Enhanced Soil Flushing for Simultaneous Removal of PAHs and Heavy Metals from Industrial Contaminated Soil

Polycyclic aromatic hydrocarbons (PAHs) and heavy metals are environmental concerns and must be removed to acceptable levels. This paper evaluates different flushing agents to enhance the remediation of soil contaminated with PAHs and heavy metals at a former manufactured gas plant site. Four flushing column tests at a constant hydraulic gradient of 1.2 were conducted using four different flushing agents, which included deionized water, chelant (0.2?M EDTA), surfactant (5% Igepal CA-720), and cyclodextrin (10% hydroxypropyl-β-cyclodextrin or HPCD). Additional column tests using Igepal and HPCD at a lower hydraulic gradient of 0.2 were conducted to investigate the effects of rate-limited desorption or solubilization of PAHs. The results showed that the EDTA produced the maximum metal removal from the soil compared with deionized water, Igepal, and HPCD under different hydraulic gradient conditions. The 0.2?M EDTA flushing solution removed approximately 25–75% of the toxic heavy metals found in the soil. None of the PAHs were removed from the soil when deionized water and EDTA were the flushing solutions. The PAHs removal efficiencies in the Igepal and HPCD systems decreased as the hydraulic gradient decreased. However, the surfactant-enhanced systems were more efficient in removing PAHs from the soil than the HPCD systems under high- and low-hydraulic gradients. The results also demonstrated that the removal of PAHs in surfactant-enhanced systems depended upon the micelles formation, whereas in the HPCD-enhanced systems, it depended upon the sterioselective diffusion of the PAHs to the nonpolar cavity of the HPCD. Overall, this study showed that the contaminant removal in soil flushing systems depends on the flushing solution affinity and selectivity toward the target contaminant and the existing hydraulic gradient condition.     

Lead Extraction from Contaminated Soil Using Water-Soluble Polymers

The applicability of water-soluble polymers as extractants for the remediation of heavy metal-contaminated soils has been explored using a lead-contaminated Superfund soil as a sample system. Polyethylenimine (PEI) was functionalized with bromo- or chloroacetic acid to give an aminocarboxylate chelating group, which effectively binds lead. The resulting polymer, PEIC, has extraction properties similar to the molecular chelator ethylenediaminetetraacetic acid. A series of studies was done to probe optimum conditions for lead extraction from soils obtained from the Cal-West Superfund site in New Mexico that contained approximately 10,000 ppm of Pb. In batch extraction experiments using polymer functionalized at two different levels, the polymers removed greater than 97% of the lead from the soils. Subsequent experiments demonstrated that the selective extraction of lead could be controlled by varying polymer functionalization levels. Concentration and regeneration of the polymers using ultrafiltration was also demonstrated. Release of lead from the polymer was accomplished by acidification to pH 1 with HCl. Subsequent ultrafiltration allowed recovery of the extractant polymer for reuse.     

Enhanced Electrokinetic Remediation of Heavy Metals in Glacial Till Soils Using Different Electrolyte Solutions

Previous electrokinetic remediation studies involving the geochemical characterization of heavy metals in high acid buffering soils, such as glacial till soil, revealed significant hexavalent chromium migration towards the anode. The migration of cationic contaminants, such as nickel and cadmium, towards the cathode was insignificant due to their precipitation under the high pH conditions that result when the soil has a high acid buffering capacity. Therefore the present laboratory study was undertaken to investigate the performance of different electrolyte (or purging) solutions, which were introduced to either dissolve the metal precipitates and/or form soluble metal complexes. Tests were conducted on a glacial till soil that was spiked with Cr(VI), Ni(II), and Cd(II) in concentrations of 1,000, 500, and 250 mg/kg, respectively, under the application of a 1.0 VDC/cm voltage gradient. The electrolyte solutions tested were 0.1M EDTA (ethylenediaminetetraacetic acid), 1.0M acetic acid, 1.0M citric acid, 0.1M NaCl/0.1M EDTA, and 0.05M sulfuric acid/0.5M sulfuric acid. The results showed that 46–82% of the Cr(VI) was removed from the soil, depending on the purging solution used. The highest removal of Ni(II) and Cd(II) was 48 and 26%, respectively, and this removal was achieved using 1.0M acetic acid. Although cationic contaminant removal was low, the use of 0.1M NaCl as an anode purging solution and 0.1M EDTA as a cathode purging solution resulted in significant contaminant migration towards the soil regions adjacent to the electrodes. Compared to low buffering capacity soils, such as kaolin, the removal of heavy metals from the glacial till soil was low, and this was attributed to the more complex composition of glacial till. Overall, this study showed that the selection of the purging solutions for the enhanced removal of heavy metals from soils should be primarily based upon the contaminant characteristics and the soil composition.     

Heavy Metals Removal from Acidic and Saline Soil Leachate Using Either Electrochemical Coagulation or Chemical Precipitation

This study compares electrocoagulation and chemical precipitation for heavy metals removal from acidic soil saline leachate (SSL) at the laboratory pilot scale. The electrocoagulation process was evaluated via an electrolytic cell [12 cm (width)×12 cm (length)×19 cm (depth)] using mild steel electrodes (10 cm width×11 cm high), whereas chemical precipitation was evaluated using either calcium hydroxide [Ca(OH)2] or sodium hydroxide (NaOH). By comparison with chemical precipitation at a pH varying between 7 and 8, electrocoagulation was more effective in removing metals from SSL having a relatively low contamination level (124?mg?Pb/L and 38?mg?Zn/L). For SSL enriched with different heavy metals (each concentration of metals was initially adjusted to 100 mg/L) and treated at a pH lower than 8.5, with the exception of Cd, the residual metal concentrations at the end of the experiments were below the acceptable level recommended for effluent discharge in urban sewage works (less than 4 mg/L of each residual metal concentration was recorded) using electrocoagulation, contrary to chemical precipitation using NaOH (more than 15 mg/L of each residual metal concentration was recorded). By comparison, chemical precipitation using Ca(OH)2 was effective in reducing Cr, Cu, Ni, and Zn under the permissive level, but not for Cd and Pb. However, both chemical precipitation processes needed to be operated at higher pH values (around 10.0) to be more effective in reducing metals from SSL and, therefore, required a pH adjustment of the effluent before discharge, whereas electrochemical treatment had a practical advantage of producing an effluent having a pH close to the neutral value and suitable for stream discharge in the receiving water. On the other hand, electrocoagulation was also found to be very efficient for removing Pb from very contaminated solutions (250–2,000 mg?Pb/L). At least 94% of Pb was removed regardless of the initial Pb concentration in the SSL. Electrochemical coagulation involves a total cost varying from 8.67 to 13.00 $/tds, whereas 0.84 to 16.73 $/tds is recorded using chemical precipitation. The cost included only energy consumption, chemicals consumption, and metallic sludge disposal.     

Selective Removal of Heavy Metals from Industrial Wastewater Using Maghemite Nanoparticle: Performance and Mechanisms

This study investigated the applicability of maghemite (γ-Fe2O3) nanoparticles for the selective removal of toxic heavy metals from electroplating wastewater. The maghemite nanoparticles of 10?nm were synthesized using a sol–gel method and characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The surface area of the nanoparticles was determined to be 198?m2/g using the Brunauer–Emmett–Teller method. Batch experiments were carried out to determine the adsorption kinetics and mechanisms of Cr(VI), Cu(II), and Ni(II) by maghemite nanoparticles. The adsorption process was found to be highly pH dependent, which made the nanoparticles selectively adsorb these three metals from wastewater. The adsorption of heavy metals reached equilibrium rapidly within 10?min and the adsorption data were well fitted with the Langmuir isotherm. Regeneration studies indicated that the maghemite nanoparticles undergoing successive adsorption–desorption processes retained original metal removal capacity. Mechanism studies using TEM, XRD, and X-ray photoelectron spectroscopy suggested that the adsorption of Cr(VI) and Cu(II) could be due to electrostatic attraction and ion exchange, and the adsorption of Ni(II) could be as a result of electrostatic attraction only.     

Experimental Studies on Heavy Metal Extraction from Contaminated Soil Using Ammonium Citrate as Alkaline Chelate during the Electrokinetic Process

Researchers have performed experimental studies using ammonium citrate (AC) during the electrokinetic (EK) remediation process for the extraction of cadmium (Cd) and copper (Cu) from the contaminated soil. They evaluated the efficiency of ammonium citrate by considering it as a washing solution and a purging solution at the anode electrode compartment. The efficiency of electrokinetic extraction was observed to be significantly influenced by the pH and buffering nature of the soil medium. The experimental studies indicate that the removal of cadmium and copper was 48.9% and 30.0%, respectively, when ammonium citrate was used both washing and purging solution. The solubility of both cadmium (Cd++) and copper (Cu++) in EK-treated soils has also been estimated by sequential extraction studies with deionized (DI) water. The analytical techniques, X-ray diffraction (XRD), X-ray fluorescence (XRF), and scanning electron microscope (SEM) provide the evidence of migration of cations during treatment of contaminated soil by process of electroosmosis (EO). The SEM images of both cadmium- and copper-contaminated soils show that these soils have a fluffier and more porous structure. This might be caused by the change in surface charges of the clay particles as a result of introduction of heavy metals. The mineralogical compositions of soil are not altered significantly by electrokinetic process.     

Evaluation of Electrokinetic Removal of Heavy Metals from Tailing Soils

Electrokinetic remediation was studied for the removal of toxic heavy metals from tailing soils. The study emphasized the dependency of removal efficiencies upon their speciations, as demonstrated by the different extraction methods used, which included sequential extraction, total digestion, and 0.1 N HCl extraction. The tailing soils examined showed different physicochemical characteristics, such as initial pH, particle size distribution, and major mineral constituents, and they contained high concentrations of target metal contaminants in various forms. The electrokinetic removal efficiencies of heavy metals were significantly influenced by their partitioning prior to treatment, and the pHs of the tailing soils. The mobile and weakly bound fractions of heavy metals, such as the exchangeable fraction, were easily removed by electrokinetic treatment (more than 90% removal efficiency), but immobile and strongly bound fractions, such as the organically bound species and residual fractions, were not significantly removed (less than 20% removal efficiencies).     

Evaluating an Electrokinetically Driven Extraction Method for Measuring Heavy Metal Soil Contamination

Measuring the heavy metal burden of “old contamination” soils (soils with aged contamination) can be challenging. Many laboratory procedures are currently in use and these can yield a wide range of burden estimates for the same soil. The appropriate extraction method selection depends on the intended use of the information and on compatibility with the procedures used to generate the “reference” data to which results are compared. In this work, results for an extraction based on the electrokinetic mobilization of old contamination heavy metals were compared to the results of established single analyte and sequential extraction methods. Accomplishing extractions electrokinetically offers promise for simplifying processes and for evaluating the electrokinetic remediation potential of old contamination soils. On the brownfield soils tested, electrokinetic extraction identified an average of 82% of the soil’s Cr, Cu, Pb, and Zn burden relative to Environmental Protection Agency Method 3050B extractions. However, results also indicated that neither of these methods were successful at extracting all of the sequestered (residual) fraction of heavy metals and thus underestimated the total contamination burden of the soil.     

Cadmium Release from Four Sorbents during Treatment of Contaminated Soils by Catalyzed H2O2 Propagations (Modified Fenton’s Reagent)

The release of heavy metals from soils and subsurface solids is a significant concern during in situ chemical oxidation treatment. The release of cadmium sorbed on four solids of varied properties was investigated in slurries treated by catalyzed H2O2 propagations (CHP—modified Fenton’s reagent). Cadmium was released in all four solids in CHP reactions conducted at pH 3; however, aqueous cadmium concentrations decreased in CHP reactions conducted at pH 7. Cadmium release at pH 3 was directly proportional to the soil organic carbon (SOC) content of the four solids (R2 = 0.99), and may have been due to destruction of the SOC by hydroxyl radical in the reactions at pH 3. Scavenging of hydroxyl radical minimized the release of cadmium in CHP systems at pH 3, which is consistent with cadmium release resulting from destruction of SOC by hydroxyl radical. Scavenging of hydroxyl radical in CHP systems at pH 7 resulted in increased cadmium release, compared to pH 7 reactions without the hydroxyl radical scavenger isopropanol. Superoxide, the conjugate base of perhydroxyl radical (pKa = 4.8), was proposed as the desorbing species in the scavenged CHP reactions at pH 7. The results of this research demonstrate that cadmium release will likely be minimal in CHP reactions conducted at pH 7 if compounds that increase the activity of superoxide are not present at significant concentrations.     

Complicating Factors of Using Ethylenediamine Tetraacetic Acid to Enhance Electrokinetic Remediation of Multiple Heavy Metals in Clayey Soils

Batch and electrokinetic experiments were conducted to investigate the removal of three different heavy metals, chromium(VI), nickel(II), and cadmium(II), from a clayey soil by using ethylenediamine tetraacetic acid (EDTA) as a complexing agent. The batch experiments revealed that high removal of these heavy metals (62–100%) was possible by using either a 0.1?M or 0.2?M EDTA concentration over a wide range of pH conditions (2–10). However, the results of the electrokinetic experiments using EDTA at the cathode showed low heavy metal removal efficiency. Using EDTA at the cathode along with the pH control at the anode with NaOH increased the pH throughout the soil and achieved high (95%) Cr(VI) removal, but the removal of Ni(II) and Cd(II) was limited due to the precipitation of these metals near the cathode. Apparently, the low mobility of EDTA and its migration direction, which opposed electroosmotic flow, prevented EDTA complexation from occurring. Overall, this study found that many complicating factors affect EDTA-enhanced electrokinetic remediation, and further research is necessary to optimize this process to achieve high contaminant removal efficiency.     

Nitric Oxide Emission and Soil Microbial Activities in Toluene Contaminated Soil

The purpose of this research is to consider a novel concept for measuring and monitoring (M&M) the presence and levels of contaminants in soil. Current M&M techniques include direct sensing for the target contaminant and the surrogate indicators of respired O2 and CO2. The method suggested here is based on nitric oxide (NO). It is an alternative M&M method that could become quicker, easier, more reliable, and less expensive than the other M&M methods being used currently. NO emission from toluene contaminated soil and soil microbial activity were investigated to understand the NO-toluene-soil microbial relationships using fluorescent in situ hybridization molecular technique combined by enzymatic method. The relationships have been analyzed by the comparison of experimental measurements coming from analysis of variance statistical analysis, referring to toluene concentrations. Relationships between NO emissions and the microbial activity were significantly correlated (P<0.01) with the level of toluene concentration and duration of toluene contamination. Thus, NO emissions are suggested as a useful indicator of microbial activity in toluene contaminated soils.     

Study on Pb and PAHs Emission Levels of Heavy Metals- and PAHs-Contaminated Soil during Thermal Treatment Process

The objective of this study was to use thermal treatment to treat soil contaminated with heavy metals and polycyclic aromatic hydrocarbons (PAHs). The emissions of lead (Pb) and PAHs during the thermal treatment process were evaluated. The parameters included pretreatment, temperature, and speed of the rotary kiln. Cadmium (Cd) had a higher mobility in thermally treated contaminated soil slag than other heavy metals because the primary fraction of Cd was the exchangeable fraction (90%). Of the temperatures tested in this study, the highest emission concentration of Pb occurred at 700°C. The Pb emission concentrations in the gas phase and solid phase were 44?μg/N?m3 and 138.35?μg/N?m3, respectively. In PAHs emissions, naphthalene, acenaphthene (Acp), and fluorene were the main species in the gas phase, at different operating temperatures. The concentrations of these species ranged from 615.5 to 2,002.3?μg/N?m3. Acp and chrysene were the main species in the solid phase at different temperatures, and the concentrations of these species ranged from 25.5 to 113?μg/N?m3.     

Sequentially Enhanced Electrokinetic Remediation of Heavy Metals in Low Buffering Clayey Soils

This paper presents the results of an experimental investigation undertaken to evaluate different purging solutions to enhance the removal of multiple heavy metals, particularly chromium, nickel, and cadmium, from a low buffering clay, specifically kaolin, during electrokinetic remediation. Experiments were conducted on kaolin spiked with Cr(VI), Ni(II), and Cd(II) in concentrations of 1,000, 500, and 250 mg/kg, respectively, which simulate typical electroplating waste contamination. A total of five different tests were performed to investigate the effect of different electrode purging solutions on the electrokinetic remedial efficiency. A constant DC voltage gradient of 1 V/cm was applied for all the tests. The removal of heavy metals from the soil using tap water as the purging solution was very low. When 1 M acetic acid was used as the purging solution in the cathode, the removal of chromium, nickel, and cadmium was increased to 20, 19, and 13%, respectively. Using 0.1 M ethylene diamine tetraacetic acid as the purging solution in the cathode, 83% of the initial Cr was removed; however, the nickel and cadmium removal was very low. A sequentially enhanced electrokinetic remediation approach involving the use of water as a purging solution at both the anode and cathode initially, followed by the use of acetic acid as the cathode purging solution and a NaOH alkaline solution as the anode purging solution was tested. This sequential approach resulted in a maximum removal of chromium, nickel, and cadmium of 68–71, 71–73, and 87–94%, respectively. This study shows that the sequential use of appropriate electrode purging solutions, rather than a single electrode purging solution, is necessary to remediate multiple heavy metals in soils using electrokinetics.     

我国有色金属工业土壤重金属污染防治的现状与对策

我国是有色金属生产大国。有色金属产业发展带来的环境问题,特别是土壤重金属污染的防治,是土壤污染防治中的重点领域。目前,我国就土壤重金属污染防治出台了一系列法规政策,对有色金属工业土壤重金属污染防治工作提出了具体要求。但是,总体看来,我国有色金属工业土壤重金属污染防治工作仍然面临着严峻的形势。进一步贯彻相关法规政策,建立健全体制机制,促进相关领域技术创新,通过机制推动促进产业发展等,均是"十四五"时期该领域发展中应当重视的问题。     

Modeling Elution Histories of Copper and Lead from Contaminated Soil Treated by Poly(amidoamine) Dendrimers

A dynamic “two-site” model was formulated and tested for simulating the elution histories of copper (Cu2+) and lead (Pb2+) from a contaminated soil treated by poly(amidoamine) dendrimers. In the model, the metal sorption sites of the soil were divided into two compartments: one with a fast desorption rate and the other with a slow desorption rate. The model was tested for simulating and predicting Cu2+ and Pb2+ elution histories obtained from column experiments. Compared to the classical “one-site” model and the modified “gamma distribution” model, the “two-site” model not only provides much improved power for simulating the observed metal elution data, but also can more accurately predict the metal elution histories under various experimental conditions including initial metal concentration in soil, dendrimer concentration, and pH.     

Migration of Heavy Metals in Saturated Sand and Bentonite/Soil Admixture

Heavy metal migration through compacted, saturated sand and bentonite/soil admixtures were investigated using kinetic, batch sorption tests, and column tests. Sorption of Pb, Zn, and Cd at pH 5 by bentonite is found to be 411.2, 163.4, and 71.8 mL/g, respectively. The permeability of the compacted sand (8×10?4?cm/s) is found to be 6 orders of magniture higher than that of bentonite/soil admixture (about 8×10?10?cm/s) when permeated with metal solutions under an effective stress of 34.5 kPa (5 psi). The permeation of metal solutions into bentonite/soil admixture columns does not result in a significant increase in permeability. Experimental results of batch sorption and hydraulic conductivity tests were also analyzed with a computer-based simulation model, POLLUTE, to determine the transport parameters (effective porosity, dispersion coefficient, retardation) of chloride ions and heavy metals in a homogeneous compacted sand and bentonite/soil admixture using a curve fitting technique.     

Screening Level Risk Assessment of Heavy Metal Contamination in Cleveland Area Commons

Commons are public lands that are often used for recreational activities and are generally assumed to be free of soil contamination. However, in old industrial cities, urban commons may have accumulated heavy metal burdens from airborne contamination. This paper examines the heavy metal burdens and risk analysis results for 50 commons in the greater Cleveland, Ohio area. The U.S. Environmental Protection Agency Method 3050B and 1N HCl soil extraction results are presented for Cd, Cr, Cu, Ni, Pb, and Zn mass burdens, and are interpreted relative to Ohio residential soil guidance and “typical” values from the remediation guidance of 30 states. Results demonstrate that most of these soils have heavy metal burdens that are well above naturally occurring levels, and several (at least 8 of the 50 sites tested) have heavy metal burdens that exceed Ohio’s residential soil contamination guidance. Lead and cadmium were found to be the most significant contributors to site hazard index values.     

Evaluating the Mobility of Arsenic in Synthetic Iron-Containing Solids Using a Modified Sequential Extraction Method

Many water treatment technologies for arsenic removal that are used today produce arsenic-bearing residuals which are disposed in nonhazardous landfills. Previous works have established that many of these residuals will release arsenic to a much greater extent than predicted by standard regulatory leaching tests (e.g., the toxicity characteristic leaching procedure) and, consequently, require stabilization to ensure benign behavior after disposal. In this work, a four-step sequential extraction method was developed in an effort to determine the proportion of arsenic in various phases in untreated as well as stabilized iron-based solid matrices. The solids synthesized using various potential stabilization techniques included: amorphous arsenic-iron sludge (ASL), reduced ASL via reaction with zero valent iron (RASL), amorphous ferrous arsenate (PFA), a mixture of PFA and SL (M1), crystalline ferrous arsenate (HPFA), and a mixture of HPFA and SL (M2). The overall arsenic mobility of the tested samples increased in the following order: ASL>RASL>PFA>M1>HPFA>M2.     

某矿业企业遗留重金属污染场地污染调查与风险评估

以某矿业企业搬迁遗留场地为研究区域,根据《场地环境调查技术导则》(HJ 25.1-2014)、《污染场地风险评估技术导则》(HJ 25.3-2014)、《土壤环境质量建设用地土壤污染风险管控标准(试行)》(GB 36600-2018)、《重金属污染场地土壤修复标准》(DB43/T 1125-2016)等进行场地环境调查...     

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.