to determine the potential of indigenous strains of fungi in soil contaminated with petroleum hydrocarbons to biodegrade polycyclic aromatic hydrocarbons (PAH). MATERIALS AND METHODS: Twenty one fungal strains were isolated from a soil used for land-farming of oily waste residues from the petrochemical refining industry in Singapore and identified to genus level using laboratory culture and morphological techniques. Isolates were incubated in the presence of 30 mg/L of phenanthrene over a period of 28 days at 30 degrees C. The most effective strain was further evaluated to determine its ability to oxidise a wider range of PAH compounds of various molecular weight i.e acenaphthene, fluorene, fluoranthene, chrysene, benzo(a)pyrene and dibenz(ah)anthracene RESULTS AND DISCUSSION: After 28 days of incubation, 18 of the 21 fungal cultures were capable of oxidising over 50% of the phenanthrene present in culture medium, relative to abiotic controls. Fungal isolate, Penicillium sp. 06, was able to oxidise 89% of the phenanthrene present. This isolate could also oxidise more than 75% of the acenaphthene, fluorene and fluoranthene after 30 days of incubation. However, the oxidation of high molecular weight PAH i.e. chrysene, benzo(a)pyrene and dibenz(ah)anthracene by the Penicillium sp. 06 isolate was limited, where the extent of oxidation was inversely proportional to PAH molecular weight. CONCLUSIONS: Fungal isolate, Penicillium sp. 06, was effective at oxidising a range of PAH in petroleum contaminated soils, but higher molecular weight PAH were more recalcitrant. RECOMMENDATIONS AND OUTLOOK: There is potential for the re-application of this fungal strain to soil for bioremediation purposes.     

Advanced multivariate analysis to assess remediation of hydrocarbons in soils

Accurate monitoring of degradation levels in soils is essential in order to understand and achieve complete degradation of petroleum hydrocarbons in contaminated soils. We aimed to develop the use of multivariate methods for the monitoring of biodegradation of diesel in soils and to determine if diesel contaminated soils could be remediated to a chemical composition similar to that of an uncontaminated soil. An incubation experiment was set up with three contrasting soil types. Each soil was exposed to diesel at varying stages of degradation and then analysed for key hydrocarbons throughout 161 days of incubation. Hydrocarbon distributions were analysed by Principal Coordinate Analysis and similar samples grouped by cluster analysis. Variation and differences between samples were determined using permutational multivariate analysis of variance. It was found that all soils followed trajectories approaching the chemical composition of the unpolluted soil. Some contaminated soils were no longer significantly different to that of uncontaminated soil after 161 days of incubation. The use of cluster analysis allows the assignment of a percentage chemical similarity of a diesel contaminated soil to an uncontaminated soil sample. This will aid in the monitoring of hydrocarbon contaminated sites and the establishment of potential endpoints for successful remediation.     

Effects of chemical oxidation on sorption and desorption of PAHs in typical Chinese soils

In situ chemical oxidation is a commonly applied soil and groundwater remediation technology, but can have significant effects on soil properties, which in turn might affect fate and transport of organic contaminants. In this study, it was found that oxidation treatment resulted mainly in breakdown of soil organic matter (SOM) components. Sorption of naphthalene and phenanthrene to the original soils and the KMnO₄-treated soils was linear, indicating that hydrophobic partitioning to SOM was the predominant mechanism for sorption. Desorption from the original and treated soils was highly resistant, and was well modeled with a biphasic desorption model. Desorption of residual naphthalene after treating naphthalene-contaminated soils with different doses of KMnO₄ also followed the biphasic desorption model very well. It appears that neither changes of soil properties caused by chemical oxidation nor direct chemical oxidation of contaminated soils had a noticeable effect on the nature of PAH-SOM interactions.     

Conversion of chromium-containing solid wastes into value-added products through a plasma-assisted aluminothermic process

Chromium-containing solid wastes have been generated by chemical and leather/tanning industries, and the management and proper disposal of the same wastes have been challenging tasks. A significant fraction of these wastes contains chromium compounds with chromium present in the hexavalent (Cr⁺⁶) form, which is hazardous to human beings, animals, and ecosystems. Since these wastes are discarded largely without proper treatments, soil and groundwater get contaminated and they can cause several health issues to human beings. Conventional methods developed to convert hazardous Cr⁶⁺ to Cr³⁺/Cr metal either generate secondary toxic wastes and unwanted by-products and/or are time-consuming processes. In this work, a plasma-assisted aluminothermic process is developed to convert the toxic waste into non-toxic products. The waste was mixed with aluminium powder and subjected to transferred arc plasma treatment in a controlled air atmosphere. Chemical analysis and Cr leachability studies of the waste material prior to plasma treatment have shown that it is highly toxic. Analysis of the products obtained from the plasma treatment showed that Cr and Fe present in the waste could be recovered as a metallic mixture as well as oxide slag, which were found to be non-toxic. Easy separation of the metallic fraction and the slag from the treated product is one of the merits of this process. Besides converting chromium-containing toxic waste to non-toxic materials, the process is rapid and recovers the metals from the waste completely.