Application of APG and Calfax 16L-35 on surfactant-enhanced electrokinetic removal of phenanthrene from kaolinite

Removal characteristics of polycyclic aromatic hydrocarbons (PAHs) from low-permeable soil using a surfactant-enhanced electrokinetic (EK) process were investigated. Phenanthrene and kaolinite were selected as a representative PAH and a model soil. A nonionic surfactant, alkyl polyglucosides (APG), and an anionic surfactant, Calfax 16L-35, were used to enhance the solubility of phenanthrene. The two surfactants showed similar solubilization capacities for phenanthrene, while only APG was affected by sorption. When surfactants were applied to EK process, the electrical potential gradient was lower than that of water. The electroosmotic flow (EOF) decreased as the concentration of surfactant increased. In the case of APG, the removal efficiency of phenanthrene increased with the surfactant concentration. The APG micelles containing phenanthrene easily migrated to the cathode reservoir by EOF. On the other hand, Calfax 16L-35 did not enhance the removal efficiency even at the highest concentration, because most of Calfax 16L-35 remained in soil, and only small amount existed in effluent. It was thought that, during electrokinetic process, Calfax 16L-35 was adsorbed onto soil and the migration of the surfactant from cathode to anode was superior to EOF due to anionic charges of Calfax 16L-35. A nonionic surfactant, APG, seems to be suitable for surfactant-enhanced electrokinetic remediation.     

Experimental study of the effect of material and arrangement of electrodes and voltage on the electro-remediation of saturated clays containing chloride and sulfate ions

Electro-remediation process (ERP) is used for dewatering and decontaminating of the soil and improving its mechanical properties. In this study, the effect of voltage, electrode materials, and their arrangement on ERP were studied. The saturated clayey soil was remolded in four boxes at a dry density of 16.2 kN/m³. The process was performed in three stages. The chemical tests at the end of ERP indicated that the absorption of chloride ions in the anode may differ from 89 to 642% due to electro-migration phenomenon. The pH of the soil decreases in anode zone and increases towards the cathode zone. Up to 92% of the sulfate ions were transported and accumulated in the anode. However, in highly contaminated soil, the absorption ratio is 5% in the cathode due to the domination of electro-osmosis process. It was indicated that the electro-osmosis permeability coefficient (K_e) depends on the applied voltage, the soil type, and temperature and its reduction versus time is inversely related to applied voltage. Also, sulfate ions reduced by 74% in the anode due to a change in absorption direction. The results showed that the optimum configuration is linear along with a voltage of 18 V.     

考虑温度电动淋洗法去除污染软土中铬试验研究

针对铬污染软土,自行设计了电动淋洗试验装置,开展了铬污染软土室内土柱淋洗试验,分析了试验过程中电流、电解质溶液pH的变化以及淋洗液种类、外加电压、温度对重金属铬去除特性的影响。结果表明:电动淋洗试验可以有效去除土壤中的重金属铬;相对于单一淋洗试验,用10 V电压强化淋洗试验显著提高了重金属铬去除效果,淋洗液为十二烷基苯磺酸钠（SDS）时Cr（VI）和Cr（总）去除效率是单一淋洗法的2.79,3.12倍。当电压为10 V,温度升高至45 ℃时,淋洗液为柠檬酸（CA）和草酸（OA）的各组试验表明Cr（Ⅵ）与Cr（总）去除率均相应提高;而淋洗液为十二烷基苯磺酸钠时的试验组中Cr（VI）去除率提高了5.84%,Cr（总）去除率降低了4.25%,表明升高温度使部分Cr（VI）还原成不易迁移的Cr（III）;淋洗液为草酸的试验组中升高温度时Cr（Ⅵ）与Cr（总）去除率最高,分别达到了82.08%、77.57%,分别相应提高了27.65%、26.01%。电动淋洗试验后,铬污染软土土粒结构变得更紧密,土粒之间的孔隙减小且被填充的更加密实。     

Electrokinetic remediation of metal contaminated glacial tills

This paper presents the results of an experimental investigation which studied the feasibility of using the electrokinetic process to remediate contaminated clays of glacial origin, otherwise known as glacial tills. An overview of the electrokinetic phenomena, as well as previously performed laboratory and field investigations, is first presented. The methodology of the electrokinetic experiments which were conducted to investigate the removal of metals from a glacial till is then described. A total of 16 experiments were conducted using glacial till samples obtained from a project site near Chicago. Sodium and calcium were used as the surrogate cationic metallic contaminants. These experiments demonstrated that ion transport during the electrokinetic process occurs due to both electro-osmosis and electromigration, but that due to electromigration is significantly higher than that due to electro-osmosis. Unlike other clays such as kaolinite, the glacial till used for this investigation possessed high buffering capacity because of its high carbonate content which prevented the acid front migration from the anode to the cathode during the electrokinetic process. The ion removal efficiency of the electrokinetic process was found to increase when: (1) the voltage gradient applied to the soil was increased, (2) the initial concentration of the contaminants was increased, and (3) the duration of the treatment process was increased. The ion removal efficiency was also greater for smaller ions which possess less ionic charge and when the ions existed independently in the soil as compared to when they coexisted. This investigation suggests that the electrokinetic process has significant potential for remediating glacial tills contaminated with metals. However, the properties of Na and Ca are not representative of contaminants, such as heavy metals, so further investigations are needed.     

三维电极法预处理山梨酸废水

用三维电极法对山梨酸废水进行了降解实验,并考察电极材料、反应器电压、电解时间、进水pH值等因素对处理效果的影响。实验结果表明,以不锈钢作阳极,石墨作阴极,柱状活性炭作填料,在槽电压为20 V、主电极极间距为11 cm的条件下,pH值为 4.0±0.2的山梨酸废水在电解20～30 min后,COD去除率达48%以上,而且废水的BOD/COD提高到0.40。     

古尔班通古特沙漠树枝状沙丘土壤水分时空变异特征

认识沙漠土壤水分的时空变异性,是揭示沙漠生态系统生态-水文格局的基础。利用中子土壤水分仪的实测数据,对古尔班通古特沙漠树枝状沙丘土壤水分时空变异进行了系统分析。研究表明:① 沙丘不同部位土壤水分随时间具有一致性变化规律,上层土壤和下层土壤的变化趋势有所不同。0~1 m土层坡顶>坡中>坡脚,1~2 m土层坡脚>坡中>坡顶。② 土壤水分具有明显的季节变化和分层变化特征。春季是古尔班通古特沙漠土壤水分最丰富、变化最迅速的时期;0~40 cm、40~140 cm、140~200 cm土层土壤水分变异系数分别为13.56%、5.35%和0.80%,与不同土层水分来源和消耗以及植物根系分布相对应;不同土层土壤水分的变异强度要大于不同部位土壤水分的变异强度。③ 植被和地形对土壤水分的空间分异作用明显,沙丘坡脚处以及荒漠灌木梭梭根区始终存在土壤水分相对富集区。     

脉冲电解处理石油废水的实验研究

石油废水中含有多种有机物,成分复杂,其治理是当今急需解决的问题.用自制的反应器以石墨为电极材料,应用脉冲电解方法,进行处理石油废水的实验.实验结果表明:在电解时间 30 min,电解电压 10 V,脉冲电源频率 3 750 Hz,占空比 50 %,pH＝9,电极间距 2.5 cm,电极直径 1.0 cm,电解质浓度 0.2 % 的条件下进行电解,废水的处理效果可达到 89 % 以上.处理后的废水低于国家第二类污染物最高允许排放浓度的二级排放标准.脉冲电解法不但处理含油废水效果显著,而且设备简单,易于操作,为处理石油废水提供了一项新技术.     

青藏高原风火山流域坡面尺度活动层土壤水热时空变化特征

以风火山流域某阴坡坡顶、 坡底和阳坡坡底活动层土壤水热及气象资料为基础, 对青藏高原多年冻土区不同地形条件下的土壤水热时空变化特征进行了分析。结果表明： 在融化阶段, 除表层5 cm外, 阴坡坡底各深度土壤开始融化日期均比坡顶早, 比阳坡坡底晚; 阴坡坡脚各深度土壤含水量均大于坡顶和阳坡坡底。在冻结阶段, 开始冻结日期在阴坡坡底均比坡顶早, 但比阳坡坡底晚; 阴坡坡底各深度土壤含水量均高于坡顶相应土层的含水量, 在20 cm、 100 cm、 160 cm深处高于阳坡相应土层的含水量, 但在5 cm、 50 cm深处, 稳定冻结后两者的含水量差异较小。在整个冻融过程中, 阴坡坡底土壤温度对气温变化的响应弱于坡顶及阳坡坡底, 但其土壤水分对降水的响应强于坡顶及阳坡坡底。植被生长发育受水分和热量条件的制约, 不同地形条件下水热时空变化差异将影响植被空间分布特征。在未来气候变暖情况下, 上坡位植被可能因为水分胁迫而退化, 出现荒漠化现象, 而下坡位由于受侧向流的影响, 土壤水分对降水的响应强烈, 植被不会发生显著退化; 在不同坡向之间, 同一坡位阳坡植被退化程度可能大于阴坡。     

Electrokinetic remediation of an electroplating site: design and scale-up for an in-situ application in the unsaturated zone

In-situ electrokinetic remediation of contaminated soils requires integrated approaches and adequately engineered setups to control relevant mass fluxes. Based on laboratory findings, this study presents the design of a pilot-scale remediation at an operating electroplating site. The fine-textured soil developed from Jurassic limestone exhibits a chromium, copper, nickel, and zinc contamination down to depths of more than 4 m. The feasibility of an electrokinetic remediation in the unsaturated zone was tested in a lab-scale experiment with subsoil material sampled at the site. The electrodes were placed in water-impermeable, ion-selective membrane wells. This construction allows the necessary watering of the electrodes, maintains unsaturated conditions in the soil compartment, and enables the transfer of contaminant ions into the wells. In addition, the soil is protected from pH changes caused by water electrolysis at the electrodes. The setup includes a watering and drainage system to compensate the electroosmotic water flux and impede desiccation of the anodic region. With a direct current of 70 V and an electric field strength of 2.2 V cm⁻¹, contaminant removal rates amounted up to 27% and 66% (w/w) of the initial zinc/copper and chromium/nickel concentrations. Copper, nickel, and zinc accumulated in the cathode well, while chromate species were enriched in the anode well. Given the successful lab-scale remediation, the pilot plant was designed for the in-situ treatment of a soil volume of 12 m³ below a production hall. A power of 500 V DC at a maximum current of 30 A is supplied by a transformer rectifier. This yields an electric field strength comparable to the lab-scale experiment and thereby similar contaminant transport velocities. A vacuum distillation unit is employed for process water reuse and to control electrolyte conductivity. To cope with chlorine gas generation at the anodes a gas absorber unit is employed. According to the lab-scale results, about 2, 9, 9, and 15 kg zinc, chromium, copper, and nickel, respectively, are expected to be removed from the field plot during an operation time of 10 months.     

Electrokinetic remediation of perchloroethylene-contaminated soil

One large group of persistent and toxic contaminants is the hydrophobic organic contaminants. Among them, perchloroethylene (PCE) has been recognized as a representative group of these pollutants with low solubility. This study reports on the effects of electrokinetic remediation with non-ionic surfactant on PCE-contaminated soil. The performance of electrokinetic process was investigated in the treatment of clay soil that artificially contaminated with two levels: 10,000 and 30,000 mg/kg PCE and 0.33 g/kg Triton X-100. A DC power supply with electric voltage (1 V/cm) was used for 8–16 days. A negatively charged soil surface resulted in a more negative zeta potential and greater electroosmotic flow toward the cathode. The PCE was measured after extraction using n-hexane and analyzed by Fourier transform infrared spectroscopy instrument. The water content of soil was kept 25 % (w/w). Results were shown that PCE removal efficiency achieved was 74 and 89 % for 10,000 and 30,000 mg/kg PCE, respectively, for 16 days. Therefore, in this study, the integration of electrokinetic with non-ionic surfactant as a hybrid method was most effective for the remediation of PCE-contaminated soils.     

小降雨事件对土壤水分及植物水势空间差异性的影响

本文以云南省蒙自市断陷盆地高原面上典型封闭式岩溶洼地小流域为研究对象,研究小降雨事件对土壤水分及植物水势的影响。结果表明:（1）在研究区内小降雨事件一般只能补给10 cm以上的土壤,因此在旱季（强降雨事件发生前）,土壤水分随着深度的增加整体呈变小的趋势;受洼地地形影响,整个土壤剖面（0 ~ 80 cm）的土壤水分存在从坡顶到洼地底部逐渐增加,苹果树叶水势逐渐升高的现象;受地质背景的影响,土石质坡地平均土壤水分比石质坡地土壤水分高2.67%,相对应的土石质坡地苹果树受干旱胁迫的程度要低于石质坡地。（2）通过观测对比发现,8天内12次的小降雨事件可以使0~10 cm土壤水分整体上略有升高,但并未能完全改变0~10 cm土壤水分洼地底部大于两侧坡地,而土石质坡地高于石质坡地的特征。（3）小降雨事件虽然只能补给0~10 cm的土壤水分,但由于坡地地区苹果树根系分布较浅（5~30 cm）,部分浅层分布的苹果树根系已能吸收到水分,另一方面小降雨事件具有降温、增湿,减少太阳辐射的作用,可以减小苹果树蒸腾作用,从而降低苹果树叶水势,因此推测小雨事件可以明显减轻苹果树受干旱胁迫的程度      

An experimental study on the remediation of phenanthrene in soil using ultrasound and soil washing

A series of laboratory experiments were carried out in this study to investigate the remediation of phenanthrene contaminated soil using ultrasound and soil washing. The results indicated that ultrasound and soil washing could significantly enhance the remediation efficiency of each other. The performance of the combined ultrasonic and soil washing process was then investigated, and the impacts of four experimental variables including the initial concentration of phenanthrene in soil, sonication time, pH of washing solution, and washing flow rate were examined using an orthogonal experimental design method. The analysis of variance (ANOVA) of experimental results revealed that the initial phenanthrene concentration, sonication time and soil washing flow rate showed significant effects (P ≤ 0.05) on the remediation efficiency. A pseudo-first-order kinetics model was developed for describing the remediation process, and a maximum remediation efficiency of 69.5% was observed in the study after 20 min of treatment under the experimental conditions. Therefore, the results indicate that the combined ultrasonic and soil washing process could represent a promising technology for the effective remediation of phenanthrene contaminated soil.     

低电压偶极地电提取装置在广西昭平古袍金矿区试验效果

通过在广西昭平古袍金矿区已知矿体上方进行的低电压偶极地电提取装置地电提取试验研究,显示阴极提取和阳极提取在已知矿体上方都获取到了清晰的地电提取异常。在矿头位置,阳极提取量比阴极提取量要大,而在矿体隐伏端,阴极的异常特别明显。阳极与阴极提取量之间几乎没有相关性。将阴离子与阳离子累加能更加清晰地指示出矿体的位置。说明地电提取测量法在广西大瑶山古袍金矿区寻找隐伏金矿是可行的,并且用偶极地电提取装置寻找隐伏金矿效果会更好。     

Removal of fluorine from contaminated field soil by anolyte enhanced electrokinetic remediation

Feasibility of electrolyte conditioning with strong alkaline solution on electrokinetic remediation of fluorine-contaminated field soil was investigated in the laboratory. The initial concentration of fluorine, pH and organic matter content in the soil were 1,058 mg kg⁻¹, 8.17 and 20.51 g kg⁻¹, respectively. Electrokinetic experiments were conducted under two different concentrations of alkaline solution and three different voltage gradients. The removal of fluorine increased with the concentration of the alkaline solution and applied voltage and fluorine removed up to 73% within 10 days. Anolyte enhanced electrokinetic process could promote effectively the migration of fluoride in soil. The electromigration was the main transport mechanism and the electroosmotic flow had an effect on the migration of fluoride in soil. Appropriate anolyte enhanced electrokinetic method could be applied to remediate fluorine from contaminated field soil and has significant potential for removing other anionic pollutants such as arsenate and chromate from soil.     

冻融试验对土中含水量分布的影响

The silty clay and silty loam are two typical soil types obtained from two test sites along the Qinghai-Tibet railway. The two types of soil have been designed various initial dry densities, water eontents, temperature conditions in repeated freezing and thawing tests with free access to water at the bottom. Afterfreeze-thaw cycles, the moisture content in the freeze-thaw zone increases more than that in the unfrozen zone to the peak approximately at the top of the samples. With comparison of the water contents in the frozen and thawed states, the moisture content in the upper freeze-thaw zone in the frozen state is greater than that in the thawed state, while that in unfrozen zone in the frozen state is smaller than that in the thawed state. Within the region of the frost front, the water content in frozen state is smaller than that in thawed state. These findings help to study the freeze-thaw mechanisms deeply and perfect the forecasting module of moisture transferring in freeze-thaw cycles.     

黄土高原退耕坡地土壤水分空间变异性研究

以神木生态观测站为例,利用经典统计学方法对黄土高原退耕坡地土壤水分在空间三维不同方向和不同位置的空间变异性进行了研究,并对空间变异的尺度和时间依赖性等问题进行了探讨,以便为坡地水分管理和植被恢复提供参考。研究结果表明土壤水分在垂直方向和水平方向(垂直于坡长方向)的平均变异程度为弱变异;而在东西方向(坡长方向)、二维平面和三维空间上为中等变异性;土壤水分沿坡长方向从坡顶到坡脚表现出先减小后增大的趋势,且在各坡位变异程度不一,呈现出变异程度为坡上>坡中>坡下的趋势;土壤水分沿南北方向表现为阴坡>山脊>阳坡的明显趋势,其变异程度为阳坡>阴坡;在40~200 cm土层深度内,土壤水分在垂直方向表现出先减小后增大的趋势,且在各土层的变异程度与各层平均土壤水分成明显的正相关。     

地裂缝与斜交地铁隧道动力相互作用试验研究

通过进行地裂缝与斜交地铁隧道的物理模型试验,研究地铁列车荷载作用下地裂缝与斜交马蹄形地铁隧道的动力相互作用特性。试验结果表明:地铁行驶产生的振动在土层中各个方向传播时会有不同程度的衰减,地裂缝对地铁振动具有阻隔作用;地裂缝附近隧道下方土层的振动要比上部土层强烈;地铁隧道的拱底部位相比拱腰和拱顶部位振动响应更强烈。地裂缝未活动时,隧道底部与土体的接触附加压力较大;地裂缝上盘下降时,位于地裂缝附近的下盘隧道底部和上盘隧道顶部与土体的接触附加压力较大。地裂缝未活动时,激振作用产生的隧道顶部和底部的附加应变均较小;地裂缝上盘下降后,位于上盘的隧道顶部和位于下盘的隧道底部产生负的附加应变,位于下盘的隧道顶部和位于上盘的隧道底部产生正的附加应变,且随上盘下降量的增大,附加应变逐渐变大。     

Sulphate reducing bacteria to precipitate mercury after electrokinetic soil remediation

Combined treatment with electroremediation and sulphate reducing bacteria (SRB) was tested in laboratory and pilot scale. The contaminated soil came from a chlor-alkali factory and contained about 100 mg/kg Hg. Iodide/iodine complexing agent was used to mobilize mercury. Mercury iodide complexes were moved to the anode solution using an electric field. The anode solution was then mixed with hydrogen sulphide (H₂S) containing water, causing precipitation of mercury sulphide. The H²S was produced at site by a SRB reactor. Precipitation problems arising from the nature of the anode solution were expected, since this solution is highly acidic, very oxidised and may contain iodide/iodine that strongly complexes mercury and can hinder mercury sulphide precipitation. Mercury concentrations in the anode solution were up to 65.7 mg/L (field) and 15.4 mg/L (lab. scale). Reduction of mercury in the water was >93% at all times. Iodide did not hinder the process: Nonetheless, in the lab system, iodide concentration was high in the anode solution but mercury reduction was> 99.9%. The redox potential was sufficiently low for HgS precipitation during the experiments, except for a short period, when the mercury removal decreased to 94%. Sulphate reducing bacteria are shown as a viable tool for the treatment of mercury contaminated, acidic, oxidative, iodide containing water, such as that produced by electrokinetic remediation. A second SRB step or other water treatment is required to reduce the mercury concentration to environmentally acceptable levels. Redox potential is the most sensitive factor in the system.     

Removal of Cr from synthetic wastewater by sorption into volcanic ash soil

The possibility of using volcanic ash soils (VAS) or Andisols as a low-cost and natural adsorbent is investigated in this study for the removal of Cr (VI) from synthetic wastewater. Andisols can be used as adsorbent because they are characterized by the presence of non-crystalline secondary minerals such as allophane and imogolite that show variable charge characteristics and have the ability to retain cations and anions. The adsorption of Cr on to two VAS from Mt. Isarog and Mandalagan (B-Horizon), Philippines, was carried out at ambient temperature using batch adsorption studies. The effects of different parameters such as amount of adsorbent, contact time, initial Cr concentration and pH of the solution were investigated. The results showed that the VAS from Isarog is more effective in the removal of Cr than in Mandalagan. The maximum removal efficiency of the Isarog soil for a Cr concentration of 10mg/L reached 89% with a dose of 20 g/L at a moderately acidic pH of 3. The Mandalagan soil on the other hand could remove only 65% at the same pH conditions and parameters. The difference in the removal of the two soils may be attributed to their physico-chemical properties in which the Isarog soil has higher clay content, porosity and lower bulk density. Isarog soil has fine particles with higher surface area and more active non-crystalline minerals and thus has higher removal efficiency than Mandalagan soil. Based on the results, the use of VAS from Isarog appears to be economical and an alternative to commercially available adsorbents for the removal of Cr from contaminated wastewater.     

电渗前后淤泥质土的物理力学性质对比研究

为深入研究电渗排水对土体工程性质的影响,采用铁丝为电极,在模型箱内对南京市某河道淤泥质土进行电渗排水 模拟试验。电渗前后土的物理力学性质对比分析表明：电渗后土体的液、塑限与塑性指数均降低;电渗前后土体在相同含 水量和干密度情况下进行直接剪切试验,发现电渗后土体的凝聚力和内摩擦角均降低,即电渗后土体在特定情况下出现了 强度衰减的现象。论文基于土中阳离子流失机理对土体在特定情况下的强度衰减现象进行了微观解释。另外,利用提出的 新的电渗机理从微观角度解释了电渗过程中土体开裂现象,阳极因快速失水,最早出现裂隙,但裂隙延展范围较小;阴极 含水量始终高于阳极,且失水速度较慢,裂隙延展范围较大。值得一提的是,在以往的研究中并未关注到电渗加固过程中 土中阳离子流失对电渗后土体性质的影响。