Investigation of polychlorinated biphenyl removal from contaminated soil using microwave-generated steam

A feasibility study of polychlorinated biphenyl (PCB) removal from contaminated soils using microwave-generated steam (MGS) was performed. Initial experimental results show that MGS effectively removed PCBs from contaminated soil with an overall removal efficiency of greater than 98% at a steam-to-soil mass ratio of 3:1. Removal efficiency was found to be dependent upon the amount of steam employed, expressed as a mass ratio of steam applied to soil mass. Evaporation was identified as a major mechanism in removing PCBs from the soil. Rapid expansion and evaporation of pore water by microwave dielectric heating accelerated evaporation rates of PCB molecules. Increased solubility of PCBs into the heated aqueous phase is also hypothesized. Together these effects increase mass-transfer rates, thus enhancing removal of PCBs from the soil.     

Application of microwave irradiation in the removal of polychlorinated biphenyls from soil contaminated by capacitor oil

The applicability of microwave irradiation in the removal of polychlorinated biphenyls (PCBs) from the soil heavily contaminated by capacitor oil was studied. Granular activated carbon (GAC) was added into the soil as a microwave-absorbing material to rapidly increase the temperature of the reaction system. Effects of sodium hypophosphite (SHP) and iron powder (IP) as reductants on PCB removal, as well as the effects of water content in soil, microwave power and the amount of GAC added were investigated. The results indicated that in the presence of SHP and GAC, about 80% of PCBs in soil were effectively removed by 10 min microwave irradiation, and the further addition of IP could raise the average removal efficiency to a higher level, more than 95%. In the removal of PCBs with the microwave/GAC/IP/SHP system, an appropriate amount of water proved to be helpful in promoting the removal of PCBs from soil by steam distillation and in acting as a co-solvent of SHP and H-donor of IP.     

Chromium and nickel mobilization from a contaminated soil using chelants

The mobilization of chromium and nickel from an industrial soil was investigated using two biodegradable chelants (citric acid and histidine), compared with a persistent one (ethylenediaminetetraacetic acid). Successive metal mobilizations were carried out in batch experiments. The main reactions involved were estimated by modeling the system with MINEQL+. For a single mobilization, citric acid was the most effective for Cr mobilization and EDTA for Ni. Their effectiveness could be explained by their ability to solubilize the mineral matrix and by the competition for the surfaces sites to desorb Cr(VI). Before and after the mobilizations, the distribution of metals was determined by a sequential extraction procedure. Only slight modifications were observed due to the low percentage of solubilized metal. A concentration of 0.05 mol L(-1) (citric acid and EDTA) allows a good compromise between metal mobilization and preservation of the soil mineral integrity.     

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。     

Solvent extraction for heavy crude oil removal from contaminated soils

A new strategy of heavy crude oil removal from contaminated soils was studied. The hexane-acetone solvent mixture was used to investigate the ability of solvent extraction technique for cleaning up soils under various extraction conditions. The mixtures of hexane and acetone (25 vol%) were demonstrated to be the most effective in removing petroleum hydrocarbons from contaminated soils and approx 90% of saturates, naphthene aromatics, polar aromatics, and 60% of nC₇-asphaltenes were removed. Kinetic experiments demonstrated that the equilibrium was reached in 5 min and the majority of the oil pollutants were removed within 0.5 min. The effect of the ratio between solvent and soil on the extraction efficiency was also studied and results showed that the efficiency would increase following the higher solvent soil ratio. Then the multistage continuous extraction was considered to enhance the removal efficiency of oil pollutants. Three stages crosscurrent and countercurrent solvent extraction with the solvent soil ratio 6:1 removed 97% oil contaminants from soil. Clearly the results showed that the mixed-solvent of hexane and acetone (25 vol%) with character of low-toxic, acceptable cost and high efficiency was promising in solvent extraction to remove heavy oil fractions as well as petroleum hydrocarbons from contaminated soils.     

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。     

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     

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。     

Activated soil filters for removal of biocides from contaminated run-off and waste-waters

Building facades can be equipped with biocides to prevent formation of algal, fungal and bacterial films. Thus run-off waters may contain these highly active compounds. In this study, the removal of several groups of biocides from contaminated waters by means of an activated soil filter was studied.A technical scale activated vertical soil filter (biofilter) with different layers (peat, sand and gravel), was planted with reed (Phragmites australis) and used to study the removal rates and fate of hydrophilic to moderate hydrophobic (log K_ow 1.8-4.4) biocides and biocide metabolites such as: Terbutryn, Cybutryn (Irgarol® 1051), Descyclopropyl-Cybutryn (Cybutryn and Terbutryn metabolite), Isoproturon, Diuron, and its metabolite Diuron-desmonomethyl, Benzo-isothiazolinone, n-Octyl-isothiazolinone, Dichloro-n-octylisothiazolinone and Iodocarbamate (Iodocarb). Three experiments were performed: the first one (36 d) under low flow conditions (61 L m⁻² d⁻¹) reached removal rates between 82% and 100%. The second one was performed to study high flow conditions: During this experiment, water was added as a pulse to the filter system with a hydraulic load of 255 L m⁻² within 5 min (retention time <1 h). During this experiment the removal rates of the compounds decreased drastically. For five compounds (Cybutryn, Descyclopropyl-Cybutryn, Diuron, Isoproturon, and Iodocarb) the removal dropped temporarily below 60%, while it was always above 70% for the others (Terbutryn, Benzo-isothiazolinone, n-Octyl-isothiazolinone, Dichloro-n-octylisothiazolinone). However, this removal is a considerable improvement compared to direct discharge into surface waters or infiltration into soil without appropriate removal. In the last experiment the removal efficiencies of the different layers were studied. Though the peat layer was responsible for most of the removal, the sand and gravel layers also contributed significantly for some compounds. All compounds are rather removed by degradation than by sorption.     

油污土壤中柴油去除的影响因素

以柴油为污染物,通过一维砂柱实验模拟油污土壤中柴油去除过程,从油水界面张力(IFT)角度分析溶液pH、淋滤速度和表面活性物质对除油效果的影响。结果表明,延长油水接触时间、升高或降低蒸馏水pH值均使油水界面张力下降,低淋滤速度下单位孔隙体积水中石油浓度较大,而水溶液pH的变化对除油效果影响不明显。十二烷基硫酸钠(SDS)和乙醇使油水界面张力显著下降,因此表面活性物质的除油效率明显高于蒸馏水,乙醇溶液的除油效率随着体积浓度的增加而升高。从石油释放动力学方程计算的柴油累积释放量看,50%乙醇除油效率最高,8 mmol/L SDS溶液次之,在淋洗初期柴油去除效果最为明显,而在中期和后期除油率增加幅度逐渐减小。     

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%。     

有色金属冶炼厂镉污染土壤淋洗除镉

以云南省某废弃有色金属冶炼厂镉污染土壤为研究对象,分别采用单一淋洗和复合淋洗方法探究盐酸、FeCl3、鼠李糖脂淋洗剂及淋洗条件对土壤中镉去除效果的影响。结果表明,在盐酸(1 mol·L-1)+鼠李糖脂(2%)配比为2∶1,液固比为8∶1,淋洗时间为24 h的条件下,土壤中镉的去除率可达86.78%,可将镉污染强度为1 180 mg·kg-1的土壤修复至满足《土壤环境质量建设用地土壤污染风险管控标准》(GB 36600-2018)第二类用地管制值(Cd-1)的要求。该方法可有效去除土壤中活性态镉,使土壤生物毒性明显降低。     

可渗透反应复合电极法对土壤重金属的电动去除

将零价铁(Fe0)、沸石等活性材料附着在电极上形成可渗透反应层并构成可渗透反应复合电极,采用不同的复合电极对Cd2+、Ni 2+、Pb2+和Cu2+等4种阳离子型重金属污染土壤进行了电动力学修复。研究了不同可渗透反应复合电极对土壤pH的控制效果以及对重金属的去除作用,分析了迁移到复合电极中的重金属形态变化。结果表明,复合电极中添加酸、碱性沸石并适时更换,可有效中和、截留阴阳极电解产生的OH-和H+,避免或减缓土壤酸碱迁移带的形成,防止重金属离子的过早沉淀及土壤过度酸化,极大提高了重金属的去除率。复合电极中Fe0可将迁移进来的重金属离子进行还原稳定,实现重金属污染物的捕获与固定,与迁移到沸石复合电极中的4种重金属不稳定态相比,"Fe0+沸石"复合电极中重金属不稳定态分别下降了61.4、60.5、61.4、57.1百分点。结果还显示,阴极采用"Fe0+沸石"复合电极并适时进行更换,施加1.5V/cm的直流电压修复10d后,土壤中Cd、Ni、Pb、Cu的总去除率分别为44.5%、41.5%、33.5%和36.7%,且进一步延长修复时间和持续更换电极可获得更为理想的修复效果。     

Conditions for effective removal of pyrene from an artificially contaminated soil using Pseudomonas aeruginosa 57SJ rhamnolipids

The efficacy of a new rhamnolipid biosurfactants mixture to enhance the removal of pyrene from a soil artificially contaminated was investigated. The molar solubilization ratio (MSR) and the partition coefficient between the micelles and water (log K(m)) were found to be 7.5 x 10(-3) and 5.7, respectively. From soil column studies, the pyrene removal increased linearly with the concentration of the injected biosurfactants solution above the effective critical micellar concentration (0.4 g L(-1)). Flushing with a 5.0 g L(-1) biosurfactants solution increased the pyrene concentration in the effluent by 178 times. At high biosurfactants' concentrations (2.5 and 5.0 g L(-1)), the cumulative pyrene recovery reached 70%. This pyrene remobilization takes place independently of the soil organic carbon solubilization. This study provides a combination of batch and column experiments in order to find the conditions for effective soil remediation using a new rhamnolipids mixture.     

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.     

Bioremediation of soil contaminated with polynuclear aromatic hydrocarbons (PAHs): a review

Polynuclear aromatic hydrocarbons (PAHs) constitute a group of priority pollutants which are present at high concentrations in the soils of many industrially contaminated sites. Criteria established for the removal or treatment or both of soils contaminated with PAHs vary widely within and between nations. The bioremediation of contaminated soils with in-situ, on-site, and bioreactor techniques is reviewed, together with the factors affecting PAH degradation. Current in-situ remediation techniques are considered ineffective for the removal of most PAHs from contaminated soil. On-site 'landforming' methods have been used successfully (and within a reasonable period of time) to degrade only those PAHs with three or fewer aromatic rings. Bioreactors have proved most effective for soil remediation, since conditions for enhanced degradation can be achieved most readily. However, bioreactors are still at the development stage, and further research is required to optimise their efficiency and economy for routine use. Degradation of the more recalcitrant high-molecular-weight PAHs is contaminated soil has not been particularly successful to date. Further research needs are identified to help develop bioremediation into a most cost-effective technology. The importance of full site assessments and treatability studies for successful application in the field is emphasised.     

应用活性炭再生含多环芳烃植物油的可行性及性能评价

为利用植物油去除污染土壤中的多环芳烃,研究了应用活性炭F400吸附柱再生含多环芳烃植物油的可行性,对含高浓度多环芳烃的植物油进行二级再生处理,优化了过程参数,比较了原植物油和经活性炭再生的植物油去除土壤中多环芳烃能力的差别.结果表明,活性炭吸附法可以实现含多环芳烃植物油的再生,证明了修复策略的可行性.二级处理可以进一步吸附植物油中的多环芳烃,且高分子量多环芳烃几乎完全被去除.再生植物油和原植物油去除土壤中多环芳烃的能力没有明显差别.     

Combined chemical and biological treatment of oil contaminated soil

Combined chemical (Fenton-like and ozonation) and biological treatment for the remediation of shale oil and transformer oil contaminated soil has been under study. Chemical treatment of shale oil and transformer oil adsorbed in peat resulted in lower contaminants' removal and required higher addition of chemicals than chemical treatment of contaminants in sand matrix. The acidic pH (3.0) conditions favoured Fenton-like oxidation of oil in soil. Nevertheless, it was concluded that remediation of contaminated soil using in situ Fenton-like treatment will be more feasible at natural soil pH. Both investigated chemical processes (Fenton-like and ozonation) allowed improving the subsequent biodegradability of oil. Moderate doses of chemical oxidants (hydrogen peroxide, ozone) should be applied in combination of chemical treatment (both, Fenton-like or ozonation) and biotreatment. For remediation of transformer oil and shale oil contaminated soil Fenton-like pre-treatment followed by biodegradation was found to be the most efficient.     

Process evaluation for optimization of EDTA use and recovery for heavy metal removal from a contaminated soil

This study aimed to establish an optimized, closed loop application of ethylenediaminetetraacetic acid (EDTA) in heavy metal removals from a contaminated soil through integrating EDTA recovery/regeneration and metal precipitation processes in the treatment train. Three divalent heavy metals were investigated, namely, Pb, Cd, and Ni. The extractability of the metals by EDTA followed the decreasing order of CdPb>Ni. The first part of this study was to search for the optimal use of the fresh EDTA in removing these heavy metals from the contaminated soil. The second part of this study was devoted to the recovery/regeneration of the spent EDTA which followed the sequential processes involving (1) complex destabilization by adding ferric ion (Fe(III)) to liberate Pb, Cd, and Ni, (2) precipitation of the liberated Pb, Cd, and Ni in phosphate (PO4(3-)) forms, and (3) precipitation of the excess Fe(III) which eventually produced free EDTA for reuse. The process variables were dosages of Fe(III) and PO4(3-), pH and reaction times. Laborious trial experiments would be needed in searching for the optimum conditions for the above processes. To expedite this exercise, a geochemical equilibrium model, MINTEQA2, was used to find the thermodynamically favorable conditions for recoveries of both EDTA and heavy metals. This was then followed by experimental examination of the process kinetics to observe for the optimal reaction time for each thermodynamically favorable process. This study revealed that 2 h of reaction time each for the complex destabilization reaction and the metal phosphate precipitation reaction was sufficient to achieve equilibrium. With the optimized process condition identified in this study, a total of 95%, 89% and 90% of the extracted Pb, Cd and Ni, respectively, could be precipitated from the spent EDTA solution, with 84% EDTA recovery. The reused EDTA maintained more than 90% of its preceding extraction power in each cycle of reuse.