Simultaneous removal of phenanthrene and cadmium from contaminated soils by saponin, a plant-derived biosurfactant

Batch experiments were conducted to evaluate the performance of saponin, a plant-derived biosurfactant, for simultaneously removing phenanthrene and cadmium from the combined contaminated soils. Results showed that phenanthrene was desorbed from the contaminated soils by saponin with the partition of phenanthrene into surfactant micelle, meanwhile cadmium was effectively removed from the contaminated soils by the complexation of cadmium with the external carboxyl groups of saponin micelle. The efficiencies of saponin for the removal of phenanthrene and cadmium from the contaminated soils were greater than that of Triton X100 and citric acid, respectively. At concentration of 3750 mg/L, saponin has a removal rate of 87.7% and 76.2% of cadmium and phenanthrene, respectively, from the combined contaminated soil. The removals of cadmium and phenanthrene from the soils were not obviously constrained each other. Thus, saponin has the potential for the removal of heavy metal and PAHs from the combined contaminated soils.     

Release of hexachlorocyclohexanes from historically and freshly contaminated soils in China: implications for fate and regulation

Hexachlorocyclohexanes (HCHs) were produced and used in large quantity worldwide and are common soil pollutants. In this study, desorption of α-HCH and γ-HCH from two soil samples collected from a historical pesticide plant in Tianjin, China, was examined. As a comparison, desorption of freshly sorbed γ-HCH was examined, using five typical Chinese soils. Strong resistant desorption was observed for both historically contaminated and freshly contaminated soils, and desorption results were well modeled with a biphasic desorption isotherm. The unique thermodynamic characteristics associated with the desorption-resistant fraction indicated that physical constraint within soil organic matrices was likely the predominant mechanism controlling resistant desorption. Resistant desorption could have significant effects on fate and exposure of HCHs in soil environment. More accurate biphasic desorption models that take into account of the resistant desorption can be used to facilitate regulating, management and remediation of HCH-contaminated sites.     

超声强化茶皂素对污染土壤中重金属去除效果的影响

利用超声强化茶皂素修复土壤重金属,研究了淋洗剂浓度、淋洗方式及淋洗时间对土壤中重金属Cu、Zn、Pb和Cd的修复效果及修复前后土壤重金属的形态变化。结果表明：茶皂素对土壤Cu、Zn、Pb和Cd的解吸率随着茶皂素浓度升高而增大,最大解吸率分别为48.60%、35.10%、28.10% 和45.60%。单独采用超声导致低解吸率,而超声辅助振荡能增加重金属的解吸率(26.3%~61.6%)并缩短达到平衡状态的时间。双常数方程和Elovich方程均能较好描述3种淋洗方式下重金属的解吸动力学过程,重金属的解吸过程是非均相扩散。超声辅助作用下可以活化土壤中的重金属,并通过振荡减少重金属的酸提取态和可还原态,从而减少重金属可迁移性和生物可利用性。     

表面活性剂对Cd2+在沉积物上吸附行为的影响

以Cd2+为重金属代表,阴离子表面活性剂十二烷基苯磺酸钠(SDBS)、阳离子表面活性剂氯化十六烷基吡啶(CPC)、非离子表面活性剂辛基酚聚氧乙烯醚(TX-100)为表面活性剂代表,用实验模拟法研究了3种类型的表面活性剂对Cd2+在沉积物上吸附行为的影响.结果表明,不同种类的表面活性剂对Cd2+在沉积物上的吸附影响不同,SDBS对Cd2+的吸附影响可分为2个阶段,当SDBS初始质量浓度从0 mg/L增加到2 600 mg/L,Cd2+的吸附量从1.52 mg/g增至1.88 mg/g,增加了23.7%,随着SDBS初始浓度继续增加,Cd2+的吸附量开始下降,当SDBS初始质量浓度增至16 000 mg/L,Cd2+的吸附量降低至0.34 mg/g;CPC主要通过在溶液中电离出CP+,CP+与Cd2+竞争沉积物表面的吸附位从而抑制Cd2+的吸附,当CPC初始质量浓度从0 mg/L增加至16 000 mg/L,Cd2+的吸附量从1.50 mg/g降低至0.52 mg/g;TX-100能轻微抑制Cd2+在沉积物上的吸附,当TX-100初始质量浓度从0 mg/L增加到16 000 mg/L时,Cd2+吸附量从1.52 mg/g减少至1.35 mg/g.     

Influence of ozonation on extractability of Pb and Zn from contaminated soils

The effect of soil ozonation on Pb and Zn extraction with EDTA, bioavailability (Ruby's Physiologically Based Extraction Test, PBET) and mobility (Toxicity Characteristic Leaching Procedure, TCLP) of Pb was studied on contaminated soils taken from 7 different locations in the Mezica Valley, Slovenia. EDTA extraction (40 mmol kg(-1)) removed from 27.4+/-1.5% to 64.8+/-1.5% of Pb, and from 1.9+/-0.2% to 22.4+/-2.0% of Zn from tested soils, and significantly reduced soil Pb bioavailability (PBET) and mobility (TCLP). Pretreatment of tested soils with ozone before EDTA extraction enhanced EDTA extractability of Pb for 11.0 to 28.9%, but had no effect on the extractability of Zn. In most of the soils, ozonation had no statistically significant effect on bioavailability and mobility of Pb, residual after EDTA extraction. Using linear regression analysis we found a significant increase (p<0.01) in EDTA extractability of Pb after soil ozonation in soils with a higher initial Pb content. EDTA extractability of Pb after soil ozonation was also significantly higher for soils with a lower Pb extractability when treated with EDTA alone. We found no correlation between soil organic matter content and the percentage of the Pb fraction bound to soil organic matter (where from 25.6+/-1.3% to 73.2+/-0.6% of Pb reside in tested soils) and Pb extractability with EDTA after soil ozonation.     

Potential of different species for use in removal of DDT from the contaminated soils

Dichlorodiphenyltrichloroethane (DDT) and its main metabolites, p,p'-DDD and p,p'-DDE (DDTs in this study included DDT, DDD and DDE), are frequently detected in agricultural soils even though its usage in agriculture was banned in 1980s or earlier. In this study, eleven plants including eight maize (Zea mays) cultivars and three forage species (alfalfa, ryegrass and teosinte) widely cultivated in China were grown in the soils spiked with DDTs to investigate their potential for removal of DDT from the contaminated soils. The plants varied largely in their ability to accumulate and translocate DDTs, with the bioconcentration factor (BCF; DDT concentration ratio of the plant tissues to the soils) ranging from 0.014 to 0.25 and the translocation factor (TF; DDT concentration ratio of the shoots to the roots) varying from 0.35 (Zea mays cv Chaotian-23) to 0.76 (Zea mays spp. mexicana). The amount of DDT phytoextraction ranged from 3.89mug (ryegrass) to 27.0mug (teosinte) and accounted for <0.1% of the total initial DDTs spiked in the soils. After 70d, the removal rates reached 47.1-70.3% of the total initial DDTs spiked in the soils with plants while that was only 15.4% in the soils without plant. Moreover, the higher removal rates of DDTs occurred at the first 20d of experiment, and then the removal rate decreased with time. The highest amount of DDTs phytoextracted was observed in teosinte, followed by Zea mays spp. mexicana, but the highest removal rate of DDTs was found in maize (Zea mays cv Jinhai-6). Even though phytoextraction is not the main removal process for DDTs, the plant species especially Zea mays cv Jinhai-6 showed high potential for removing DDTs from the contaminated soils.     

A multi-process phytoremediation system for removal of polycyclic aromatic hydrocarbons from contaminated soils

To improve phytoremediation processes, multiple techniques that comprise different aspects of contaminant removal from soils have been combined. Using creosote as a test contaminant, a multi-process phytoremediation system composed of physical (volatilization), photochemical (photooxidation) and microbial remediation, and phytoremediation (plant-assisted remediation) processes was developed. The techniques applied to realize these processes were land-farming (aeration and light exposure), introduction of contaminant degrading bacteria, plant growth promoting rhizobacteria (PGPR), and plant growth of contaminant-tolerant tall fescue (Festuca arundinacea). Over a 4-month period, the average efficiency of removal of 16 priority PAHs by the multi-process remediation system was twice that of land-farming, 50% more than bioremediation alone, and 45% more than phytoremediation by itself. Importantly, the multi-process system was capable of removing most of the highly hydrophobic, soil-bound PAHs from soil. The key elements for successful phytoremediation were the use of plant species that have the ability to proliferate in the presence of high levels of contaminants and strains of PGPR that increase plant tolerance to contaminants and accelerate plant growth in heavily contaminated soils. The synergistic use of these approaches resulted in rapid and massive biomass accumulation of plant tissue in contaminated soil, putatively providing more active metabolic processes, leading to more rapid and more complete removal of PAHs.     

Chelating agent-assisted electrokinetic removal of cadmium, lead and copper from contaminated soils

An integrated experimental program was conducted to remove Cd, Pb and Cu from contaminated soil. The chelate agents nitrilotriacetic acid (NTA), diethylenetriamine pentaacetic acid (DTPA) and ethyleneglycol tetraacetic acid (EGTA) were used as washing solutions under different pH conditions and concentrations. Results showed that the extraction efficiency for Cd in decreasing order was NTA > EGTA > DTPA, while for Pb and Cu it was DTPA > NTA > EGTA. The use of higher chelate concentrations did not necessarily result in greater extraction efficiency. Electrokinetic remediation was applied by conditioning anolyte-catholyte pH to neutral values in order to avoid any potential alterations to the physicochemical soil properties. The removal efficiency for Cd was 65-95%, for Cu 15-60%, but for Pb was less than 20%. The phytotoxicity of the treated soil showed that the soil samples from the anode section were less phytotoxic than the untreated soil, but the phytotoxicity was increased in the samples from the cathode section.     

A comparison of the efficiency of different surfactants for removal of crude oil from contaminated soils

This paper presents the results from study investigating the efficiency with which different surfactants remove crude oil from contaminated soil using a soil washing process. The surfactants studied were aqueous solutions of rhamnolipid, saponin and sodium dodecyl sulfate (SDS). The efficiency of surfactants' removal was quantified and then GC/MS analysis conducted to investigate the distribution of hydrocarbons remaining on the washed soil samples compared to those on a control. The results showed that SDS removed the most crude oil from soil, followed by rhamnolipid and then saponin. However, the different surfactants showed preferences in terms of which crude oil components they removed from the contaminated soil. SDS removed more of the aliphatics than aromatic hydrocarbons whereas saponin removed the aromatic hydrocarbon preferentially to the aliphatic hydrocarbons. Clearly these results provide important information for the selection of surfactants used to remove crude oil from contaminated soils.     

生物与化学表面活性剂协同洗脱土壤中PCBs的研究

通过序批实验和土柱淋洗实验研究了由生物表面活性剂鼠李糖脂(RL)与非离子化学表面活性剂十二烷基醇聚氧乙烯(6)醚(POE(6))混合得到的复配试剂洗脱污染土壤中多氯联苯(PCBs)的作用效果及其作用机理。结果表明,同一土样中,从批实验得到的PCBs洗脱率略高于土柱淋洗实验。RL与POE(6)两种单一试剂对人工污染土样中的PCBs洗脱率均大于60%,而对陈化土样中的洗脱率均不到20%,且土壤中的TOC含量越高,PCBs的洗脱率越低。在质量浓度为301 mg/L(10 CMC)及1 505 mg/L(50 CMC)的RL-POE(6)复配试剂中,RL与POE(6)对人工污染土壤中PCBs的洗脱具有一定的协同作用。当复配试剂的浓度为301 mg/L时,RL与POE(6)对陈化土样中PCBs的洗脱没有协同作用;但当RL-POE(6)的浓度增加到1 505 mg/L时,RL与POE(6)对陈化土样中PCBs的洗脱具有明显的协同作用。     

Influence of rate-limited sorption on the cleanup of layered soils by vapor extraction

The conditions under which rate-limited sorption is important for cleanup of layered soils by vapor extraction are investigated. The investigation includes two steps: (a) the cleanup time is estimated for a number of scenario cases by means of a numerical model and (b) the numerical results are approximated using analytical solutions derived for simplified models. In this way, equations are derived, which give insight into the influence of different parameters characterizing the properties of the soil, the geometry of the formation, the mass transfer mechanisms in it, and the distribution of the contaminant mass in the different phases (gas phase, water phase and solid phase). The numerical model used is based on the advection-dispersion differential equations for Darcian isothermal airflow, local equilibrium contaminant mass transfer between gas phase and soil water and first-order kinetics for mass transfer between soil water and solid phase. The numerical results are approximated combining an analytical solution to estimate cleanup time in layered formations for local equilibrium sorption, which has been presented in a previous work (J. Contam. Hydrol., 36 (1999) 105). with an analytical solution based on the well-mixed reservoir model under consideration of rate-limited sorption. The analytical approximation of the cleanup time is in reasonable agreement with the numerical results and allows its estimation with small computational effort.     

曝气生物滤池去除有机物及硝化氨氮的影响因素研究

采用以陶粒为填料的曝气生物滤池(BAF)处理低浓度生活污水,研究在气水比一定的条件下,水力负荷、有机负荷及氨氮负荷对BAF去除有机物及硝化氨氮的性能的影响.研究结果表明,当试验进水COD为105.8～156.6 mg/L,气水比为3:1的条件下,降解有机物的最佳水力负荷为1.35～1.68 m3/(m2·h),COD平均去除率为86.3%.氨氮负荷是影响反应器硝化性能的直接因素.当水力负荷为1.05 m3/(m2·h),平均进水COD为106.1 mg/L时,若使出水氨氮低于15 mg/L,则反应器能承受的最大进水氨氮负荷为0.5 kg/(m3·d)左右.并确立了相应的反应器动力学模型.     

Influence of soil and hydrocarbon properties on the solvent extraction of high-concentration weathered petroleum from contaminated soils

Petroleum ether was used to extract petroleum hydrocarbons from soils collected from six oil fields with different history of exploratory and contamination. It was capable of fast removing 76–94 % of the total petroleum hydrocarbons including 25 alkanes (C₁₁–C₃₅) and 16 US EPA priority polycyclic aromatic hydrocarbons from soils at room temperature. The partial least squares analysis indicated that the solvent extraction efficiencies were positively correlated with soil organic matter, cation exchange capacity, moisture, pH, and sand content of soils, while negative effects were observed in the properties reflecting the molecular size (e.g., molecular weight and number of carbon atoms) and hydrophobicity (e.g., water solubility, octanol–water partition coefficient, soil organic carbon partition coefficient) of hydrocarbons. The high concentration of weathered crude oil at the order of 10⁵ mg kg^?1 in this study was demonstrated adverse for solvent extraction by providing an obvious nonaqueous phase liquid phase for hydrocarbon sinking and increasing the sequestration of soluble hydrocarbons in the insoluble oil fractions during weathering. A full picture of the mass distribution and transport mechanism of petroleum contaminants in soils will ultimately require a variety of studies to gain insights into the dynamic interactions between environmental indicator hydrocarbons and their host oil matrix.     

氮磷比对石油污染沙滩中PAHs去除的影响

溢油风化后粘附在沙滩上,其中的多环芳烃(PAHs)很容易在环境中残留,对人类健康和生态环境构成威胁。以萘、蒽、芘为对象,研究了生物柴油-营养盐联合修复油污沙滩时氮磷比的影响。结果表明,生物柴油可使细沙中的PAHs释放并使其在海水中的浓度显著升高;系统中石油降解菌和异养菌总数分别在N/P为5∶1和10∶1时达最高;在萘的生物降解过程中,N/P为5∶1时的速率常数分别是N/P为10∶1和1∶1时的1.3和2.9倍,蒽的生物降解结果与此类似。然而,不同的N/P比对芘的降解速率几乎没有影响。研究结果可为石油污染沙滩中PAHs的去除提供数据支持。     

Influence of solution acidity and CaCl2 concentration on the removal of heavy metals from metal-contaminated rice soils

Soil washing is considered a useful technique for remediating metal-contaminated soils. This study examined the release edges of Cd, Zn, Ni, Cr, Cu or Pb in two contaminated rice soils from central Taiwan. The concentrations exceeding the trigger levels established by the regulatory agency of Taiwan were Cu, Zn, Ni and Cr for the Ho-Mei soil and Pb for the Nan-Tou soil. Successive extractions with HCl ranging from 0 to 0.2 M showed increased release of the heavy metals with declining pH, and the threshold pH value below which a sharp increase in the releases of the heavy metals was highest for Cd, Zn, and Ni (pH 4.6 to 4.9), intermediate for Pb and Cu (3.1 to 3.8) and lowest for Fe (2.1), Al (2.2) and Cr (1.7) for the soils. The low response slope of Ni and Cr particularly for the rice soils make soil washing with the acid up to the highest concentration used ineffective to reduce their concentrations to below trigger levels. Although soil washing with 0.1 M HCl was moderately effective in reducing Cu, Pb, Zn and Cd, which brought pH of the soils to 1.1+/-0.1 (S.D.), the concurrent release of large quantities of Fe and Al make this remediation technique undesirable for the rice soils containing high clay. Successive washings with 0.01 M HCl could be considered an alternative as the dissolution of Fe and Al was minimal, and between 46 to 64% of Cd, Zn, and Cu for the Ho-Mei soil and 45% of Pb in the Na-Tou soil were extracted after four successive extractions with this dilute acid solution. The efficacy of Cd extraction improved if CaCl2 was added to the acid solution. The correlation analysis revealed that Cr extracted was highly correlated (P < 0.001) with Fe extracted, whereas the Cu, Ni, Zn, Cd or Pb extracted was better correlated (P < 0.001) with Al than with Fe extracted. It is possible that the past seasonal soil flooding and drainage in the soils for rice production was conducive to incorporating Cr within the structure of Fe oxide, thereby making them extremely insoluble even in 0.2 M HCl solution. The formation of solid solution of Ni with Al oxide was also possible, making it far less extractable than Cd, Zn, Cu, or Pb with the acid concentrations used.     

Influence of modified soils on the removal of diesel fuel oil from water and the growth of oil degradation micro-organism

Three soils were modified with two kinds of cationic surfactants in order to increase their sorptive capabilities for organic contaminants. Sorption of diesel fuel oil in water by these modified soils had been investigated. Modified soils can effectively sorb diesel fuel oil from water. The sorption capability of modified soils is: HDTMA-black soil > HDTMA-yellow brown soil > HDTMA-red soil > TMA-black soil > TMA-yellow brown soil > TMA-red soil. Sorption of diesel fuel oil by natural soils and HDTMA modified soils is via partition, the sorption isotherms can be expressed by Henry equation, and logK(SOM) is 2.42-2.80, logK(HDTMA) is 3.37-3.60. Sorption isotherms of TMA modified soils can be expressed by Langmuir equation, the saturation sorption capacities are 1150 (TMA-black soil), 750 (TMA-yellow-brown soil), 171 mg/kg (TMA-red soil), respectively. A diesel fuel oil degradation micro-organism (Pseudomonas sp.) was isolated in the lab. To test the influence of the modified soils on the micro-organism, various growth curves of Pseudomonas in different conditions were drawn. Pseudomonas can grow very well with natural soils and TMA modified soils. The acclimation period of Pseudomonas is reduced. As to HDTMA modified soils, HDTMA loading amount is very important. When HDTMA loading amount is no higher than 0.5 CEC, the micro-organism can grow very well after a long acclimation period.     

几种典型土壤对电动修复镉污染效果的影响

选择5种典型土壤进行了镉污染的电动修复研究。结果表明,经12 d电动修复后,黑土、潮土、红壤、水稻土和黄棕壤中镉的去除率依次为16.7%、21.0%、47.1%、10.7%和12.6%。红壤靠阳极附近Cd含量由初期435 mg·kg-1降至32.4 mg·kg-1,迁移率高达92.5%。黑土、红壤和潮土都维持了较高的电流强度和电渗流量,但由于红壤对碱的缓冲能力较强,修复效果最好。水稻土中电渗流量高,但由于电流低,镉的去除率不高,说明电动修复中电迁移作用强于电渗析。修复后,土壤中可交换态镉、碳酸盐结合态镉、铁锰氧化物结合态镉总量减少,残渣态镉总量增加,有机结合态在阳极附近总量减少、阴极附近总量增加。上述结论揭示了电动修复的土壤镉污染的主要机制,通过镉的运动轨迹和形态分布,可预测不同土壤的电动修复效果,同时能改变不同土壤的电动修复策略,为场地修复提供参考。     

施加电压对铬污染土壤电动修复的影响

试验研究了不同电压条件下电动修复去除效率和单位能耗随施加电压的变化关系,探讨了电动修复经济有效的电压范围.试验选用重铬酸钾作为污染物,配制高岭土中Cr(Ⅵ)初始质量分数为100 mg/kg和500 mg/kg,含水量为50%,试验运行48 h,用乙酸控制阴极pH在4～7之间,施加一系列不同直流电压.试验结果表明,随着施加电压升高,去除效率增大,电压升高到1 V/cm时,去除效率显著升高,2种试验土壤去除效率分别为76.7%和89.8%;同时随着施加电压增加,电能消耗显著增加,与电压呈现线性递增和幂指数递增关系;综合去除效率和单位能耗2种因素,对于试验所研究的土壤,1～1.5 V/cm的电压是较为经济有效的.     

Influence of humic fractions on retention of isoproturon residues in two Moroccan soils

The influence of different fractions of soil organic matter on the retention of the herbicide isoproturon (IPU) has been evaluated. Water and methanol extractable residues of ¹⁴C labeled isoproturon have been determined in two Moroccan soils by β -counting–liquid chromatography. The quantification of bound residues in soil and in different fractions of soil humic substances has been performed using pyrolysis/scintillation-detected gas-chromatography. Microbial mineralization of the herbicide and soil organic matter has been also monitored. Retention of isoproturon residues after 30-days incubation ranged from 22% to 32% (non-extractable fraction). The radioactivity extracted in an aqueous environment was from 20% to 33% of the amount used for the treatment; meanwhile, methanol was able to extract another 48%. Both soils showed quantities of bound residues into the humin fraction higher than humic and fulvic acids. The total amount of residues retained into the organic matter of the soils was about 65 % of non-extractable fraction, and this percentage did not change with incubation time; on the contrary, the sorption rate of the retention reaction is mostly influenced by the clay fraction and organic content of the soil. Only a little part of the herbicide was mineralized during the experimental time.     

Effects of lipids on the sorption of hydrophobic organic compounds on geosorbents: a case study using phenanthrene

The impact of the lipid fraction of natural geosorbents on the sorption of a polycyclic aromatic hydrocarbon was assessed using several experiments. In the first set of experiments phenanthrene was sorbed on a coastal sediment as well as on its humin and humic acid fractions before and after lipid extraction. Before lipid extraction, sorption shows dominantly partitioning characteristics. However, the extraction of lipids from sediment and humin drastically increases, by up to one order of magnitude, their sorption affinity for phenanthrene at low sorbate concentrations, resulting in increased isotherm nonlinearity. This effect is less pronounced for humic acids. One mechanism proposed for the increasing sorption is that lipids, despite their very low relative abundance in the sediments, can compete with phenanthrene for specific high affinity sorption sites (e.g., matrix pores and adsorption sites). This competition is not surprising considering the similar hydrophobic nature of lipids and phenanthrene. Lipids, or any non-polar molecules, could also act like plasticizers by swelling rigid domains and disrupting high affinity sites. In both cases, the removal of lipids (and extraction solvents) makes those sites available for phenanthrene. These provide alternative explanations to the previously proposed “solvent conditioning effect” believed to occur when geosorbents are treated with non-polar solvents modifying the matrix structure, an effect yet to be proven at molecular scale. To further investigate the impact of lipids on sorption, other independent experiments were performed. In a second experiment, re-addition of lipids to the extracted sediment restored the sorption isotherm linearity observed in the native material supporting the absence of irreversible extraction artifacts. However, high addition of lipids (i.e., after saturation of high affinity sites) seems to also enlarge the low affinity partitioning domain. These results are consistent with dual-mode, hole-filling, sorption models involving diffusion. In the final set of experiments, solid-state ¹⁹F-NMR using F-labeled lipids sorbed onto the sediments confirmed that lipids may be in different domains (mobile or rigid) that interact or not with phenanthrene. The possible effects of lipid removal on sorption have been overlooked and should be considered when geosorbents are pretreated.