Degradation of polycyclic aromatic hydrocarbons (PAHs) in an aged coal tar contaminated soil under in-vessel composting conditions

In-vessel composting of polycyclic aromatic hydrocarbons (PAHs) present in contaminated soil from a manufactured gas plant site was investigated over 98 days using laboratory-scale in-vessel composting reactors. The composting reactors were operated at 18 different operational conditions using a 3-factor factorial design with three temperatures (T, 38 degrees C, 55 degrees C and 70 degrees C), four soil to green waste ratios (S:GW, 0.6:1, 0.7:1, 0.8:1 and 0.9:1 on a dry weight basis) and three moisture contents (MC, 40%, 60% and 80%). PAH losses followed first order kinetics reaching 0.015 day(-1) at optimal operational conditions. A factor analysis of the 18 different operational conditions under investigation indicated that the optimal operational conditions for degradation of PAHs occurred at MC 60%, S:GW 0.8:1 and T 38 degrees C. Thus, it is recommended to maintain operational conditions during in-vessel composting of PAH-solid waste close to these values.     

Behavior of PAHs during cold storage of historically contaminated soil samples

The stability of historically polycyclic aromatic hydrocarbon (PAH)-contaminated soils during cold storage was investigated. Samples from two former manufactured gas plants exhibited quantitative recoveries of PAHs over the whole period of sample holding at 4 °C in the dark (8–10 months), whereas significant losses of PAHs were observed for soils received from a former railroad sleeper preservation plant with low molecular weight compounds being notably more affected compared to heavier PAHs. Already after 2 weeks of holding time, 3-ring PAHs in one of theses samples were down to 29–73% of the initial concentration and significant losses were observed for up to 5-ring compounds. Dissipation of PAHs was found to be predominantly due to aerobic microbial metabolism since sodium azide poisoned samples showed quantitative recoveries for all PAHs over the entire storage time of 3 months. A similar stabilizing effect was observed for freezing at −20 °C as means of preservation. Except for acenaphthene, no significant loss for any of the PAHs was observed over 6 weeks of holding time. Eventually, selected chemical, physical, and biological parameters of two soils were investigated and identified as potential indicators for the stability of PAH-contaminated soil samples.     

Evolution of bacterial community during bioremediation of PAHs in a coal tar contaminated soil

The monitoring of a windrow treatment applied to soil contaminated by mostly 2-, 3- and 4-ring PAHs produced by coal tar distillation was performed by following the evolution of both PAH concentration and the bacterial community. Total and PAH-degrading bacterial community structures were followed by 16S rRNA PCR-DGGE in parallel with quantification by bacterial counts and 16 PAH measurements. Six months of biological treatment led to a strong decrease in 2-, 3- and 4-ring PAH concentrations (98, 97 and 82% respectively). This result was associated with the activity of bacterial PAH-degraders belonging mainly to the Gamma-proteobacteria, in particular, the Enterobacteria and Pseudomonas genera, which were detected over the course of the treatment. This group was considered to be a good bioindicator to determine the potential PAH biodegradation of contaminated soil. Conversely, other species, like the Beta-proteobacteria, were detected after 3months, when 2-, 3- and 4-ring PAHs were almost completely degraded. Thus, presence of the Beta-proteobacteria group could be considered a good candidate indicator to estimate the endpoint of biotreatment of this type of PAH-contaminated soil.     

Effects of polycyclic aromatic hydrocarbons on germination and subsequent growth of grasses and legumes in freshly contaminated soil and soil with aged PAHs residues

The relevance of germination trials for screening plants that may have potential for use in the phytoremediation of PAH contaminated land was evaluated. The germination and subsequent growth of 7 grass and legume species were evaluated in soil spiked with a pure PAH mixture or coal tar and soil from a former coking plant heavily contaminated with aged PAHs. None of these treatments adversely affected germination of the plants. However, apart from Lolium perenne all species exhibited reduced growth in the coking plant soil after 12 weeks growth when compared to the untreated soil. In the coal tar spiked soil 4 out of the 7 species showed reduced growth, as did 3 out of the 7 in the soil spiked with a mixture of 7 PAHs. Therefore, germination studies alone would not predict the success of subsequent growth of the species tested in the ranges of soil PAH levels studied.     

Investigation of organic matter dynamics during in-vessel composting of an aged coal-tar contaminated soil using fluorescence excitation-emission spectroscopy

In-vessel composting of an aged coal-tar contaminated soil from a manufactured gas plant site was investigated over 98days using laboratory-scale in-vessel composting reactors. The composting reactors were operated at 18 different operational conditions using a logistic three-factor factorial design with three temperatures (T=38, 55 and 70 degrees C), four soil to green waste ratios (S:GW; 0.6:1, 0.7:1, 0.8:1 and 0.9:1 on a dry weight basis) and three moisture contents (MC; 40%, 60% and 80%). Excitation-emission matrix (EEM) fluorescence spectroscopy was used to investigate organic matter dynamics in the composting mixture. The results of this investigation indicated that formation of humic substances can be monitored by fluorescence excitation-emission matrix, and provided evidence of progressive mineralization or humification of the composting mixture. Peak excitation wavelength shifts and peak fluorescence intensity can both be used as indicators to monitor the humification or maturation of compost. Finally, the fluorescence index can be applied to investigate the origin of humic substances and fulvic acids, and the humification or maturation of compost.     

The differential removal of aged polycyclic aromatic hydrocarbons from soil during bioremediation

Composting for the removal of polycyclic aromatic hydrocarbons (PAH) from soil was assessed as a treatment option at a former tar contaminated site, alongside conventional land treatment. The key objective of the study was to illustrate differences in the extent of removal of the different PAH compounds undergoing biological treatment. Soil composting led to more extensive PAH removal than did 2 variations on the land treatment process. Soil composting was substantially more effective in removing benzo(a)anthracene, chrysene, benzo(b+k)fluoranthene, benzo(a)pyrene, dibenz(ah)anthracene, indenopyrene and benz (gih)perylene, than the land treatment processes. The extents of removal of these higher molecular weight PAH were at least 50% over the 7 month treatment period where composting was used, whereas degradation did not exceed 5% for each of these PAH compounds in the land treatments over the same period. Implications from the study for the practical and effective composting of PAH compounds in soil, are (1) moisture in the soil-compost mix should be kept constant, (2) fresh organic matter should be used and (3) efforts need to be made to ensure soil is properly homogenized, both prior to and during soil mixing.     

环境胁迫因子对固定菌修复污染土壤效果的研究

通过对环境胁迫因子参数的不同设定,对固定菌修复污染土壤效果进行了研究.结果显示,当环境胁迫因子温度(高温40 ℃和低温15 ℃)、酸碱度(pH＝4和pH＝9)及重金属(Cd和Pb)存在时,对固定菌降解污染物的影响并不大,而游离菌降解率却有一定的下降趋势.进一步观察了固定化载体内部微观结构,为固定菌用于有机污染土壤的异位修复提供了一定的理论基础.     

Impact of microbial activity on copper, lead and nickel mobilization during the bioremediation of soil PAHs

A fungal bioremediation method using P. frequentans removed up to 75% of phenanthrene with the addition of water and nutrients over a period of 30 d. During the bioremediation process, changes in metal behavior were monitored by an in situ technique (diffusive gradients in thin-films, DGT) and by soil solution chemistry. DGT provided absolute data on fluxes from the solid phase to the DGT device and relative trends of concentrations of the most labile metal species. DGT response indicated that bioremediation increases metal mobilization from the solid phase. Filtration provided data on the concentrations of solution phase (<0.45 microm) metal. In all case, metal fluxes and concentrations significantly increased after the bioremediation process began. Fluxes increased from <0.1 pg cm(-2)s(-1) before bioremediation to between 0.2 and 0.5 pg cm(-2)s(-1) after bioremediation. Metal concentrations in the soils solution (filtration at 0.45 microm) increased from 2 to 10 microg l(-1) (Cu), 1-4 microgl(-1) (Pb) and from 40 to 140 microg l(-1) (Ni) after bioremediation. Although over a short time period, these data strongly indicated that there was remobilization of metal from solid to solution (and thus to the DGT device) directly due to the bioremediation process. Although the mechanism was not unambiguously identified, it was shown not to be related to small changes in bulk pH over time and was attributed to the microbial action on the surface of the soil solid phase, releasing metal into solution. Additionally, differences in metal concentration and flux were observed in sterilized and non-sterilized soils and in the absence or presence of phenanthrene. The results indicated that the bioremediation of soil by P. frequentans increased the flux, lability and mobility of trace metal species and therefore the likely metal bioavailability to plants.     

PAHs污染土壤的热修复可行性

以某煤制气厂污染场地中16种US EPA优先控制多环芳烃（Σ16 PAHs）为目标污染物进行了热修复批量实验和可行性实验。热修复批量实验结果表明,当热修复温度为400 ℃、加热时间为8 h时,土壤中的Σ16 PAHs去除率达99.9%。热修复可行性实验选择重污染、中污染和轻污染土壤以400 ℃作为目标温度,恒温72 h进行实验。热修复前后不同程度污染土壤的Σ16 PAHs的总去除率均可达到99.9%,但重污染土壤浓度非常高,部分苯并类物质未达到修复目标值,需进一步延长加热时间或提高加热温度保证达到修复目标值。土壤土工参数影响分析结果表明,热修复后土壤颗粒粒径呈增大趋势,土壤稳定性、抗压强度均增强。此外,土壤中可溶性盐含量增多,盐渍化程度增大。     

Butanol extraction to predict bioavailability of PAHs in soil

The feasibility of a mild-solvent extraction procedure to predict the bioavailability of individual polycyclic aromatic hydrocarbons (PAHs) in soil was assessed. The quantities that were degraded during the course of biodegradation of phenanthrene and pyrene in soil with or without plants correlated with the amounts extracted by n-butanol, with R2 values of 0.971 and 0.994, respectively. Six consecutive groups of earthworms removed ca. 70% of the pyrene remaining after extensive biodegradation, a value similar to the quantity extracted by n-butanol. The amount of chrysene aged in sterilized soil that was extracted by n-butanol was not statistically different from the quantities assimilated by earth-worms (Eisenia fetida) introduced into the soil. Such a mild extraction procedure may be useful as a means of predicting PAH bioavailability.     

高锰酸钾修复PAHs污染土壤过程中Mn迁移转化规律

为探究高锰酸钾氧化修复技术应用过程中Mn元素迁移转化规律及其潜在的环境风险,通过室内模拟实验,采用某焦化厂PAHs污染土壤作为研究材料,探究了高锰酸钾修复技术中不同药剂投加量对PAHs去除、高锰酸钾消耗量、土壤中Mn质量分数、Mn赋存形态分布及有效态Mn质量分数等的影响。结果表明,高锰酸钾氧化处理可有效去除土壤中PAHs;当高锰酸钾投加量为0.20 mmol·g⁻¹、反应时间为1 d时,PAHs去除率最高,可达89.61%。氧化处理过程中,高锰酸钾消耗量和土壤Mn质量分数均与高锰酸钾的投加量有关,随投加量增加而升高。其中,土壤Mn的质量分数与高锰酸钾消耗量呈显著正相关关系。高锰酸钾氧化处理后土壤中Mn主要以铁锰氧化物结合态存在,所占比例为77.04%~92.17%。土壤经0.05 mmol·g⁻¹高锰酸钾氧化处理后,土壤有效态Mn的质量分数比对照组增加了0.94倍;而在高锰酸钾投加量为0.10~0.40 mmol·g⁻¹的处理条件下,土壤有效态Mn的质量分数下降了77.65%~99.09%。药剂投加量是影响高锰酸钾氧化修复PAHs污染土壤过程中Mn环境行为的关键因子。本研究结果可为高锰酸钾氧化修复技术应用工艺优化提供参考。     

Phytoremediation of an aged petroleum contaminated soil using endophyte infected and non-infected grasses

Phytoremediation is a promising technique for cleaning petroleum contaminated soils. In this study, the effects of two grass species (Festuca arundinacea Schreb. and Festuca pratensis Huds.), infected (E(+)) and non-infected (E(-)) by endophytic fungi (Neotyphodium coenophialum and Neotyphodium uncinatum, respectively) on the degradation of petroleum hydrocarbons in an aged petroleum contaminated soil was investigated. Plants were grown in the soil for 7 months and unplanted soil considered as control. At the end of the experiment, total and oil-degrading bacteria, dehydrogenase activity, water-soluble phenols, total petroleum hydrocarbons (TPH) and polycyclic aromatic hydrocarbons (PAHs) contents were measured in the soil. The results demonstrated that E(+) plants contained more root and shoot biomass than E(-) plants and created higher levels of water-soluble phenols and dehydrogenase activity in the soil, while there was no significant difference in bacterial counts of planted soils. Planting stimulated total and oil-degrading bacterial numbers, dehydrogenase activity and the soil content of water-soluble phenols. Regardless of endophyte infection, PAH and TPH removal in the rhizosphere of plants were 80-84 and 64-72% respectively, whereas the removals in controls were 56 and 31%, respectively. It was revealed that TPHs in retention time range of n-alkanes with C(10)-C(25) chain lengths and TPH were more degraded in the rhizosphere of E(+) plants compared to E(-) ones. Thus, grasses infected with endophytic fungi could be more efficient for removal of TPH from oil-contaminated soils.     

工业化规模生物堆修复焦化类PAHs污染土壤的效果

现场建立处理能力为450 m3工业化规模的生物堆对焦化类PAHs污染土壤进行为期8个月的修复,运行过程中控制土壤C∶N∶P=100∶10∶1、水分10%～20%(质量百分比)、堆内氧气不低于7%(体积百分比)。结果表明:O2与CO2浓度呈负相关。系统连续运行时,微生物数量增加至107数量级,高出自然状态下土壤中微生物数量1～2个数量级。除NO3-在运行后期显著增加外,其余土壤因子均无明显变化。PAHs的降解主要出现在前6个月,之后进入"拖尾"阶段,土壤中各PAH浓度基本不再降低。运行结束后,堆体0.5 m处土壤中含2、3、4、5和6个苯环PAHs的降解率分别介于56.3%～99.5%、34.8%～71.6%、30.7%～40.6%、28.6%～39.2%和39.3%,16种PAHs的平均去除率为65.1%。1.5 m处土壤中含2、3、4、5和6个苯环PAHs的降解率分别介于50.9%～99.8%、57.7%～60.9%、55.9%～63.0%、27.3%～57.1%和52.2%,16种PAHs的平均去除率为71.4%。     

某电子垃圾拆解园周边农田土壤中多环芳烃的污染特征及风险评估

研究了某电子垃圾拆解园周边151个农田土壤样品中16种多环芳烃(PAHs)的污染特征和环境风险。结果表明,125个表层土壤样品中PAHs总质量浓度在149.0~2.0×104μg/kg,均值为1 805.5μg/kg,随着剖面土壤深度增加,PAHs含量总体呈递减趋势。通过来源解析,电子拆解园周围土壤中PAHs污染主要由废弃的电子电器元件的粗放燃烧和汽车尾气排放共同引起。土壤风险评估表明,7种类二噁英毒性PAHs的毒性当量(TEQPAH)在6.000×10-5~0.689pg TEQ/g,平均值为0.015pg TEQ/g;苯并(a)芘、二苯并(a,h)蒽、苯并(a)蒽、苯并(b)荧蒽、茚并(1,2,3-cd)芘致癌风险率超出百万分之一的样本比例分别为20.53%、6.62%、1.99%、2.65%、2.65%,其中采样点1、68两个点位表层土壤的苯并(b)荧蒽致癌风险率超过了万分之一。     

表面活性剂对焦化污染土壤中多环芳烃淋洗修复研究

异位土壤淋洗是一种高效修复污染土壤技术。以孝义市某焦化厂污染土壤为研究对象,采用批处理实验,探究表面活性剂曲拉通-100(TX-100)、吐温80(TW80)、烷基糖苷(APG)作为淋洗剂对土壤中16种多环芳烃(PAHs)的淋洗效果,并以TW80为代表,考察了淋洗剂浓度、淋洗时间、pH以及淋洗方式对污染土壤中PAHs的去除效果。结果表明,TW80、TX-100和APG对土壤中16种PAHs的总去除率分别为25.67%、18.89%和16.77%。TW80作为淋洗剂,3环PAHs的去除率低于高环(3环)PAHs,主要与焦化污染土壤中以3环PAHs为主有关;高环PAHs随着环数的增加,去除率降低。焦化污染土壤中PAHs的去除在240min达到平衡;大部分PAHs去除率随TW80浓度的增加而增大;pH可不作调整;在TW80用量相同情况下,建议采用单次淋洗。     

Reducing plant uptake of PAHs by cationic surfactant-enhanced soil retention

Reducing the transfer of contaminants from soils to plants is a promising approach to produce safe agricultural products grown on contaminated soils. In this study, 0-400 mg/kg cetyltrimethylammonium bromide (CTMAB) and dodecylpyridinium bromide (DDPB) were separately utilized to enhance the sorption of PAHs onto soils, thereby reducing the transfer of PAHs from soil to soil solution and subsequently to plants. Concentrations of phenanthrene and pyrene in vegetables grown in contaminated soils treated with the cationic surfactants were lower than those grown in the surfactant-free control. The maximum reductions of phenanthrene and pyrene were 66% and 51% for chrysanthemum (Chrysanthemum coronarium L.), 62% and 71% for cabbage (Brassica campestris L.), and 34% and 53% for lettuce (Lactuca sativa L.), respectively. Considering the impacts of cationic surfactants on plant growth and soil microbial activity, CTMAB was more appropriate to employ, and the most effective dose was 100-200 mg/kg.     

老化石油污染土壤的清洗处理

以华北油田老化长达1年以上的石油污染土壤为研究对象,采用自行选配的清洗剂对该污染土壤进行了一次清洗和二次清洗处理.实验结果表明,一次清洗后,污染土壤样品的含油率从26.34%～29.90%降到6.34%～7.84%,洗油率达80.06%～81.06%;经二次清洗处理后,污染土壤样品的含油率从26.34%～29.90%降到4.05%～4.85%,洗油率达88.06%～88.19%.在一次清洗和二次清洗的基础上,通过模拟实验确定了洗油污水回用的最佳回用率为80%,最佳加药质量浓度为0.4 g/L,该条件下污水的最终产生量也较少.按照该参数对华北油田的石油污染土壤进行了清洗实验,洗油率达79.20%～80.51%.     

多环芳烃污染土壤的植物与微生物修复研究进展

概括介绍了多环芳烃污染土壤的植物修复、微生物修复和植物 微生物联合修复的原理、优缺点、影响因素及国内外研究进展 ,并对生物修复的未来发展进行了展望     

The influence of defoamer on removal of PAHs in soil washing

The use of surfactants during soil washing process can create massive foam, which has a negative impact on the effective use of equipment. A series of tests was conducted to evaluate the defoaming performance of three defoamers and to investigate the influence on removal of polycyclic aromatic hydrocarbons (PAHs) during enhanced soil washing by the addition of the defoamer. Results showed that polydimethylsiloxane oil, which is the most common biomaterial used in commercial antifoaming and defoaming agents, has the best defoaming performance. With the addition of 0.1% polydimethylsiloxane oil, the removal ratios of total 16 PAHs (ΣPAHs) increased up to 53.48% and 75.92% when washing time was 5 min and 30 min, respectively, compared with the removal ratios of 44.12% and 67.28% with Triton X-100 solution only. This indicated that the proper selection of defoamer not only solves massive foaming problem but also brings out a positive influence on PAH removal during the soil washing process.

Implications: Three kinds of defoamers (kieselguhr, dodecanol, and polydimethylsiloxane oil) were collected to destroy the foam produced by Triton X-100. Among those defoamers, the polydimethylsiloxane (PDMS) oil has the best defoaming performances. The surface tension of the Triton X-100 solution with the addition of PDMS was lower. The addition of PDMS could improve the removal ratio of ΣPAHs during soil washing. That may be attributed to the addition of the nonionic surfactant Tergitol NP-10 as the emulsifier in the defoamer. After all, the results do not provide any indication of the influence on the solubilization micelles. It is thus questionable whether other components of PDMS oil could improve the PAH solubilization.     

Effect of soil aggregation on the biodegradation of phenanthrene aged in soil

A study was conducted to determine the possible role of soil aggregates in the sequestration of phenanthrene and thus in the declined biodegradation of the hydrocarbon. Phenanthrene aged in Lima loam (2-mm aggregates) showed declined biodegradation with time of aging to the test bacterium P5-2 capable of using sorbed phenanthrene. In contrast, the compound aged in a soil reconstructed with 68% clay-silt and 32% sand that had been separated from the Lima loam was readily mineralized. The percentages of each fraction used were the same as those of the original soil. Biodegradation of aged phenanthrene was not affected significantly by varying the ratios of each fraction in reconstructed mixtures. In experiments with Lima loam, its clay-silt fraction, and its sand fraction, mineralization extent was much lower in soil aggregates compared with the other samples while all had similar organic carbon content of ca. 1.51%. This suggests that aggregation may be another important determinant in the reduced biodegradation of aged phenanthrene.