Improvement in electrokinetic remediation of Pb-contaminated soil near lead acid battery factory

To improve the conventional electrokinetic remediation of Pb-contaminated soil,the Pb-contaminated soil near a lead acid battery factory in the Pearl River Delta region of China was electrokinetically remedied with polarity exchange technique.The variations in Pb removal efficiency and the soil p H value with the treatment time and the exchange polarity interval were determined.It is found that the removal efficiency of Pb reaches a maximum of 87.7% when the voltage gradient is 1 V/cm and the exchange polarity interval is 48 h.This value is far higher than that obtained with conventional electrokinetic remediation（61.8%）.Additionally,the ＂focusing effect＂ which appears in the conventional electrokinetic remediation can be avoided,and thus additional chemicals are not needed for the polarity exchange technique.The mechanism of Pb electromigration behavior in soil during the treatment with the polarity exchange technique was described.

Study on Electrokinetic Remediation of Cadmium-contaminated Soil

In order to improve electrokinetic remediation efficiency of cadmium-contaminated soil,the effects of electric field intensity,remediation time and electrolyte on removal rate of total Cd in Cd-contaminated soil by electrokinetic remediation were studied through the preparation of Cd-contaminated soil and the construction of electrokinetic remediation equipment. The results showed that under the same condition,with the electric field intensity increasing from 2. 5 to 3 V/cm,the total Cd removal rate increased by 10. 62%,and with the increase of the electric field intensity from 3 to 3. 5 V/cm,the removal rate increased by 1. 87%;when the remediation time was prolonged from 72 to 96 h,the removal rate of total Cd increased by 6. 68%,and with the remediation time prolonged from 96 to120 h,the removal rate of total Cd increased by 8. 75%; and with the remediation time prolonged from 120 to 144 h,the removal rate of total Cd only increased by1. 07%. Compared with citric acid as the electrolyte,the acetic acid group improved the remediation efficiency by 12. 14% and the total energy consumption by62. 13%,while the hydrochloric acid group improved the remediation efficiency by 18. 04% and the total energy consumption by 187. 9%. Comprehensively from total Cd removal rate and energy consumption,the remediation effect was the best under the electric field intensity of 3 V/cm and the electrokinetic time of 120 h with acetic acid as the electrolyte,which achieved a total Cd removal rate of 41. 95%.

Study on electrokinetic remediation of cadmium contaminated soils

Kaolinite from a lead-zinc mining district,which was spiked with cadmium,has been treated by electrokinetics to investigate effects of treatment time and applied voltage gradient.The results showed that the increased test duration had induced a higher removal rate of cadmium.Being treated for 7 days,cadmium was removed from kaolinite dramatically.It was also found that higher removal rate happened when a higher voltage gradient was applied and cadmium accumulated near the cathode because pH increased.Increase of pH near the cathode caused accumulation of cadmium.Moreover,it was observed that cation exchange membrane which was placed between kaolinite and cathode could make pH lower than the initial value and avoid the higher pH near the cathode.As a result,the high concentration accumulation of cadmium near the cathode was avoided.

Application of Bioleaching and Electrokinetic Remediation Technology in the Removal of Heavy Metals from Municipal Sludge

Two combinations of bioleaching and electrokinetic remediation were used to remove copper(Cu)and zinc(Zn)from municipal sludge.The results show that bioleaching and electrokinetic remediation technology could remove copper and zinc from the sludge effectively.After performing bioleaching first and then electrokinetic remediation,the concentration of Cu and Zn in the solid phase of the sludge was 63.5 and 50 mg/kg;the concentration of Cu and Zn in the liquid phase was 3 and 30 mg/kg.After bioleaching and electrokinetic remediation were conducted simultaneously,the ferrous ions added in the early electrokinetic process migrated to the cathode zone,so that bioleaching energy was insufficient in the later stage to affect the conversion of heavy metals bound to sulfides,and the concentration of Cu and Zn in the solid and liquid phase of sludge was relatively high.After bioleaching and electrokinetic remediation,sulfide bound Cu was converted into residual Cu and carbonate bound Cu,while carbonate and sulfide bound Zn were converted into residual Zn in the solid phase.

Performance of Metal and Acid Ions Remediation in Contaminated Soils by Electrokinetics with Chitosan Permeable Reactive Barrier

Metal and acid ions contamination of soil in China is serious. To find an efficient solution for remediating the combined pollution,electrokinetics( EK) coupled with chitosan( CTS)permeable reactive barrier( EK/CPRB) was used to investigate the performances of metal and acid ions remediation. Adsorption characteristics of Zn^(2+),Fe^(3+),Ca^(2+),SO_4^(2-) and NO_3^- onto CTS were also conducted. The results showed the sorption of Zn^(2+),Fe^(3+),Ca^(2+),SO_4^(2-) and NO_3^- on CTS could be well described by Freundlich model. When the CTS dosage is 8 g,the total removal efficiency for Zn^(2+),Fe^(3+),Ca^(2+),SO_4^(2-) and NO_3^- is 86. 8%,90. 2%,92. 4%,90. 0% and 82. 5%,respectively. CTS enhanced ions remediation efficiencies significantly compared with the single EK system,especially for SO_4^(2-) and NO_3^-. The results indicate EK/CPRB system is suitable for the remediation of soil contaminated by both metal ions and acid ions.

Remediation of in-situ Leach Mining Contaminated Soil by Amendment-plant Synergism

This study aimed to remediate in-situ leach mining contaminated soil by amendment-plant synergism. The results showed that plant species exhibited ex-tremely significant effects on the concentration of nitrate nitrogen; to be specific, the concentration of nitrate nitrogen in soil planted with wheat was reduced from 692.19 mg/kg to lower than 100 mg/kg; when the mass ratio of amendment to soil reached 3：50 and the amendment particle size was 1-2 mm, the concentration of nitrate ni-trogen in soil planted with wheat was reduced to 43 mg/kg. The amendment type exhibited extremely significant effects on the concentration of ammonium nitrogen; to be specific, when the mass ratio of amendment to soil reached 10：50, the concen-tration of ammonium nitrogen in soil added with 2-3 mm zeolite was reduced from 23 593.75 to 3 300 mg/kg on day 15. Amendments and plants mainly exhibited desorption performance for sulfate radical in soil, and the amendment type extreme-ly significantly affected the concentration of sulfate radical; to be specific, the con-centration of sulfate radical in soil added with limestone increased from 370 mg/kg to 900 mg/kg on day 7.

Application research of enhanced in-situ micro-ecological remediation of petroleum contaminated soil

Experimental study of enhanced in-situ micro-ecological remediation of petroleum contaminated loess soil was carried out in Zhongyuan oil production areas, and the enhanced in-situ micro-ecological remediation technique includes optimistic in-situ microbial communities, physical chemistry methods, alfalfa planting and regulation of soil environmental elements. Experiments showed that the oil content in the contaminated soil with oil content about 2 898.25 mg/kg can be reduced about 98.61% after in-situ micro-ecological remediation for 99 days, which demonstrated the effectiveness of in-situ micro-ecological remediation methods for petroleum contaminated soil in central plains of China, and explored the practical and feasible application of these methods.

Mathematical Modei of In-situ Ozonation for the Remediation of 2-Chlorophenol Contaminated Soil

A microscopic diffusion-reaction modei was developed to simulate in-situ ozonation for the remediation of contaminated soil, i.e., to predict the temporal and spatial distribution of target contaminant in the subsurface. The sequential strategy was employed to obtain the numerical solution of the modei using finite difference method. A non-uniform grid of discretization points was emploved to increase the accuracy of the numerical solution by means of coordinate transformation. One-dimensional column tests were conducted to verify the modei. The column was packed with simulated soils that were spiked with 2-chlorophenol. Ozone gas passed through the column at a flow rate of 100ml·min-1. The residual 2-chlorophenol content at different depths of the column was determined at fixed time intervals. Compared the experimental data with the simulated values, it was found that the mathematical modei fitted data well during most time of the experiment.

In-situ remediation of deep petroleum-contaminated soil injection

A computational fluid dynamics(CFD)numerical simulation and field experiment were used to investigate optimal operating parameters of high-pressure jet grouting equipment and clarify the boundary law of the injection area in the remediation process.The response surface optimization design results show that the optimal injection pressure is 30 MPa,rotation speed is 23 r/min,commission speed is 30 cm/min,and the optimal injection diameter is 147.3 cm.Based on the CFD numerical simulation,the ratio of the injection core,turbulent zone,and seepage zone is approximately 1∶4∶2.The distribution law of jet core,turbulence zone and seepage zone at different cross-sections under 30 MPa operating conditions is as follows:The jet core radius is approximately 100 mm,the turbulence zone is mainly distributed at 100 to 500 mm,the seepage zone is mainly distributed at 500 to 700 mm,the seepage zone could be completed within 2 h,and the proportion of the three boundary zones in the injection zone is similar to that of the numerical simulation.This study provides theoretical parameters and practical reference for the remediation of deep pollution via in-situ chemical oxidation in the Loess Plateau soil environment.

Electrochemical remediation of copper contaminated kaolinite by conditioning anolyte and catholyte pH simultaneously

This report examined electrochemical remediation of copper contaminated kaolinite by controlling electrolytes′ pH for both of anolyte and catholyte simultaneously. Results showed that electrokinetic process and remediation efficiency varied obviously when different buffer systems, including citric acid (test 1), nitric acid + EDTA (test 2) and nitric acid (test 3), were used to control catholyte pH and Na_2CO_3 was used at the same time to control all anolyte one. It was found that under such pH condition soil′s pH in soil column kept at 3.0—7.0 successfully, and correspondingly no copper precipitation and decrease of soil electroconductivity appeared, which are usually observed in electrokinetic process due to OH - introduction into soil column by electrochemical reaction occurred in cathode. Electroosmosis flow rates were almost equal for these three tests, indicating that these buffers did not affect Zeta-potential of kaolinite within the examined duration. More acid and basic solution was added into electrokinetic cell when nitric acid was used as buffer than when nitric acid + EDTA and then citric acid were used. Due to introduction of large amounts of ions into soil column, significant higher current was observed for test 3 than other two. Analysis of copper speciation and total quantity in kaolinite indicated that 22.5%, 23.74% and 55.65% Cu were removed from kaolinite for test 1, test 2 and test 3 respectively after only 10 days′ electrokinetic remediation.

Electrokinetic removal of chromium and copper from contaminated soils by lactic acid enhancement in the catholyte

The electrokinetic removal of chromium and copper from contaminated soils by adding lactic acid in cathode chamber as an enhancing reagent was evaluated. Two sets of duplicate experiments with chromium contaminated kaolinite and with a silty soil sampled from a superfund site in California of USA and polluted by Cr and Cu, were carried out in a constant current mode. Changes of soil water content and soil pH before and after the electrokinetic experiments, and variations of voltage drop and electroosmosis flow during the treatments were examined. The results indicated that Cr, spiked as Cr(Ⅵ) in the kaolinite, was accumulated mainly in the anode chamber, and some of Cr and metal hydroxides precipitated in the soil sections in contact with the cathode, which significantly increased electrical energy consumption. Treatment of the soil collected from the site showed accumulation of large amounts of Cr and Cu in the anode chamber while none was detected in the cathode one. The results suggested that the two metals either complexed with the injected lactic acid at the cathode or existed as negatively charged complex, and electromigrated toward the anode under a voltage gradient.

Electrokinetic movement of multiple chlorobenzenes in contaminated soils in the presence of β-cyclodextrin

This study investigated the electrokinetic （EK） behavior of multiple chlorobenzenes, including 1,2,3,4-tetrachlorobenzene （TeCB）, 1,2,4,5-tetrachlorobenzene （i-TeCB）, and 1,2,3-trichlorobenzene （TCB） in contaminated clayed soils. The effect of β-cyclodextrin （β- CD） on the EK removal of the chlorobenzenes was studied. The largest removal was obtained when Na2CO3/NaHCO3 buffer was used as anodic purging solution without β-CD. The removal efficiencies were related to the aqueous solubilities of chlorobenzenes. With the same cumulative electroosmotic flow, greater solubility led to higher removal efficiency. The addition of β-CD inhibited the EK removal efficiency of all chlorobenzenes. The inhibition increased with the increase of β-CD concentration. With the same β-CD concentration, the inhibition increased with the rise of electric potential. It was found that the inclusion compounds between β-CD and chlorobenzenzes were less soluble than chlorobenzenes. The formation of the less soluble inclusion compounds reduced the aqueous solubility of chlorobenzenes and led to the partial immobilization of the chlorobenzenes that desorbed from soil. It was feasible to use the EK technology to remove chlorobenzenes in contaminated soils using water as the anodic flushing solution. The addition of β-CD was not recommended for the EK removal of chlorobenzenes.

Advances in Microbial Fuel Cells in the Field of Environmental Remediation

In order to protect ecological environment,it is urgent to restore the polluted environment. Among traditional methods of environmental remediation,it is common to add excessive electron donors or electron acceptors to the polluted environment,but these methods have a high cost and can cause secondary pollution easily. Microbial fuel cells( MFCs) can realize the transformation of pollutants and collection of electric energy by using microorganisms as a catalyst; they are clean,efficient and controlled easily and have a wide range of application,so MFCs have wide application prospects in the field of environmental remediation. In this study,MFCs and their applications in the field of environmental remediation were summarized.

Sorption, Desorption, Remediation and Fertility Characteristics of a Clay Soil

This study is conducted to investigate sorption and desorption characteristics of a clay soil of Medicine Hat, Alberta, Canada. Also, the soil fertility after the desorption tests was investigated. Sorption of copper by a clay soil was examined using copper solutions with concentrations from 1,000 mg/L to 5 mg/L. The influence of copper concentration and pH on desorption was also studied. Electrokinetic remediation was carried on soil specimen spiked with copper. Soil fertility parameters for specimens acidized by electrolysis reactions and nitric, hydrochloric, and citric acids were compared. From the results, the adsorption of copper by the soil is proportional to the concentration in the solution and Langmuir isotherm represents the data. Desorption of copper was found to increase with the increase of initial copper in the soil and the decrease ofpH. At pH of 5.75 -4- 0.25, the maximum desorption was 16.5% of initial copper and the minimum was 4.2%. In tests with similar copper concentrations, the maximum desorption was 76.6% in the test with pH of 2. Electrokinetics reduced the pH of soil near the anode to 2.1 and removed 86% of copper. Soil specimen acidized by electrolysis reactions preserved favourable fertility parameters compared with specimens acidized by acids.

生物淋滤电动修复湖泊底泥中的铬

该文采用生物淋滤电动复合技术修复底泥,经生物淋滤后底泥中铬形态发生了改变,可交换离子态、碳酸盐结合态的铬含量比例明显增加,而铁锰氧化物结合态、硫化物及有机结合态以及残渣态的比例含量明显下降(可为电动修复底泥时铬的迁移提供有利条件)。单纯电动修复铬的去除率为32.6%,单纯生物淋滤铬的去除率为25.1%,淋滤去除率与底泥的pH值和氧化还原电位紧密相关。经生物淋滤电动复合处理后,铬的去除总量可达53.4%。生物淋滤电动复合技术对可交换的离子态、碳酸盐结合态、硫化物及有机结合态的铬去除率较高,特别是对碳酸盐结合态的铬去除率达到61.1%。实验表明电动生物淋滤技术具有协同作用,适合湖泊底泥铬污染治理。

极性交换电场辅助植物修复稻田土壤镉污染研究

通过盆栽试验,采用太阳能供电方式,探究在干湿交替的水分条件下,水稻种植过程中极性交换电场辅助植物修复(EKPR)土壤重金属镉(Cd)污染的可行性。控制灌溉条件下,两电极板附近的土壤区域种植水稻作物,中间土壤区域种植水葱作富集植物。结果表明,交换电极使电解水反应产生的氢离子(H~+)和氢氧根离子(OH~-)不断被中和,有效避免了土壤pH值极化。土壤电流变化范围为0.08~0.36 A,说明极性交换和较高的土壤含水率有效确保土壤中的可迁移离子数量和离子流动性,能够驱动重金属迁移。与对照处理(CK)相比,EKPR处理水葱根部干物质量显著增加34.93%;水稻根部和稻谷干物质量显著降低17.21%~30.16%、16.18%~22.28%,叶片和茎部干物质量分别提高3.82%~13.17%、7.59%~30.91%。EKPR处理水葱根部、地上部Cd含量分别提高15.49%~22.45%、33.30%~35.45%;水稻根部、稻谷Cd含量分别降低14.48%~35.06%、39.04%~57.43%。极性交换电场辅助植物修复技术可提高水葱对Cd的富集量,同时降低水稻对Cd的富集量,与CK处理相比,EKPR处理水葱Cd生物富集量显著增加46.48%,水稻Cd生物富集量显著降低24.75%。试验结束后,水稻根系附近的土壤Cd含量下降16.33%~19.14%。研究结果表明,在控制灌溉水稻种植过程中,极性交换电场辅助植物修复是一种可行的修复手段,在作物生产过程中利用电动修复和植物修复实现土壤净化,具有良好的应用前景和现实意义。

植物-电动耦合修复重金属污染土的效能及其强化机制

重金属污染土壤的净化效果直接影响修复后土体的再利用。以Cd、Cu、Ni、Zn、Pb污染土壤为研究对象,采用改进环绕式电极布置,以植物-电动耦合修复下土壤的净化度及土壤性质为重点,厘清关键因素,揭示耦合强化修复机制。结果表明:植物-电动耦合修复下不同重金属的去除率均较单一修复有所提高,重金属赋存形态及植物对重金属的响应是影响修复效果的关键因素。改进环绕式电场的施加能积极调动更大范围土壤中的重金属向植物根系迁移聚集,解决了植物修复中重金属可及性和生物活性低的问题;植物修复的协助有利于改善电动修复对土壤性质的不利影响,解决聚焦效应和高能耗问题。植物-电动耦合修复联合了重金属的空间分布改善、重金属生物利用度提升、植物生长代谢强化及土壤微生物生命活动调节等作用机制,有效提高了重金属污染土壤的净化度,修复后土体可维持稳定的pH值(6.27~7.91)、电导率(108~159μs/cm)及低能耗(13.76~18.81 kW·h/m3),有助于推进污染土壤的可持续利用。

铬污染土壤的电动修复研究

通过调控电动修复阴极pH值及添加增强剂,提升电动修复技术对Cr污染土壤的总Cr去除率,并探究了电动修复工程的能耗变化及Cr迁移分布规律。结果表明,乙二胺四乙酸(EDTA)、柠檬酸和盐酸等增强试剂能显著提升电动修复过程的总Cr去除率。不调控电动修复阴极pH值,电动修复土壤7d,向土壤分别添加EDTA、柠檬酸时,总Cr去除率分别为24.47%、23.24%;不调控阴极pH值,会发生较明显的偏极效应。控制电动修复阴极pH值,电动修复土壤7d,向土壤分别添加盐酸、柠檬酸时,总Cr去除率分别为44.20%(是空白电动修复组的4.9倍)、36.80%;控制阴极pH值,能有效阻止阴极区域Cr发生沉淀作用,提高Cr的去除率;控制阴极pH值不会显著增加电动修复过程能耗。该方法大幅提升了电动修复对土壤中总Cr的去除率,对重金属污染土壤的修复具有指导意义。

生物可降解螯合剂GLDA强化电动治理镉铅砷复合污染土壤研究

以镉铅砷复合污染土壤为研究对象,将生物可降解络合剂谷氨酸二乙酸四钠[tetrasodium N, N-bis(carboxymethyl)glutamic acid, GLDA]应用于电动治理技术,同时结合投加方式和阴极pH值控制技术,以研究电动治理对土壤中不同重金属的同步去除效率并探讨其去除机制。结果显示:(1)GLDA明显提高了土壤溶液中重金属的质量浓度,有利于土壤重金属在电场作用下移出土体;(2)阳极投加GLDA有利于As的去除,土壤As总去除率可达60.7%,但土壤环境过碱时不利于Cd和Pb的移除;(3)阴极投加GLDA结合pH值控制处理中Cd和Pb的总去除率分别可达35.9%和23.7%,在所有处理中最高,且As的去除率(42.3%)也仅低于阳极投加GLDA处理,是一种较优的同步去除Cd、Pb和As的方法;(4)电动处理后土壤pH值和电导率依处理不同会发生较大变化,总体趋势为阳极附近土壤pH值低于阴极附近,且土壤电导率普遍升高。研究结果为GLDA在重金属复合污染土壤电动治理中的应用提供了理论基础和技术支持。

原位电动修复氯离子污染土壤及地下水现场中试研究

针对高浓度氯离子污染地块,开展原位电动修复技术中试研究。在电压梯度为1 V/cm,阴、阳极电解液pH值分别为10,3的条件下通电修复49 d,总耗电量为19385 kW·h,折合单位能耗为48.5 kW·h/m^(3)。中试区域内地下水中氯化物平均去除率达42.5%;土壤中氯离子平均去除率达37.5%,1.5,2.5 m深度土壤中氯离子平均去除率分别为45.4%,23.4%,上层去除率高于下层。原位电动修复技术实现了污染土壤及地下水的同步修复,且并未带入新的化学物质,避免造成二次污染,是一种高效低耗、环境友好的修复技术,具有广阔的应用前景。