Evaluation of hydrophobicity in PAH-contaminated soils during phytoremediation

The impact of recalcitrant organic compounds on soil hydrophobicity was evaluated in contaminated soil from a manufactured gas plant site following 12 months of phytoremediation. Significant reduction in soil wetting and water retention was observed in contaminated soil compared to an uncontaminated control. Phytoremediation was effective at reducing total PAHs by 69% with corresponding changes in soil classification from extremely hydrophobic (initial sample) to moderately-strongly hydrophobic (planted) and hydrophilic-very hydrophilic (unplanted) after 12 months. The greatest reduction in soil hydrophobicity was observed in the unplanted, unfertilized treatments that had the lowest removal rate of PAHs. The presence of plants may contribute to hydrophobicity in contaminated soil.     

Determination of biodegradation potential by two culture-independent methods in PAH-contaminated soils

Biodegradation potentials of polycyclic aromatic hydrocarbons (PAHs) were determined with soil samples collected from various depths of a PAH-contaminated site and of a site nearby where PAHs were not found. Putative dioxygenase genes were amplified by a primer set specific for initial dioxygenases and identified by web-based database homology search. They were further categorized into several groups of which four dioxygenases were selected as probes for DNA hybridization. The hybridization signals according to the presence of putative dioxygenases were positively related to the extent of PAH contamination. However, the signal intensities varied depending on the probes hybridized and moreover were not consistent with PAH biodegradation activities determined by CO2 evolution. Despite widely accepted advantages of molecular biodegradation assessment, our data clearly present the variations of assessment results depending on the genetic information used and suggest that the methodology may tend to underestimate the real biodegradation capacity of a site probably due to the limited dioxygenase database available at the moment. Therefore, the molecular assessment of biodegradation potential should involve a very careful primer and probe design and an extensive microbiological examination of a site of interest to accurately delineate the biodegradation potential of the site.     

Inclusion of vegetable oils in Fenton's chemistry for remediation of PAH-contaminated soils

Pre-treatment with vegetable oils prior to treatment with Fenton's reagent led to increased oxidation by the latter of polycyclic aromatic hydrocarbons (PAHs) in a pair of model manufactured gas plant soils. This effect was frequently most pronounced in the cases of high-molecular-weight (HMW) PAH species, indicating a preferential "targeting" of oxidative equivalents toward these compounds. In both cases, addition of oils--either corn oil containing unsaturated lipids or palm kernal oil (PKO) comprised primarily of saturated fats--at the 5% dosage was required; supplementation with 1% oil apparently did not sufficiently facilitate PAH desorption and mass-transfer to have a notable effect on degradation efficiency. In PKO-supplemented reactions, replacement of H2O2 with calcium peroxide (CaO2) further increased the extent of PAH removal. Again, this was most pronounced in the cases of several HMW PAHs; among a suite of four 5- and 6-ring PAH (benzo[a]pyrene, dibenz[a, h]anthracene, benzo[g, h, i]perylene and indeno[c, d]pyrene), average removal efficiency increased from 5% in PKO-supplemented reactions in which H2O2 served as the oxidant, compared to 44% in CaO2-containing reactions. This last finding is consistent with other reports which have indicated that slower-release oxidants are better suited to degradation of contaminants which, despite vegetable oil treatment, remain soil-sorbed.     

Modeling in situ ozonation for the remediation of nonvolatile PAH-contaminated unsaturated soils

Mathematical models were developed to investigate the characteristics of gaseous ozone transport under various soil conditions and the feasibility of in situ ozone venting for the remediation of unsaturated soils contaminated with phenanthrene. On the basis of assumptions for the mass transfer and reactions of ozone, three approaches were considered: equilibrium, kinetic, and lump models. Water-saturation-dependent reactions of gaseous ozone with soil organic matter (SOM) and phenanthrene were employed. The models were solved numerically by using the finite-difference method, and the model parameters were determined by using the experimental data of Hsu [The use of gaseous ozone to remediate the organic contaminants in the unsaturated soils, PhD Thesis, Michigan State Univ., East Lansing, MI, 1995]. The transport of gas-phase ozone is significantly retarded by ozone consumption due to reactions with SOM and phenanthrene, in addition to dissolution. An operation time of 156 h was required to completely remove phenanthrene in a 5-m natural soil column. In actual situations, however, the operation time is likely to be longer than the ideal time because of unknown factors including heterogeneity of the porous medium and the distribution of SOM and contaminant. The ozone transport front length was found to be very limited (< 1 m). The sensitivity analysis indicated that SOM is the single most important factor affecting in situ ozonation for the remediation of unsaturated soil contaminated with phenanthrene. Models were found to be insensitive to the reaction mechanisms of phenathrene with either gas-phase ozone or dissolved ozone. More study is required to quantify the effect of OH* formation on the removal of contaminant and on ozone transport in the subsurface.     

Chemical and bioanalytical characterisation of PAHs in risk assessment of remediated PAH-contaminated soils

Polycyclic aromatic hydrocarbons (PAHs) are common contaminants in soil at former industrial areas; and in Sweden, some of the most contaminated sites are being remediated. Generic guideline values for soil use after so-called successful remediation actions of PAH-contaminated soil are based on the 16 EPA priority pollutants, which only constitute a small part of the complex cocktail of toxicants in many contaminated soils. The aim of the study was to elucidate if the actual toxicological risks of soil samples from successful remediation projects could be reflected by chemical determination of these PAHs. We compared chemical analysis (GC-MS) and bioassay analysis (H4IIE-luc) of a number of remediated PAH-contaminated soils. The H4IIE-luc bioassay is an aryl hydrocarbon (Ah) receptor-based assay that detects compounds that activate the Ah receptor, one important mechanism for PAH toxicity. Comparison of the results showed that the bioassay-determined toxicity in the remediated soil samples could only be explained to a minor extent by the concentrations of the 16 priority PAHs. The current risk assessment method for PAH-contaminated soil in use in Sweden along with other countries, based on chemical analysis of selected PAHs, is missing toxicologically relevant PAHs and other similar substances. It is therefore reasonable to include bioassays in risk assessment and in the classification of remediated PAH-contaminated soils. This could minimise environmental and human health risks and enable greater safety in subsequent reuse of remediated soils.     

Algal tests with soil suspensions and elutriates: a comparative evaluation for PAH-contaminated soils

An algal growth inhibition test procedure with soil suspensions is proposed and evaluated for PAH-contaminated soil. The growth rate reduction of the standard freshwater green alga Pseudokirchneriella subcapitata (formerly known as Selenastrum capricornutum) was used as the toxicity endpoint, and was quantified by measuring the fluorescence of solvent-extracted algal pigments. No growth rate reduction was detected for soil contents up to 20 g/l testing five non-contaminated Danish soils. Comparative testing with PAH-contaminated soil elutriates and soil suspensions showed that the suspensions had toxicity endpoints 2.5-3000 times lower than tests with the corresponding elutriates. Algal growth inhibition tests with soil suspensions are recommended for screening purposes as a supplement to elutriate testing. Experiments with a phenanthrene-spiked soil, showed that the sorbed compound did not contribute to the toxicity. However, the soil did act as a reservoir for phenanthrene, allowing desorption to occur continuously during the algal test which maintained higher concentrations of phenanthrene in the dissolved phase. Phenanthrene-spiked soil incubated for 90 days before algal testing, resulted in a reduction of the toxicity to P. subcapitata by a factor of 76 (from EC10 = 0.3 to 23.6 g soil/l). However, during this 90-day period the total concentration of phenanthrene in the soil decreased by 38% (from 322 to 199 mg/kg) indicating that phenanthrene in the aged soil had become less bioavailable.     

Wet air oxidation and catalytic wet air oxidation for dyes degradation

Background, aim, and scope  

Textile industry produces wastewater which contributes to water pollution since it utilizes a lot of chemicals. Preliminary studies show that the wastewater from textile industries contains grease, wax, surfactant, and dyes. The objective of this study was to determine the treatment efficiency of the nickel catalysts supported on hydrotalcites in three-dye model compounds and two types of wastewater.     

粘土矿物修复重金属污染土壤

简要介绍了我国土壤重金属污染的现状与危害.通过粘土矿物在重金属污染土壤中净化功能的阐述,提出利用粘土矿物修复土壤重金属污染的观点.继而从天然和改性粘土矿物特性,叙述了粘土矿物修复土壤重金属污染的机制与应用进展及其影响因素.最后讨论了粘土矿物在修复土壤重金属污染过程中值得注意的几个问题,并展望了粘土矿物在该领域应用中的发展方向.     

Impact of chemical oxidation on soil quality

Oxidation treatment helps to reduce the polycyclic aromatic hydrocarbon (PAH) load in contaminated soils but it may also have an effect on the soil quality. The impact of permanganate and Fenton oxidation on soil quality is investigated. Soil quality is restricted here to the potential for plant growth. Soil samples were collected from an agricultural field (S1) and a former coking plant (S4). Agricultural soil was spiked with phenanthrene (PHE) and pyrene (PYR) at two concentrations (S2: 700 mg PHE kg⁻¹, S3: 700 mg PHE kg⁻¹ and 2100 mg PYR kg⁻¹). Soils were treated with both oxidation processes, and analyzed for PAHs and a set of agronomic parameters. A plant germination and growth test was run with rye-grass on treated soils. Results showed that both treatments produced the expected reduction of PAH concentration (from 64% to 97%). Besides, a significant loss of organic C and N, and strong changes in available nutrients were observed. Permanganate treatment increased the specific surface area and the cation exchange capacity in relation to manganese dioxide precipitation, and produced a rise in pH. Fenton oxidation decreased soil pH and increased the water retention capacity. Plant growth was negatively affected by permanganate, related to lower soil permeability and aeration. Both treatments had an effect on soil properties but Fenton oxidation appeared to be more compatible with revegetation.     

Applicability of the bioluminescence inhibition test in the 96-well microplate format for PAH-solutions and elutriates of PAH-contaminated soils

The use of conventional plastic microplates for a miniaturised luminescent bacteria test may result in an underestimation of the toxicity for poorly water soluble highly adsorbing toxicants such as PAHs. In this study, the suitability of microplates for testing elutriates of PAH-contaminated soils was investigated. The LUMIStox test was performed as the standard test in the miniaturised format using contaminated soil elutriates and aqueous solutions of four selected PAHs (viz. naphthalene (NAP), acenaphthene (ACE), fluorene (FLU), and phenanthrene (PHE)). For the aqueous PAH-solutions, we observed reduced light inhibition values for the miniaturised bioassay when using black microplates made of polypropylene (PP) and polystyrene (PS) compared to the standard LUMIStox test. This phenomenon was most likely due to adsorption of toxicants to the microplate surfaces with PAHs of lower water solubility being significantly more affected; however, after minimizing the exposure of samples to plastic surfaces, polystyrene microplates revealed equivalent performance (>80% 'relative' light inhibition) to the standard glass cuvette test system. For soil elutriates, black microplates again exhibited slightly lower light inhibition values while white plates made of PS and Barex resulted in a pronounced overestimation of toxicity for a coloured soil elutriate. In general, microplates were applicable for testing elutriates of PAH-contaminated soils. In cases where samples are coloured or turbid, the application of black microplates is recommended.     

Fenton氧化技术处理稠油污染土壤

利用Fenton氧化技术对稠油污染土壤进行氧化处理,分析对后续微生物修复的促进作用。向1 000 g石油类含量为8%的稠油污染土壤中加入10.0 mL 18 mmol/L Fe2+溶液与10.0 mL 30%H2O2,反应时间为2 h。氧化处理后土壤中石油烃的总去除率可达到31.38%,胶质去除率为45.22%,沥青质去除率为51.26%,胶质的分子量由1 841下降到1 472,沥青质的分子量由5 831下降到5 073。Fenton氧化可使土壤酶活、各类微生物的数量及呼吸强度有不同程度的下降,但在氧化后30 d内,土壤各类微生物数量都超过了原有水平,其中细菌数量最高达到9.84×105CFU/g,是氧化前的数量的1.57倍。以上实验结果表明,Fenton氧化可以有效去除土壤中胶质和沥青质,并且使土壤中微生物的生长速率加快。因此,Fenton氧化能够促进后续的微生物修复。     

Effect of Sphingobium yanoikuyae B1 inoculation on bacterial community dynamics and polycyclic aromatic hydrocarbon degradation in aged and freshly PAH-contaminated soils

Sphingobium yanoikuyae B1 is able to degrade a range of polycyclic aromatic hydrocarbons (PAHs) and as a sphingomonad belongs to one of the dominant genera found in PAH-contaminated soils. We examined the ecological effect that soil inoculation with S. yanoikuyae B1 has on the native bacterial community in three different soils: aged PAH-contaminated soil from an industrial site, compost freshly contaminated with PAHs and un-contaminated compost. Survival of S. yanoikuyae B1 was dependent on the presence of PAHs, and the strain was unable to colonize un-contaminated compost. Inoculation with S. yanoikuyae B1 did not cause extensive changes in the native bacterial community of either soil, as assessed by denaturing gel electrophoresis, but its presence led to an increase in the population level of two other species in the aged contaminated soil community and appeared to have an antagonistic affect on several members of the contaminated compost community, indicating niche competition.     

Catalytic oxidation for air pollution control

Bench-scale experiments have been conducted to evaluate a series of titania-supported Pt-Pd (as oxides) catalysts in the presence and absence of MoO₃ and Fe₂O₃ additives for their effectiveness in the complete catalytic oxidation of volatile organic compounds (VOCs) in air likely to be found in waste gases. Under oxidizing conditions, all of the catalysts promoted the complete oxidation of VOCs to CO₂ and H₂O. 99 % Conversion was achieved with a C₂H₄-C₂H₆ gas mixture in air at temperatures between about 160–450 °C and at a space velocity of 20,000 h^?1. Oxidation activity for the titania supported catalysts were found to decrease in the order Pt-Pd-Mo-Fe > Pt-Pd-Mo > Pt-Pd-Fe > Pt-Pd. However, the addition of MoO₃ and Fe₂O₃ increase the catalyst activity and reduce the reaction temperature for the complete destruction. Ageing was also performed in order to study the stability of the most active catalyst. Pt-Pd-Mo-Fe (as oxides) on titania catalyst is effective in oxidizing a wide range of volatile organic compounds at relatively low temperatures (220–405 °C) and and at a space velocity of 40,000 h^?1 and is resistant to poisoning by halogenated and amine volatile organic compounds.     

Thermodynamics of interaction of lindane on silty loam and silty clay loam Indian soils

Abstract

Interaction of lindane with silty loam and silty clay loam soils was studied in batch tests at 23, 30 and 37° C. Sorption experiments were carried out at four concentrations and for varying time of contact upto 72 hours. This was followed by desorption studies. No desorption was observed. The sorption data was analysed using sorption equations and evaluating the thermodynamic parameters. The sorption was found to be predominantly entropic in nature and a combined effect of adsorption and chemisorption. The effect of organic matter and other chemical and mineralogical constituents of soils has also been discussed. The sorption with single application of lindane with the two soil types indicates that the insecticide is less likely to reach groundwater.     

粘土矿物材料吸附去除水中痕量邻苯二甲酸酯

研究了天然沸石、2种有机改性沸石及Mg/Al水滑石对水中痕量邻苯二甲酸二甲酯、邻苯二甲酸二(2-乙基己基)酯和邻苯二甲酸二辛酯的等温吸附情况和吸附机理,并与活性炭的吸附性能进行了比较。结果表明,Freundlich和Langmuir吸附等温方程均可以很好地描述天然沸石和Mg/Al水滑石对邻苯二甲酸酯的吸附,2种有机改性沸石对邻苯二甲酸酯的吸附更符合Linear吸附等温方程。与活性炭相比,天然沸石对邻苯二甲酸酯的吸附效果较差;2种有机改性沸石和Mg/Al水滑石对分子尺寸较小的邻苯二甲酸酯物质邻苯二甲酸二甲酯的去除率较低,分别低31.8%、31.4%和19.8%,但对分子较大的邻苯二甲酸酯物质邻苯二甲酸二(2-乙基己基)酯和邻苯二甲酸二辛酯的去除效果相差不大。     

Assessing strategies to mitigate phosphorus leaching from drained clay soils

Assessing mitigation of phosphorus (P) leaching from subsurface drainage systems is challenging due to high spatial and temporal variation in leaching. Mean measured total P leaching from a clayey soil in an eight-year study period (four replicates per treatment) was (kg ha^?1 year^?1): 1.21 from shallow autumn tillage (ShT), 0.84 from unfertilised fallow (UF), 0.81 from conventional autumn ploughing (CT) and 0.57 from structure liming (SL–CT). Treatment was not significant using Richards–Baker flow index or a distance factor as covariate (p = 0.084 and 0.057). A tendency for lower leaching was obtained comparing SL-CT with ShT (p _adjusted = 0.060 and 0.009 respectively). A combination of measures adapted to drainage conditions and clay content in different parts of the field is proposed since P leaching was approximately halved from an adjacent field (4.3 ha) in a three-year post-period compared with a three-year pre-period for structure liming the entire field and drainage system renovation plus structure lime drain backfilling.     

乳化液废水的均相催化湿式氧化

在2L的高温高压反应釜中,以非贵的过渡金属盐作均相催化剂,研究了高浓度难降解的乳化液废水的催化湿式氧化.试验发现,单一金属盐催化活性为Cu2 ＞Mn2 ＞Co2 ,其中Cu2 在200℃时催化效果良好,可使TOC去除率提高13.3%;Cu2 受投量影响较明显,以200mg/L为宜;混合盐催化活性为Cu2 Mn2 ≈Mn2 Co2 (＞Cu2 )＞Cu2 Co2 .     

Desorption kinetics studies on PAH-contaminated soil under varying temperatures

The purpose of this study was to investigate the effect of temperature on the release of polycyclic aromatic hydrocarbons (PAHs) from aged contaminated soil. The release of fluorene, phenanthrene, anthracene, fluoranthene and pyrene at 7, 15, 18 and 23 degrees C was studied using a column leaching method with a hydraulic retention time of 0.5 h. As the temperature declined from 23 to 7 degrees C the concentrations decreased by a factor of 11-12 for all the studied compounds except for anthracene, which only decreased by a factor 7. Rate constants at maximum release rate at the four studied temperatures were assessed. From temperature dependence studies, apparent activation energies of desorption, E*(des), were calculated. E*(des)-values appeared to be in the range of 105-137 kJ mol(-1) for the studied PAHs and increased with the LeBas molar volume of the compounds. The increase of E*(des) with increased molecular size indicates stronger sorption with increased hydrophobicity of the compounds.     

催化湿式氧化处理机械加工工业废水的研究

利用担载的双金属活性组分催化剂，考察了反应温度、压力、进料空速和污水pH等条件对催化湿式氧化处理某厂机械加工废水效果的影响。对于该厂的混合废水，在反应温度260℃，反应压力6．6MPa，空速为2．0h^-1，pH为3条件下处理后的废水CODCr去除率为90．2％。考察了助剂H2O2、絮凝剂对处理废水效果的影响和各种联用技术对废水的处理效果。     

Enrichment of trace elements in the clay size fraction of mining soils

Reactive waste dumps with sulfide minerals promote acid mine drainage (AMD), which results in water and soil contamination by metals and metalloids. In these systems, contamination is regulated by many factors, such as mineralogical composition of soil and the presence of sorption sites on specific mineral phases. So, the present study dedicates itself to understanding the distribution of trace elements in different size fractions (<2-mm and <2-μm fractions) of mining soils and to evaluate the relationship between chemical and mineralogical composition. Cerdeirinha and Penedono, located in Portugal, were the waste dumps under study. The results revealed that the two waste dumps have high degree of contamination by metals and arsenic and that these elements are concentrated in the clay size fraction. Hence, the higher degree of contamination by toxic elements, especially arsenic in Penedono as well as the role of clay minerals, jarosite, and goethite in retaining trace elements has management implications. Such information must be carefully thought in the rehabilitation projects to be planned for both waste dumps.