Effects of Weathering on Treatment of Lead Contaminated Soils

Treatment of lead-contaminated material focuses on the reduction of leached lead concentrations in laboratory leaching tests. There has been little study on the chemical stability of treated materials after waste disposal. To investigate the effects of weathering on several solidification/stabilization chemistries, lead-contaminated soil was treated with various agents (cement, phosphates, dithiocarbamate, calcium hydroxide, calcium carbonate, and metallic iron) and subjected to natural weathering for one year. Lead concentrations and pH values in field percolates and leachates from toxicity characteristic leaching procedure (TCLP) and water leaching tests were used to evaluate changes in the treatment effectiveness. Weathering altered the treatment chemistry of several additives—alkaline additives were neutralized, while reduced additives were oxidized. Lead concentrations in field percolates from the untreated soil were around 1.0?mg/L, and did not vary over one year of weathering time. After one year of weathering, lead concentrations in field percolates from most samples were reduced to low levels (<0.15 mg/L). Weathering also affected lead concentrations in the TCLP and water leach test leachates from the treated wastes. Treated wastes in which the alkaline additives were neutralized or reduced additives oxidized gave higher TCLP lead concentrations after weathering than before, in contrast to the decreasing lead concentrations in the field percolates. Water leaching tests on the alkaline treated wastes had lower lead concentrations after weathering than before.     

稀土配合物的激光诱导时间分辨荧光光谱研究

本文研究了RE(RE=DY、Eu、Sm、Tb)—HFA—TOPO—Triton X-100体系的激光诱导荧光光谱。拟定了时间分辨荧光光谱技术同时测定这四个稀土元素的分析方法,用于混合样品分析,获得了满意的结果。     

Electroremediation of Contaminated Soils

This paper presents a comprehensive review of the literature on electroremediation of soils. Laboratory studies of the technique are outlined, mechanisms of contaminant transport discussed, and major factors affecting the decontamination process examined. Enhancement techniques and hybrid processes are considered and examples of field trials and commercial applications described.     

Integrated System for Remediation of Contaminated Soils

A pilot-scale study was conducted to evaluate an integrated system for the remediation of soils contaminated primarily with pentachlorophenol (PCP), a wood preserver. The integrated soil remediation system consisted of three unit processes: (1) Soil solvent washing; (2) solvent recovery; and (3) biotreatment of the contaminant residual. Pilot-scale countercurrent solvent washing was carried out using a 95% ethanol solution—a solvent that in an earlier bench-scale study was found to be effective in removing PCP and hydrocarbons (HCs) from soils. Three-stage countercurrent solvent washing of a field-contaminated soil was performed using batches of 7.5 kg of soil and 30 L of solvent (1 kg:4 L soil-to-solvent contact ratio). The washed soil was rinsed with water in a single stage after three countercurrent wash stages. Pilot-scale, three-stage countercurrent solvent washing with 95% ethanol reduced the PCP and HC contamination on the soil by 98 and 95%, respectively. The spent solvent and the spent rinse water were combined as the spent wash fluid for further treatment. A pilot-scale distillation unit was used to recover the ethanol from the spent wash fluid. The HC constituents of the spent wash fluid were removed by pH adjustment prior to feeding the spent wash fluid to a distillation unit. Greater than 96% of the ethanol in the spent wash fluid was recovered in the distillate stream, whereas PCP was captured in the bottoms stream. The bottoms stream was treated sequentially in anaerobic and aerobic granular-activated carbon fluidized-bed reactors. Complete mineralization of PCP was achieved using this treatment train.     

Cosolvent-Enhanced Electrokinetic Remediation of Soils Contaminated with Phenanthrene

This research was carried out to evaluate feasibility of using an electrokinetic technique to remove hydrophobic organic pollutants from soils, with the assistance of a cosolvent (n-butylamine, tetrahydrofuran, or acetone) added to the conducting fluid. The experiments were carried out on glacial till clay with phenanthrene as the test compound. Desorption equilibrium was investigated by batch tests. The electrokinetic experiments were conducted using a 19.1 cm long × 6.2 cm inside diameter column under controlled voltage. Water or 20% (volume) cosolvent solution was constantly supplied at the anode. The concentration of phenanthrene in the effluent collected at the cathode was monitored. Each experiment lasted for 100 to 145 days. Results showed that the presence of n-butylamine significantly enhanced the desorption and electrokinetic transport of phenanthrene; about 43% of the phenanthrene was removed after 127 days or 9 pore volumes. The effect of acetone was not as significant as butylamine. The effluent flow in the tetrahydrofuran experiments was minimal, and phenanthrene was not detected in the effluent. The use of water as the conducting solution did not cause observable phenanthrene migration.     

Cyclodextrin-Enhanced Electrokinetic Remediation of Soils Contaminated with 2,4-Dinitrotoluene

The removal of 2,4-dinitrotoluene (2,4-DNT), a munitions waste constituent and an industrial intermediate, from contaminated soils was evaluated using enhanced electrokinetic (EK) remediation. Two model soils were spiked with 480?mg of 2,4-DNT/kg of dry soil for the EK experiments. The spiked soils were kaolin, a low-buffering clayey soil, and glacial till, a high-buffering silty soil. The glacial till was obtained from a field site and contained 2.8% organic matter. Deionized (DI) water and cyclodextrin solutions were used as the EK purging solutions. Cyclodextrin was selected as a nonhazardous solubility enhancer for enhancing the desorption and removal of 2,4-DNT from soils in EK remediation. Two aqueous solutions of hydroxypropyl β-cyclodextrin (HPCD) at concentrations of 1 and 2% were selected for kaolin and glacial till, respectively, based on results for batch extraction of 2,4-DNT from the same soils. During the EK experiments, greater current and electro-osmotic flow were observed for HPCD solutions than for DI water. After the completion of the EK experiments, the soils in the EK cell were extruded and the residual 2,4-DNT in the soils was determined. Less 2,4-DNT remained in the kaolin soil (up to 94% transformed) than in the glacial till soil (20% transformed) due to strong retention of 2,4-DNT by the soil organic matter in glacial till. For kaolin, less 2,4-DNT remained in the soil using HPCD solutions than using DI water. For glacial till, comparable levels of 2,4-DNT remained in the soil for both EK solutions. Since no 2,4-DNT was detected in the effluents from the EK cells, the decrease in 2,4-DNT concentration in the kaolin and glacial till soils was attributed to electrochemical transformation of 2,4-DNT to other species.     

Combined Particle Image Velocimetry/Planar Laser Induced Fluorescence for Integral Modeling of Buoyant Jets

Combined particle image velocimetry and planar laser induced fluorescence is an efficient measurement approach for laboratory studies in environmental hydraulics. The coupling of the two well-known techniques enables synchronized planar measurements of flow velocity and concentration in an area yielding both their mean distribution as well as turbulence covariance. In this paper, the merits and limitations of the combination are first discussed. An example of experimental setup is then briefly described. Finally, an application is demonstrated for the integral modeling of an inclined round buoyant jet that takes full advantage of the capability of the combined approach.     

土壤Cd-Zn复合污染修复技术研究进展

阐述了我国土壤重金属镉锌复合污染的来源、危害与污染现状,系统介绍了土壤中镉锌复合污染修复方法的研究进展,以及国内外镉锌污染修复技术应用情况,提出了镉锌复合污染土壤修复方法发展趋势。     

Enhanced Bioremediation of Fuel-Oil Contaminated Soils: Laboratory Feasibility Study

In this study, microcosm experiments were conducted to evaluate the effectiveness of (1) nutrients, hydrogen peroxide (H2O2), and cane molasses addition; (2) soil washing by biodegradable surfactant [Simple Green (SG)]; and (3) soil pretreatment by Fenton-like oxidation on the bioremediation of fuel-oil contaminated soils. The dominant native microorganisms in the fuel-oil contaminated soils after each treatment process were determined via polymerase chain reaction, denaturing gradient gel electrophoresis, and nucleotide sequence analysis. Results show that approximately 32 and 56% of total petroleum hydrocarbon (TPH) removal (initial concentration of 5,000?mg?kg?1) were observed in microcosms with the addition of nutrient and cane molasses (1,000?mg?L?1), respectively, compared to only 9% of TPH removal in live control microcosms under intrinsic conditions (without amendment) after 120 days of incubation. Addition of cane molasses would cause the increase in microbial population and thus enhance the TPH degradation rate. Results also show that approximately 61% of TPH removal was observed in microcosms with the addition of H2O2(100?mg?L?1) and nutrient after 120 days of incubation. This indicates that the addition of low concentration of H2O2(100?mg?L?1) would cause the desorption of TPH from soil particles and increase the dissolved oxygen and subsequent bioremediation efficiency in microcosms. Approximately 95 and 69% of TPH removal were observed in microcosms with SG (100?mg?L?1) and higher dose of H2O2(900?mg?L?1) addition, respectively. Moreover, significant increases in microbial populations were observed and two TPH biodegraders (Pseudomonas sp. and Shewanella sp.) might exist in microcosms with SG or H2O2 addition. This indicates that the commonly used soil remedial techniques, biodegradable surfactant flushing, and Fenton-like oxidation would improve the TPH removal efficiency and would not cause adverse effects on the following bioremediation process.     

Prediction of Metal Removal Efficiency from Contaminated Soils by Physical Methods

Six metal-contaminated soil samples were submitted to physical methods of treatment. A wet magnetic separator, Wilfley shaking table, and jig gravimetric separator were used on different soil fractions. A mineralogical model describing lead-bearing particles with and without iron oxide has been proposed. A significant part of the selected metals from each of the soil samples were removed by physical treatment. Linear regression analyses gave many relationships predicting the efficiency of the separation processes. The most useful variable to predict the magnetic process efficiency is the proportion of magnetic fraction removed. The density of fraction being removed was the most significant factor predicting the performance of the Wilfley table or the jig. The most significant variable predicting lead, copper, tin, and zinc removal was the initial metal concentration entering the process. Positive relationships between the results of the mineralogical study and the removal efficiency were found. These different relations confirm that the proposed scheme and the associated quantitative mineralogical study (identification of lead-bearing phase, carrying phase, and mean surface ratio of lead-bearing phase on total surface of lead-bearing particles) proved to be useful.     

Heat and Mass Transfer during Microwave Steam Treatment of Contaminated Soils

A time-dependent mechanistic model has been developed to describe the coupled heat and mass transfer during microwave steam treatment of contaminated soils. The model consists of multiphase mass and energy conservation equations, along with various temperature-dependent parameterizations of important physical state properties. The coupled nonlinear equations were solved numerically by applying a macroscopic control volume method with the appropriate boundary and initial conditions and using a finite-difference scheme. Microwave heating experiments of soil samples were performed. The effects of microwave power, soil sample depth, and soil type on water evaporation rate and temperature were measured with time. The modeled results are in good agreement with the experimental data. The results revealed that microwave power density and soil sample depth significantly affect the microwave evaporation process of water from soils. Water evaporation rate and temperature variation are complex and associated with the dielectric properties of liquid water distributed within the soil. The deeper the soil sample, the more nonuniform the evaporation process, although nonuniformities diminish as the evaporation process approaches completion. Finally it was verified that soil types and their thermal properties play a minor role, provided that the soil minerals are microwave transparent.     

Development of a Four-Phase Remedial Scheme to Clean Up Petroleum-Hydrocarbon Contaminated Soils

In this study, a four-phase remedial scheme was developed for in situ cleanup of petroleum-hydrocarbon contaminated soils. The developed remedial scheme contained the following four phases: surfactant flushing, groundwater flushing, chemical oxidation using KMnO4 as the oxidant, and enhanced bioremediation. Laboratory bench-scale experiments were performed to evaluate the effectiveness of this developed remedial scheme on the treatment of diesel oil contaminated soils. In the surfactant and groundwater flushing batch experiment (the first and second phases), biodegradable surfactant, Simple Green (SG) (5% by weight) was applied to flush diesel oil contaminated soils with initial total petroleum-hydrocarbon (TPH) concentration of approximately 31,500??mg?kg-1. Results show that more than 90% of TPH could be removed after flushing with 40 pore volumes (PVs) of SG, followed by 25?PVs of groundwater. In the KMnO4 oxidation experiment (third phase) with initial soil TPH concentration at approximately 4,900??mg?kg-1, up to 65% of TPH removal efficiency can be obtained when 1% by weight of KMnO4 was applied for oxidation. Results also reveal that the slight increase in TPH removal was observed in experiments with SG addition (0.1% by volume) owing to increased dissolution and desorption of TPH from soils. In the enhanced bioremediation (fourth phase) batch experiments, a petroleum-hydrocarbon degrading bacterium was isolated from the soil materials after the KMnO4 oxidation experiments and identified as Pseudomonas sp. via biochemical tests and further confirmation of DNA sequencing. Results from biodegradation experiments indicate that the isolated bacterium, which survived after KMnO4 oxidation process, was capable of degrading TPH caused by diesel oils, and caused the TPH to drop from 2,105 to 487??mg?kg-1 within 15?days of incubation. The effectiveness of the four-phase remedial scheme was further confirmed by a semicontinuous batch experiment. Results from this study indicate that the four-phase scheme is a promising technology for the treatment of petroleum-hydrocarbon contaminated soils.     

Consolidation Behavior of Soils Subjected to Asymmetric Initial Excess Pore Pressure Distributions

Although the consolidation settlements beneath foundations and embankments are rarely one dimensional, Terzaghi’s one-dimensional consolidation theory is often applied to these situations to approximate consolidation behavior. This paper investigates the consolidation behavior of a soil stratum subjected to various initial excess pore pressure distributions which occur under one-dimensional loading. The results show that analysis in terms of average degree of consolidation provides an incomplete representation of the consolidation behavior. While the average degree of consolidation curves for all uniform and linearly varying initial distributions are identical, the degree of consolidation isochrones for each distribution are unique. Furthermore, the application of a bottom-skewed initial excess pore pressure distribution results in a redistribution of pore pressures toward the skewed region so that an increase in excess pore pressure occurs at some depth after consolidation has already commenced. As a result, conventional consolidation relationships are considered inappropriate for these cases, and an alternative method of consolidation analysis in terms of normalized pore pressures is proposed.     

Treatment of Fuel-Oil Contaminated Soils by Biodegradable Surfactant Washing Followed by Fenton-Like Oxidation

Among petroleum-hydrocarbon pollutants, fuel-oil is more difficult to treat compared to gasoline and diesel fuel. The objectives of this bench-scale study were to: (1) develop a two-stage remedial system consisting of surfactant washing followed by Fenton-like oxidation process to remediate fuel-oil contaminated soils; (2) evaluate the effects of residual surfactant and soil organic matter (SOM) on the efficiency of Fenton-like oxidation; (3) evaluate the effect of potassium dihydrogen phosphate (KH2PO4) addition on the stability of H2O2 and oxidation efficiency; and (4) evaluate the possible oxidation products after the oxidation process. In the surfactant washing stage, biodegradable surfactant, Simple Green (SG) (50?g?L?1), was applied to flush fuel-oil contaminated soils with initial total petroleum-hydrocarbons (TPHs) concentration of 50,000?mg?kg?1. Results show that approximately 90% of TPH could be removed after washing with 45 pore volumes (PVs) of SG followed by 25 PVs of deionized water, while the soil TPH concentration dropped from 50,000 to 4,950?mg?kg?1. In the Fenton-like oxidation stage with initial soil TPH concentration was approximately 4,950?mg?kg?1, TPH removal efficiency can be significantly increased with increased H2O2 concentrations. Results also reveal that residual SG and SOM would compete with TPH for oxidants and cause the decrease in oxidation efficiency. An “oxidation-sorption-desorption-oxidation” scheme for soil TPH was observed in this experiment due to the initial sorption of TPH on SOM. Results show that an addition of 2.2 mM of KH2PO4 could increase the stability and half-life of H2O2, but caused the decrease in TPH removal efficiency. The oxidation potential of Fenton-like process was not capable of completely oxidizing fuel-oil to nontoxic end products. The observed by-products after oxidation process contained carboxyl groups with molecular weights similar to their parent compounds. Results from this study indicate that the two-stage remedial system is a promising technology for fuel-oil contaminated soil treatment.     

Laboratory-Scale Flotation Process for Treatment of Soils Contaminated with Both PAH and Lead

A soil decontaminating process has been studied at laboratory scale for the treatment of one soil polluted by both polycyclic aromatic hydrocarbons (PAHs) and lead (Pb). This process first includes attrition and sieving steps to separate the coarse (>2?mm) from the fine (<2?mm) fractions, followed by a flotation step using an amphoteric surfactant in acid and saline conditions for the treatment of the fine contaminated particles. Electrodeposition and chemical precipitation using sodium hydroxide have been compared to ensure a possible reuse of wastewaters without disturbing the efficiency of the process. The performance of the process has been estimated considering soil quality after treatment with respect to the limit regulatory levels for commercial or industrial use in Quebec (Canada). Precipitation of lead hydroxides was efficient after five cycles of wastewaters reuse, while electrodeposition did not maintain efficiency of the flotation step with regard to PAH levels in soil after treatment. The complete process including Pb precipitation ensured the removal of 89±8 and 76±10% of total PAH, respectively, for the coarse (>2?mm) and fine (<2?mm) fractions, while Pb was removed at 88±10 and 65±2%, respectively, for the same fractions of the soil.     

Application of Fluorescence Technique for Rapid Identification of DOM Fractions in Source Waters

Dissolved organic carbon has been typically used as a measure of organic content in source waters. However, dissolved organic carbon is an aggregate parameter and does not provide information on the organic character of natural organic matter in water. The spectral fluorescent signatures technique coupled with a multiple linear regression model was applied for the rapid identification of six dissolved organic matter (DOM) fractions (hydrophobic acid, hydrophobic neutral, hydrophobic base, hydrophilic acid, hydrophilic neutral, and hydrophilic base) along a major river in a New Jersey watershed. The technique∕model enabled rapid spatial and temporal determination for the rapid qualitative and quantitative measurement of the DOM fraction(s) in the river. The analysis of DOM fractions also enables screening of the watershed for variations in humic and nonhumic substances input/output along the reaches.     

螯合剂诱导五节芒强化修复铀污染土壤

以典型铀矿山周边铀污染土壤为研究对象,采用盆栽试验,以五节芒为试验材料,研究乙二胺四乙酸(EDTA)、柠檬酸(CA)、乙二胺二琥珀酸(EDDS)等不同浓度螯合剂(0、2.5、5.0、7.5 mmol/kg)对五节芒修复铀污染土壤的影响。结果表明,五节芒的生长及富集吸收铀与螯合剂浓度及种类有关。EDTA对五节芒有明显的毒害作用,随浓度的提高消极影响越大,修复效果不理想;2.5 mmol/kg和5.0 mmol/kg的CA与EDDS均可促进五节芒的生长和富集吸收铀的效果,但CA效果优于EDDS,CA在5.0 mmol/kg处理组时,地上、根部生物量分别增加27.06%、12.88%,铀富集量分别提高68.05%、43.21%,且根部的铀含量远远大于地上部,说明螯合剂促进土壤溶液中残渣态铀逐渐向活性态铀转换,促进了植物的吸收富集。     

Remediation of Contaminated Soils with PCBs Using an Integrated Treatment: Desorption and Oxidation

During most of the past century, large quantities of substances were produced and utilized that subsequently proved harmful. This is the case with polychlorinated biphenyls (PCBs) which only became prohibited by law in the 1970s. As a result of their physicochemical properties, these substances are now present everywhere, although they are mainly found in soils, since they are hydrophobic in character. The present study evaluates an innovatory treatment for the remediation ex situ of soils contaminated by PCBs. This treatment consists of a first stage of desorption using a surfactant agent, followed by a second stage of oxidation with the object of transforming the PCBs into innocuous substances through successive oxidations using the photo-Fenton process. The results obtained (87% remediation in the desorption and 100% in the oxidation stages) show this new treatment to be a highly effective alternative, which does not generate dangerous residues of any type.     

Comparison of Potassium Permanganate and Hydrogen Peroxide as Chemical Oxidants for Organically Contaminated Soils

Laboratory experiments were completed to compare the treatment efficiency of KMnO4 with H2O2 (alone or with amendments) for sand and silty clay soil contaminated with either a mixture of volatile organic compounds (VOCs) [trichloroethylene (TCE), tetrachloroethene (PCE), and 1,1,1-trichloroethane (TCA)] or semivolatile organic compounds (SVOCs) (naphthalene, phenanthrene, and pyrene). The relatively treatment effects of soil type, oxidant loading rate and dosing, and reaction period, as well as the use of surfactant or iron amendments and pH adjustment were examined using batch experiments with contaminated soil slurries. When KMnO4 was applied to low organic carbon, acidic, or alkaline soils, at loading rates of 15–20 g∕kg it was found to degrade consistently 90% or more of the alkene VOCs (TCE and PCE) and 99% of the polyaromatic SVOCs (naphthalene, pyrene, and phenanthrene). H2O2 was more sensitive to contaminant and soil type and VOC treatment efficiencies were somewhat lower as compared with KMnO4 under comparable conditions, particularly with the sandy soil and even when supplemental iron was added. In clay soil, H2O2 with iron addition degraded over 90% of the SVOCs present compared with near zero in sandy soil, unless the pH was depressed to pH 3 and iron amendments were increased, whereby the treatment efficiency in the sandy soil was increased slightly. With both H2O2 and KMnO4, treatment efficiency increased to varying degrees as the oxidant loading rate (g∕kg) and reaction time (h) were increased. Multiple oxidant additions or surfactant addition were not found to have any significant effect on VOC treatment efficiency. Also, very limited TCA treatment was observed with either H2O2 or KMnO4.     

Clean up of Petroleum-Hydrocarbon Contaminated Soils Using Enhanced Bioremediation System: Laboratory Feasibility Study

The objective of this study was to assess the potential of applying enhanced bioremediation on the treatment of petroleum-hydrocarbon contaminated soils. Microcosm experiments were conducted to determine the optimal biodegradation conditions. The control factors included oxygen content, nutrient addition, addition of commercially available mixed microbial inocula, addition of wood chip and rice husk mixtures (volume ratio = 1:1) as bulking agents, and addition of organic amendments (chicken manures). Results indicate that the supplement of microbial inocula or chicken manures could significantly increase the microbial populations in soils, and thus enhance the efficiency of total petroleum hydrocarbon (TPH) removal (initial TPH = 5,500?mg/kg). The highest first-order TPH decay rate and removal ratio were approximately 0.015?day?1 and 85%, respectively, observed in microcosms containing microbial inocula (mass ratio of soil to inocula = 50:1), nutrient, and bulking agent (volume ratio of soil to bulking agent = 10 to 1) during 155 days of incubation. Results indicate that the first-order TPH decay rates of 0.015 and 0.0142?day?1 can be obtained with the addition of microbial inocula and chicken manures, respectively, compared with the decay rate of 0.0069?day?1 under intrinsic conditions. Thus, chicken manures have the potential to be used as substitutes of commercial microbial inocula. The decay rate and removal ratio can be further enhanced to 0.0196?day?1 and 87%, respectively, with frequent soil shaking and air replacement. Results will be useful in designing an ex situ soil bioremediation systems (e.g., biopile and land farming) for practical application.