In Situ Electrokinetic Removal of Salts from Greenhouse Soil Using Iron Electrode

An electrokinetic (EK) field study was performed on a pilot scale (2.2 × 3.3 × 0.3 m³, W × L × D) in a greenhouse by using Fe electrodes and bentonite backfill. When a constant voltage gradient was applied, the current intensity was affected by electrode position, and the soil temperature increased with the current intensity. After the EK treatment, the soil pH was little changed and the cations were hardly removed because of the ion exchange in the bentonite. However, the anions were mostly removed by electromigration, resulting in the reduction of the soil electrical conductivity. The field study demonstrated that in situ EK process is feasible for the remediation of greenhouse soils. In addition, the improvement of EK system and the role of bentonite backfill were discussed.     

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.     

Removal of phosphate from agricultural soil by electrokinetic remediation with iron electrode

Phosphorus is considered the limiting nutrient in eutrophication of agricultural soil in Korea. This study evaluates the coupled application of electrokinetic process by iron and titanium electrodes for removal of phosphate from agricultural soils. Experiments were conducted to evaluate phosphate removal under the following conditions: (I) control; (II) 1% starch addition in the soil without EK; (III) 1% starch addition at the anolyte using a cast iron anode and a carbon cathode; (IV) no starch addition using a cast iron anode and a carbon cathode, and; (V) 1% starch at the anolyte using a titanium anode and a carbon cathode. When an iron anode was used under 0.5, 1.0 and 2.0 V/cm, the removal of phosphate was significant at 2 V/cm. The addition of starch also helps to remove nitrate significantly using an iron electrode. The results reveal that iron electrodes result in significantly more removal compared to titanium electrodes.     

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。     

Stepwise addition of chemical reagents for enhancing electrokinetic removal of cu from real site contaminated soils

In this study, a circulation-enhanced electrokinetics (CEEK) system integrated with the stepwise addition of chemical reagents was used to remediate copper-contaminated soils collected from a real site. At first, an optimal extraction process of different chemical reagents was found to obtain the highest copper removal efficiency by conducting batch extraction experiments. The chemical reagents served as extracts including EDTA, NaOH, and sodium dithionite + sodium citrate. Then, CEEK integrated this optimal extraction, that is, the treatment of 6-day EDTA, NaOH, EDTA, sodium dithionite + sodium citrate, and EDTA in a series. According to experimental results, the NaOH and sodium dithionite + sodium citrate could effectively facilitate the copper removal during the extraction and electrokinetics (EK) processes. The optimal extraction process for this real contaminated soil (94% copper removal efficiency) was the alternative extraction of EDTA, NaOH, and sodium dithionite + sodium citrate. The copper removal efficiency of the real contaminated soil could reach around 55% after 30-day CEEK treatment. The continuous decline of soil copper concentration of this integrated EK technique could be achieved as the remediation time was extended sufficiently.     

Electrode Configuration for Electrokinetic Restoration of Greenhouse Saline Soil

Electrokinetic restoration (EKR) of saline soil has been achieved successfully on a laboratory scale. In this study, the effectiveness of an electrokinetic system with one anode in the center of the electrokinetic cell and two cathodes at the end of the cell was investigated to simulate the EKR system, with electrodes installed in the ridge and furrow pattern of a field. Anions were transported toward the anode centered in the cell, and cations were moved toward both cathodes. Chloride and nitrate were almost completely removed from the soil; however, a certain amount of sulfate accumulated in the anode region. Although the voltage influenced the transport of salts in the soil, there was no significant increase in the reduction of electrical conductivity at a higher voltage gradient. The pattern of salt removal was symmetric around the center anode, and energy consumption was less than that of a normal system. This means that the system can be used effectively to remove salts from saline greenhouse soil.     

Investigation of Selectivity and Kinetic Behavior of Strong‐Base Ion Exchange Resin Purolite A 520E for Nitrate Removal from Aqueous Solution

Abstract

The aim of this work is to present experimental results on the removal of nitrate by nitrate selective ion exchange resin, Purolite A 520E. The resin particle size, nitrate concentration, temperature, and stirring speed were investigated as experimental parameters and the optimum conditions for nitrate removal were determined. Nitrate removal by strong base anion exchange resin Purolite A 520E was carried out with the batch method in the presence of chloride and sulfate ions. The existence of a high concentration of competing ions in a solution resulted in a reduction of nitrate removal. Nitrate removal ratios decreased from 98% to 85% and 88%, respectively, in the presence of chloride and sulfate ions when the chloride and sulfate ratios were increased in solution. The process kinetics were predicted by using Homogenous Diffusion Models. It was seen that about 98% of nitrate in the aqueous solution could be removed using optimum conditions.     

Accelerated removal of nitrate from aqueous solution by utilizing polyacrylic anion exchange resin with magnetic separation performance

In order to quickly remove nitrate from aqueous solution, a magnetic strong base quaternary ammonium anion exchange resin (MAER) has been successfully designed and synthesized. The physicochemical properties of the MAER as well as its adsorption ones for nitrate removal were investigated in detail. A series of batch experiments were carried out to evaluate the effects of several factors on removal efficiency of nitrate, such as retention time, resin amount and initial nitrate concentration. Compared to the commercial Purolite A300 and D213, the equilibrium time for the adsorption process using MAER was only around 20 min, which is significantly less than that of two ones mentioned. Furthermore, the kinetic process of nitrate sorption on MAER could be well described by both pseudo-first-order and pseudo-second-order models. In addition, the results of batch experiments can be better fitted by the Langmuir and Freundlich adsorption isotherm models. Most importantly, the effects of competing ions on nitrate removal followed the order as: SO₄²⁻ > Cl⁻ > HCO₃⁻. These results are of significance in guiding the development of novel resins with the rapid nitrate removal rate from aqueous solution, which would improve efficiency and save energy greatly.     

Removal characteristics of metal cations and their mixtures using micellar-enhanced ultrafiltration

Divalent ions were removed by ultrafiltration of anionic surfactant solution and the removal characteristics in single and mixed systems were investigated. The removal efficiency was >95% when the ratio of sodium dodecyl sulfate (SDS) to metal ions (S/M ratio) was >10. In single metal systems, the removal efficiency of each metal ion was almost the same. In the mixture, however, there was slight difference (ca. 1–2%) of removal efficiency and the order was Cd²⁺>Cu²⁺>Co²⁺≈Zn²⁺. As S/M ratio increased, the difference in removal efficiency diminished. To explain the difference of removal efficiency in a mixture, complexation of divalent metal ion with counterion was considered. The distribution of complexed form of each metal ion was calculated, but it did not coincide with the experimental results. Further research will be necessary for a clear explanation.     

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.     

Influence of anions on Reactive Red 43 removal in electrochemical coagulation process

The electrochemical coagulation technique (EC) and potentiodynamic polarization tests were used to evaluate the influence of some anions as chloride, sulfate and nitrate on the removal of Reactive Red 43 (RR43) as a model pollutant using aluminum and iron anodes. Higher removal efficiency was obtained using aluminum anodes in the presence of chloride ions. Potentiodynamic polarization tests and determination of total Al³⁺ concentration showed that sulfate ions inhibit the release of Al³⁺ from the anode while in the existences of chloride and nitrate current efficiency was higher than 100%. Dye removal efficiency was considerably decreased by increasing the anion concentration and adding sulfate and nitrate to the solution containing chloride. In EC using iron anodes, the higher removal efficiency was achieved in the presence of chloride and sulfate ions. Potentiodynamic polarization tests revealed that the passive layer formation on the iron surface in the solution containing nitrate caused a considerable decrease in the current and removal efficiency. This passive layer was destroyed by adding chloride ions and in this condition, the removal efficiency and quantity of Fe²⁺ ions increased remarkably. According to the results, iron anode was more efficient than aluminum in the removal of RR43.     

Removal of metal ions by ultrafiltration of a micellar solution containing anionic surfactant

Heavy metals in wastewater were removed by ultrafiltration of a micellar solution containing surfactant such as sodium dodecyl sulfate. Experimental results showed that permeate flux was primarily controlled by the operating parameters such as transmembrane pressure difference, flow rate and feed concentration. The average permeate flux increased at a higher transmembrane pressure, feed velocity, and at a lower solution concentration. The transmembrane pressure had a relatively small effect on metal removal whereas the level of surfactant-to-metal ratio (S/M) had a substantial effect. The optimal ratio of S/M for a best removal of metal ions was measured around 5 and 8 in the presence of sodium dodecyl sulfate, and the affinity resulted in the order of Cr> Co> Ni> Mg.     

Behavior of hydrogen nanobubbles in alkaline electrolyzed water and its rinse effect for sulfate ion remained on nickel-plated surface

More than ordinary rinsing using pure water, cathode water obtained by electrolysis of dilute potassium carbonate aqueous solution (alkaline electrolyzed water: AEW) exhibits a stronger rinse effect for elimination of remaining sulfate ions when rinsing nickel-plated surfaces. This rinse effect was recognized even for AEW that was used 24 h after it was produced, but not 1 week after. Behaviors of hydrogen nanobubbles observed by dynamic light scattering revealed nanobubbles of about 128-nm diameter even 24 h after generation. The Ostwald ripening phenomenon was observed. Hydrogen nanobubbles in an open system changed: some shrank because of ripening, later dissolving in the aqueous solution and disappearing; others showed swelling and expansion. One week later, few nanobubbles smaller than 300 nm were observed. Rinse effects by AEW, which are attributable to the actions of hydrogen nanobubbles generated in AEW, occur because sulfate ions are cleaned and removed from the nickel-plated surface.     

Electrochemical removal of sodium ion from fermented food composts

Fermented food composts, to be recycled into fertilizer and animal feed, require sodium chloride concentrations to be less than 1 wt% due to several toxicities. Electrochemical methods are used to remove sodium ions from fermented food composts. By washing the compost with tap water (with no electric current applied), 48% of the initial sodium ion is removed. With an electric current density of 3 mA/cm² (the distance between the electrodes is 16 cm), the removal efficiency increases to 96% for a 36 h operation. Major factors influencing the efficiency are the treatment time and the electric current density. Removal efficiency increases with energy demand to yield 96% removal at 60 Kwh/m². Due to the difference in relative ionic mobility, less than 9% of calcium is removed, during the same operation time, which supports the feasibility of this method.     

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.     

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.     

Removal of radio-tagged protein and stearic acid soil from glass

Both algal protein and stearic acid soils are removed by water alone to near a 50% level; retained soil then becomes more difficult to remove. The bonding of protein soil to glass is stronger than that of tristearin, with indications that stearic acid soil is als slightly more adherent. The shape of the protein soil removal curves lacks the sigmoid shape of the tristearin or stearic acid soils, suggesting either the absence of sharp dependence upon critical micelle concentration, or the existence of adsorption largely at an essentially single energetic level. Both these soils are generally more effectively removed by anionic surfactants than was tristearin. Sodium tripolyphosphate is quite effective for removal of both soils, but combination with surfactants failed to provide the synergistic combinations found in tristearin removal. Nevertheless surfactant soil removal was improved by STP combination.     

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.     

Kinetic,isotherm and thermodynamic study of nitrate adsorption from aqueous solution using modified rice husk

In this article, we prepared anionic sorbent using rice husk (RC). Anionic rice husk (ARC) structural characteristics and adsorption properties for nitrate removal from aqueous solution were investigated. The sorption of NO₃^? by batch method is carried out. The optimum conditions of sorption were found to be: a sorbent dose of 0.4 g in 100 mL of NO₃^? solution, contact time of 90 min, pH = 7. In optimum condition, removal efficiency was 94.3% for the NO₃^?. The nitrate adsorption process was well described by the pseudo-second-order kinetic model, and the experimental isotherm data fitted well with the Langmuir, Freundlich and Dubinin–Radushkevich (D–R) isotherm models. Thermodynamic parameters such as Gibbs free energy change, enthalpy change and entropy change were calculated and the results showed that the adsorption of nitrate on ARC was spontaneous and exothermic in nature. The effect of other anions were also studied and was found that the anions reduced the nitrate adsorption in the order of carbonate > chloride > phosphate > sulphate. ARC was used for the removal of NO₃^? from real wastewater (urban wastewater) that high performance of adsorbent was considerable.