Electro ultrasonic remediation of polycyclic aromatic hydrocarbons from contaminated soil

The polycyclic aromatic hydrocarbons (PAHs) with high molecular mass are renown for their high persistence in the soil, hydrophobic and toxicity. Remediation of these pollutants is still an unsolved task and needs more researches to be performed. The coupling of electrokinetics (EK) with ultrasonic energy (US) has advantages on desorbing and migrating PAHs from contaminated soil. US and EK work together to destroy PAHs. The objective of this study was to treat PAHs contaminated soil by using EK and ultrasonication. The contaminated oil contained about 100 mg kg⁻¹ chrysene. Experiments with US, EK and combined EK and ultrasound were conducted in reactors and pans with and without iron anodes. Results indicated that the removal was more effective with lower concentrations of chrysene. The average removal was better in experiment with combined EK and ultrasound using iron anode. This might be due to increase in electroconductivity by iron ions.     

Pulsed electrokinetic removal of Cd and Zn from fine-grained soil

Pulsed electrokinetics studies were carried out to optimize the removal of Zn and Cd from fine-grained soils and to observe the effects of varying the pulse frequency, pulse time ratio (on/off), and DC voltage gradient. Existing forms of heavy metals in the soil matrix were determined using a sequential extraction method. The strongly bound fraction (bound to organic matter and residuals) that is difficult to remove from the soil matrix comprised 74 and 62% of the total Zn and Cd, respectively. In the electrokinetic remediation experiments, MgSO₄ was employed to increase the ionic strength of the soil for 2 weeks. Transportation of heavy metals was influenced by the frequency, pulse ratio, and the voltage gradient of the pulsed electric field. Extraction efficiency of Zn and Cd near the anode was correlated positively with the voltage gradient at a given pulse and ratio. A high pulse frequency (1,800 cycles/h) enhanced the removal efficiency of the heavy metals compared to a low pulse frequency (1,200 cycles/h) at a supplied voltage gradient of 1 V/cm. Although pulsed electrokinetics was more effective in extracting and desorbing ions near the anode than conventional electrokinetics, its ability to transport heavy metals from the anode to the cathode was relatively small. Total removals with pulsed electrokinetics were 21–31% for Zn and 18–24% for Cd. In summary, pulsed electrokinetics can enhance removal efficiency of heavy metals and is beneficial with regard to electrical energy consumption.     

Integrated electrokinetic-soil flushing to remove mixed organic and metal contaminants

The integrated use of hydraulic flushing and electrokinetic treatment was investigated for the remediation of silty sand contaminated by both PAHs and heavy metals. The soil was collected from a polluted former manufactured gas plant (MGP). Four bench-scale experiments were conducted to analyze the ability of the combined hydraulic flushing and the electrokinetic treatment for the simultaneous removal of PAHs and heavy metals. Sequential flushing with ethylenediaminetetraacetic acid (EDTA) or Igepal CA-720 were tested with or without the simultaneous application of a low intensity direct electric field (1 VDC cm⁻¹). The best results were obtained with 0.2 M EDTA flushing in two stages (without and with voltage gradient, 1 VDC cm⁻¹), followed by 5% Igepal flushing in two stages (without and with 1 VDC cm⁻¹). Heavy metals were removed mainly during the EDTA flushing, with removal efficiencies of about 60% for Zn, 80% for Pb, and 30% for Cu. During Igepal flushing, no heavy metals were removed, but PAHs were removed, including 40% phenanthrene, 30% pyrene, and 20% benzo[a]pyrene. Overall, this study showed that a carefully designed sequential hydraulic flushing scheme with selected chelant and surfactant is needed for the removal of both heavy metals and PAHs from MGP silty sands. Combining electrokinetics with hydraulic flushing may not necessarily improve contaminant removal from such soils.     

EK/Fe0-PRB联合修复实际砷污染土壤的协同机制

以我国某矿区砷污染土壤为研究对象,采用EK/Fe⁰-PRB联合修复工艺去除土壤中的砷,考察了土壤含水率及增强试剂对砷去除的影响,分析了修复前后土壤中砷的迁移分布及砷价态分布变化,并借助X射线光电子能谱（XPS）对修复前后PRB填料Fe⁰进行了表征分析,探讨了EK/PRB修复砷污染的协同机制。结果表明,在EK/PRB联合修复过程中,EK去除作用所占比例为22%～43%,而PRB的去除作用所占比例为52%～71%,以PRB的去除作用为主;未添加增强试剂时,阳极液砷收集含量明显高于阴极液砷收集含量,电动去除机制主要为电迁移作用,添加增强试剂后,阴极液砷收集含量所占比例明显升高;EK/PRB修复后,As（Ⅴ）和As（Ⅲ）在土壤、电极液、PRB中的含量比例基本没有变化,As（Ⅴ）含量比例略微升高,即处理之后土壤中的五价砷并不会经氧化还原作用而转变成毒性较高的三价砷;反应后Fe⁰表面存在As（Ⅲ）和As（Ⅴ）,未发现As（0）的存在,因此砷在PRB中仅通过铁表面氧化物的吸附作用而去除。     

Electrokinetic restoration of saline agricultural lands

Salinization of greenhouse soils has become a serious problem in Korea because of the extensive use of chemical fertilizers to improve crop yield. This study investigated the feasibility of electrokinetic (EK) treatment for reclamation of saline soil. Experiments were conducted using voltage gradients of 1, 2, and 3 V/cm applied for 48 and 96 h. Anions such as chloride, sulfate, and nitrate were transported toward the anode and accumulated there, whereas cations were transferred toward the cathode by electromigration. Among the various ions, the highest removal efficiency was achieved for nitrate: >80% at 48 h and >99% at 96 h. Chloride removal after 96 h was substantially higher than that after 48 h because the longer period of time allowed more electrical transport via electromigration and electro-osmosis. However, the removal efficiency for sulfate and calcium did not change significantly between 48 and 96 h. Soil EC was lower than the initial value in all soil sections at 96 h. The lowest value, 1.8 dS/m, was seen in the experiment employing a gradient of 3 V/cm for 48 h. This study demonstrated that nitrate can be readily removed from soil by electromigration. Further, other ions can also be removed by EK treatment; therefore, it could be successfully used for reclamation of saline soils.     

The efficacy of using electrokinetic transport in highly-contaminated offshore sediments

Contaminated offshore mud samples from two regions of Abu Dhabi were tested for selected element removal using electrokinetics. The efficacy of the test results were compared for low and high salinity pore fluids applied to the mud samples. All samples showed some degree of removal efficiency at the anode end of each specimen by 24-h duration tests. The significance of the work was that similar removal efficiencies of about 20 ± 10% were achieved in both the low and high salinity specimens of these heavily contaminated offshore muds, revealing the potential of electrokinetic treatment in marine environments. The electroosmotic efficiency, as measured by the cumulative volume of flow per Coulombs of charge, was 0.002 cm³/C for the low salinity and 0.006 cm³/C for the high salinity samples. These values compared well with the electroosmotic efficiency of 0.008 cm³/C reported for a synthetic soil reference matrix of high electrolyte content. The low electroosmotic efficiency showed that although flow was achieved in all specimens, the mass transport was mainly dominated by electromigration as expected, and not by electrosmosis.     

Removal of Heavy Metals from a Chelated Solution with Electrolytic Foam Separation

Abstract

An experimental study was conducted on the chelation and electrolytic foam separation of trace amounts of copper, nickel, zinc, and cadmium from a synthetic chelated metal wastewater. Sodium ethylenediaminetetraacetate (EDTA), citrate, sodium diethyldithiocarbamate (NDDTC), and potassium ethyl xanthate (KEtX) were used with sodium dodecylsulfate (NaDS) as a foam-producing agent. Experimental results from an electrolytic foam separation process showed that chelating agents NDDTC and KEtX, due to their higher chelating strength and hydrophobic property, can efficiently separate Cu and Ni from chelated compounds (Cu, Ni/EDTA, and Cu, Ni/citrate). In a Cu-EDTA-NDDTC system with a chelating agent/metal ratio of 4, the residual Cu(II) concentration is 0.7 mg/L. The effects of chelating agent types and different chelating agents concentrations on the removal of metal ions were studied. The effect of NaDS dosage on flotation behavior and the efficiency of metal removal were also investigated.     

Step-Wise Extraction of Metals from Dredged Marine Sediments

In this study, step-wise extraction using various extracting agents was carried out in order to enhance the removal of metals from contaminated dredged marine sediment. Five-times repeated extraction using HCl could extract approximately 23% of the As from the sediment, while NaOH extracted 14% of the As with a single extraction. An alternate application of EDTA and HCl extracted 17%, 34%, 9%, 87%, and 41% of the Cd, Cu, Ni, Pb, and Zn, respectively. Step-wise extraction reduced the risk index (RI) of heavy metals to 49% compared with untreated sediments, which were caused mainly from the decrease in the Cd concentration after chemical extraction in sediment.     

电场和提取剂对提取胞外聚合物的影响

本文研究了电场和提取剂对胞外聚合物提取效果的影响,实验测定了在交流电场下不同的提取剂如：NaOH、EDTA、Tris和硫酸对提取液中的多糖含量,结果表明,电场和提取剂对提取效果有明显影响。     

Synthesis of Novel Magnesium-Doped Hydroxyapatite/Chitosan Nanomaterial and Mechanisms for Enhanced Stabilization of Heavy Metals in Soil

A novel magnesium-doped hydroxyapatite/chitosan nanomaterial (MHAP@CS) was prepared as soil passivator for treatment of copper and cadmium contaminated soil. The mechanism of the immobilization performance improvement was proposed. According to the characterization, magnesium ions were successfully incorporated into hydroxyapatite (HAP), and chitosan (CS) was also supported on HAP. Toxicity characteristic leaching procedure (TCLP) and Tessier sequential extraction method were conducted to evaluate the immobilization efficiency of MHAP@CS, and MHAP@CS showed higher efficiency in the reduction of the mobility of Cu and Cd than HAP. Meanwhile, adsorption experiments and XPS characterization were used to investigate the passivation mechanism. The maximum removal amount of MHAP@CS for Cu(II) and Cd(II) was 133.49 mg g^?1 and 131.84 mg g^?1 respectively. According to XPS and Zeta potential, the stabilization of Cu(II) and Cd(II) by MHAP@CS involved ion exchange, electrostatic adsorption and surface complexation. After magnesium doping and CS modification, the electronegativity and ion exchange capacity of HAP were significantly improved. The excellent immobilization performance suggested that MHAP@CS is an effective, green and facile soil passivator.

     

Recycling wasted scallop shell as an adsorbent for the removal of phosphate

Lots of scallop shells were discharged from local restaurants and marine product manufacturers around the city of Gangneung and most of them are dumped into landfill. The scallop shell was recycled as an adsorbent for the removal of phosphate. The shell size greatly affected phosphate removal. One gram of shell having diameter of around 45 μm removed 100 mg/L of phosphate in 3 h while that of 3 mm hardly removed in 80 h. Phosphate removal was not much affected by the pH in the range of 2.0–7.5 but it was scarcely removed beyond pH 8.0. Higher temperature was preferred for phosphate removal but the removal efficiency was almost constant over 35 °C. The maximum phosphate removal capacity was obtained through Langmuir isotherm plotting and it was as high as 23.0 mg-phosphate/g-shell. On the purpose of enhancing the adsorption capacity of scallop shell, it was treated with chemical reagents such as HCl, NaOH, NH₄HCO₃ and EDTA. HCl-treatment increased the adsorption capacity of the shell having diameter of 45 μm by 39.8% than raw scallop shell, but the treatment showed negligible effect on the shell of 1000 μm in diameter. Packed-bed containing HCl-treated scallop shell with 500 μm in diameter removed 20 mg/L of phosphate stably for 15 days and the removal efficiency was over 85% throughout operation.     

Effect of processing fluid and initial concentration on electrokinetic removal of environmental hormone—nonylphenol (NP) from soil matrix

This study was aimed to investigate the electrokinetic removal of environmental hormone––nonylphenol (NP)––from soil matrix under potential gradient of 1 V cm^?1 for 5-day treatment. The EK experiments were conducted with four processing fluids of de-ionized water, citric acid, NaOH, and methanol in a Pyrex glass cylindrical cell. Results showed that the elcetrokinetic removal efficiency of the above-mentioned processing fluid was 29, 36–38, 43–53, and 53–69%, respectively. It was found that the removal of NP in EK system was highly related to the solubility of NP in processing fluid. Approximate 88.8–94.2% of NP removal was collected in the cathode reservoir after EK treatment, which was 7.9–16.2 times greater than that collected in the anode reservoir. It was concluded that NP was mainly removed from anode to cathode by electroosmosis flow. The electrokinetic phenomenon of current density, electroosmistic permeability, and power consumption were also investigated.     

Tetrasodium iminodisuccinate as a biodegradable complexing agent for remediating metal-contaminated soil

Soil washing is a rapid and cost-effective method to treat contaminated soils. However, conventional chelating agents exhibit adverse environmental effects. Tetrasodium iminodisuccinate (IDS) is a new type of amino carboxyl chelating agent, which exhibits strong chelating performance, high solubility in aqueous solution, and is environmentally friendly in soil. In this study, batch washing of Cu, Pb, and Cd removal from simulated contaminated soil and real project-scale soil of a Pb-polluted field was explored to evaluate the application of IDS in the remediation of potentially toxic metal-contaminated soil. The effects of the IDS solution pH, concentration, reaction temperature, liquid/soil (L/S) ratio, number of washing cycles, and contact duration were investigated, and the optimal conditions were identified as follows: pH 7, IDS concentration 10 mmol · L⁻¹, L/S ratio 10:1; 25°C; and 24 h. Almost 80.6% of Cu, 71.1% of Pb, and 59.1% of Cd were removed from simulated contaminated soil under optimal conditions. The primary potentially toxic metal removal mechanisms were analyzed by potentially toxic metal state detection before and after IDS washing. Real project-scale Pb-polluted field washing was demonstrated under the same conditions in addition to the IDS concentration of 4.5 mmol · L⁻¹. The Pb concentration was reduced from 460 to 86.8 mg · kg⁻¹ (mean value), which is below the threshold identified in the ‘Risk Assessment of Soil Environmental Health in Shanghai’ (Residential Area, 140 mg · kg⁻¹). The results confirm that IDS is a promising soil washing agent that can effectively remove potentially toxic metals from contaminated soil and minimize environmental risks.     

Hybrid Technologies for the Remediation of Diesel Fuel Polluted Soil

Diesel fuel may be released into soil due to anthropogenic activities, such as accidental spills or leaks in underground storage tanks or pipelines. Since diesel fuel is mainly composed of hydrophobic organic compounds, it has low water solubility. Therefore, treating contaminated areas with conventional techniques is difficult. In this study, electrokinetic treatment of soil contaminated with diesel fuel was carried out. Two different hybrid approaches to pollutant removal were tested. A surfactant was used as a processing fluid during electrokinetic treatment to increase desorption and the solubility of diesel fuel. Additionally, a hybrid technology combining a Fenton reaction and electrokinetic remediation (EK‐Fenton) was tested in an attempt to generate favorable in situ degradation of pollutants. The efficiency of each treatment was determined based on diesel fuel removal. After 30 days of treatment, the highest removal of diesel fuel was found to be achieved with the EK‐Fenton process.     

Electrokinetic treatment for clayed and sandy soils

Electrokinetic treatment has proven to be an attractive alternative to clean polluted soils. This friendly environmental procedure can be approached by a physicochemical model dealing with the oriented displacement of pollutants by means of the fluid and/or charge flow through a porous media induced by an electric field. Concerning the porous media, soil texture is the main issue to consider, since it is related with physicochemical properties that may define the electrokinetic phenomena. In this paper, two different soil textures were tested under the same experimental conditions. Physicochemical characterization of clayed and sandy unpolluted soils, later mixed with PbCO₃, were done. Zeta potential measurements were performed to approach the soil particles interphase with three aqueous solutions. Clayed and sandy soil, mixed with cerusite, were treated by electrokinetics during 24 h. Results for sandy soil contaminated with Pb, using ammonium acetate and acetic acid as anolyte and catholyte respectively, reported Pb mobility due to a fluid flow from anode to cathode; in accordance with zeta potential indicating more negative values for ammonium acetate solution, compared with EDTA and acetic acid. For the clayed soil, lead mobility was detected, even if no electroosmotic flow appeared. Finally, the same experimental conditions were applied to a real soil containing mining wastes, in this case lead mobility was due to electroosmotic and electromigration flow.     

Development of electrokinetic-flushing technology for the remediation of contaminated soil around nuclear facilities

The effects of a flushing by a pump on an electrokinetic-flushing remediation of contaminated soil were estimated. The soils were sampled from the sites around nuclear facilities which were built on a high hydro-conductivity of sandstone. An electrokinetic-flushing equipment with a pump was manufactured to estimate the effect of a flushing on an electrokinetic-flushing remediation. In order to select an optimal reagent suitable to the characteristics of a soil near nuclear facilities, 4 experiments were executed with 4 candidate reagents selected from 12 reagents and the results of the experiments are as follows. The removal efficiencies of cobalt and cesium from the contaminated soil with the acetic acid were the highest, which were 92.1% and 83.1%, respectively. The effluent solution volume generated from an electrokinetic remediation was very smaller and it was 5% below that from a soil washing. Next, the results from a comparison of an electrokinetic-flushing remediation and an electrokinetic remediation revealed that the removal efficiencies of Co²⁺ and Cs⁺ by an electrokinetic-flushing remediation for 5 days were increased by 25% and 35% when compared to those by the electrokinetic remediation, but the effect of a flushing by the electrokinetic-flushing equipment started to decrease after 5 days. The removal efficiencies of Co²⁺ and Cs⁺ by an electrokinetic-flushing remediation for 15 days were increased by 6.8% and 7.7% when compared to that by an electrokinetic remediation. Namely, the higher the hydro-conductivity of a soil was, the larger the effect of a flushing was on an electrokinetic-flushing remediation.     

Hybrid ceramic membrane microfiltration and electrolysis process for Cu-removal from aqueous solutions

This study aims to fabricate a low-cost ceramic microfiltration membrane by mixing kaolin 4.2 wt%, silica 5.8 wt%, starch 20 wt%, graphite 30 wt%, and sodium silicate 40 wt%. The produced paste was molded into a cylinder (1.0 cm high, 5 cm diameter) and dried in an oven at 90°C for 1 h, and then sintered in a furnace at 650 °C for 2 h. The characterization of the produced ceramic membrane was performed by X-ray diffraction analysis, Fourier transformed infra-red spectroscopy, and scanning electron microscopy. Furthermore, the contact angle of the membrane surface was measured, thus demonstrating that the surface is hydrophilic. The fabricated ceramic membrane was investigated for its chemical resistance in strongly acidic and alkaline media. The mass loss of membrane in HCl solution at pH = 2 for 200 h was not more than 0.18%, while it was 2% in alkaline NaOH solution (pH = 12). The fabricated ceramic membrane was combined with an electrolysis process for applying as a new hybrid process for copper ions removal from an aqueous solution. The effects of three operating parameters of electric voltage, initial pH, and initial copper concentration on the performance of copper removal percentage were investigated. To investigate the independent effect of the hybrid electrolysis process versus microfiltration, two experiments with and without an electric field were conducted in 100 min. The copper concentration was decreased from 350 to 160 ppm only by applying the microfiltration method, whereas hybrid electrolysis and microfiltration decreased the copper concentration from 350 to 10 ppm. The regeneration of the composite membrane was evaluated in four consecutive cycles. The percentage of copper ions removal after 4 cycles without washing is about 97%. The proposed process is effective and fast for copper ions removal from the solution, with an excellent yield of 97.4%.     

Development of pilot-scale electrokinetic remediation technology to remove 60Co and 137Cs from soil

Pilot-scale electrokinetic remediation equipment suitable to the geological characteristics of South Korean nuclear facility sites was developed for the remediation of radioactive soil. The optimal experiment conditions were chosen through pilot-scale electrokinetic remediation experiments, and the experimental results are presented. The removal efficiencies of Co²⁺ and Cs⁺ from artificially contaminated soil after 15 days were 98.4 and 94.9, respectively, and the generated effluent volume was 3.4 ml/g. The removal efficiencies of ⁶⁰Co and ¹³⁷Cs by nitric acid were increased by 3.1% and 2.0% more than those by acetic acid. Moreover, when nitric acid instead of acetic acid was used, it had an advantage of a reducing electricity consumption due to its higher electrolytic conductivity. The higher the radioactivity concentration of the soil was, the more the removal efficiencies of ⁶⁰Co and ¹³⁷Cs were increased. Namely, the removal efficiencies of ⁶⁰Co and ¹³⁷Cs from the soil of high concentrations were increased by 14.4% and 3.8% more than those from the soil of low concentrations. The larger the particle size of the soil was, the more the removal efficiency of ¹³⁷Cs increased. Namely, the removal efficiency of ¹³⁷Cs from the soil of an average 1.4 mm particle size was increased by about 2.3% more than that from the soil of an average 0.7 mm particle size. Also, the removal efficiencies of ⁶⁰Co and ¹³⁷Cs by the application of an electric current of 15 mA/cm² were increased by 1.4% and 4.4% more than those by the application of 10 mA/cm². Therefore, the total removal efficiency of ⁶⁰Co and ¹³⁷Cs from the radioactive soil of about 2000 Bq/kg was 95.8% by an electrokinetic remediation by the application of an electric current of 15 mA/cm² for 55 days.     

Combined ultrasonication and electrokinetic remediation for persistent organic removal from contaminated kaolin

Electrokinetics alone (EK) and ultrasonically enhanced electrokinetics (EK-US) tests were studied to compare and examine the combining effects of these two methods on the removal of the three persistent organic pollutants (POPs): hexachlorobenzene (HCB), phenanthrene (PHE) and fluoranthene (FLU) from kaolin. Two pair tests were conducted into two experiments with different initial low (100 mg/kg) and high (500 mg/kg) contaminant concentrations. Results from the experiments show that, generally, EK-US tests have higher electroosmotic flow, higher current and better performance than EK alone tests. However, ultrasonic enhancement can increase the removal rate only up to about 10% more. Among the three POPs, HCB is the most difficult to treat because of its very stable structure while the other two PAHs are easier to remove.     

Controlled partial neutralization of amphoteric ion exchange resin for improved metals separation

Controlled partial neutralization of an amphoteric aminomethylphosphonium functional ion exchange resin (Lewatit TP-260) was investigated. The particular goal of controlled neutralization was to replace H⁺ in the acidic phosphonium groups with Na⁺ ions but leave the basic amino groups protonated. In this manner, metals’ sorption is enhanced and undesired pH changes during the metal separation process are avoided. The conjugate bases of organic weak acids (sodium formiate, sodium acetate and sodium citrate), sodium phosphate and NaOH were studied as neutralizing agents. The organic acid salts and sodium phosphate were all found to be suitable. Lengthening the neutralization cycle and using more concentrated neutralization agents were found to yield higher extents of neutralization and more uniform profiles along a resin bed. Concentrated NaOH also neutralized the amine group from the resin. With dilute NaOH, desired extent of neutralization was not achieved within a reasonable time. The effect of partial neutralization on metal sorption was tested with dynamic single column experiments. 5.5 BV of Ag–NaCl solution could be purified from Ca, Mg, Pb and Zn when the resin was partially neutralized with 2.0 M NaAc. With the acid form resin, the impurity metals broke through at 1.0 BV.