Axi-symmetric simulation of soil vapor extraction influenced by soil fracturing

Fracturing, either pneumatic or hydraulic, is a method to improve the performance of soil vapor extraction (SVE) in relatively low permeability soils (< 10(-5) cm/s). A two-dimensional model is presented to simulate trichloroethylene (TCE) soil vapor extraction modified by fracturing. Flow and transport is modeled using mobile macropore and micropore networks, which also have been identified in the literature as dual porosity, dual permeability, or heterogeneous flow models. In this model, fluids can flow in both the macropore and micropore networks. This represents a more general model compared to immobile micropore, mobile macropore models presented thus far in the literature for vapor flow and transport in two dimensions. The model considers pressure- and concentration-driven exchange between the macropore and micropore networks, concentration-driven exchange between the gas and sorbed phases within each network, and equilibrium exchange between the gas and water and a sorbed phase within each network. The parameters employed in an example simulation are based on field measurements made at a fractured site. Considered in the simulations were the influence of the volume percentage of fractures, the length of fractures, the relative location of the water table, and the influence of pulsed pumping. For these simulations, internetwork concentration-driven exchange most significantly affected mass removal. The volume percentage of fractures more significantly influence flow and mass removal than the length of fractures. The depth of the water table below the contamination plume only significantly influenced flow and mass removal when the water table was within 60 cm of the bottom of the contaminated soil in the vadose zone for the parameters considered in this study. Pulsed pumping was not found to increase the amount of mass removed in this study.     

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.     

Experimental determination of the kinetic rate law for the oxidation of perchloroethylene by potassium permanganate

Flushing soils contaminated with trichloroethylene (TCE) and perchloroethylene (PCE) with a permanganate (MnO₄⁻) solution has been shown to reduce the solvent content of the soil. Experiments were performed to quantify the rate at which KMnO₄ oxidizes aqueous solutions of PCE over a range of concentrations. In a series of homogeneous reactors, aqueous phase PCE concentrations were monitored over time in nine experimental trials with excess oxidant concentrations ranging from 5 to 30 g/l. Analysis of the data was performed to quantify the oxidation reaction order with respect to PCE and KMnO₄ and the reaction rate constant. The reaction between PCE and KMnO₄ was determined to be first-order with respect to both PCE and KMnO₄ with an overall specific reaction rate coefficient of 2.45±0.65 M⁻¹ min⁻¹.     

Humic acid enhanced remediation of an emplaced diesel source in groundwater. 1. Laboratory-based pilot scale test

The enhanced solubility of petroleum-derived compounds in humic acid solutions is the basis for a new groundwater remediation technology. In this unique pilot-scale test, a stationary contaminant source consisting of diesel fuel was placed below the water table in a model sand aquifer (1.2 x 5.5 x 1.8-m deep) and flushed with water at a flow rate of 2 cm/h over 5 years. At 51 days, laboratory grade humic acid was added to the water and maintained at a level of approximately 0.8 g/l. The addition of humic acid had only a small impact on the aqueous transport of the BTEX components, which were rapidly dissolved from the diesel, but had a large effect on the flushing of PAHs, including methylated naphthalenes (MNs). Binding to aqueous humic acid enhanced the solubilization of MNs two- to tenfold. During aqueous transport, biodegradation of the BTEX and PAHs occurred, limiting the lateral and longitudinal extent of the diesel contaminant plume in the model aquifer. It appears that through enhanced solubilization, the overall biodegradation rate of the MNs was increased. As the various MNs were depleted from the diesel source, the MN plume shrank and then disappeared.     

应用淡水发光菌研究二元重金属混合物的联合毒性

应用新型淡水发光菌一青海弧菌Q67(Vibrio qinghaiensis sp.nov-Q67)发光值的测定。对铜锌、铜汞、铜镉、铜镍等4种重金属混合物的联合毒性进行了评价。结果表明。铜锌混合物对Q67的联合毒性等于两者的毒性之和。作用方式表现为加和作用：铜汞、铜镉、铜镍3种混合物对Q67的联合毒性则表现为拮抗作用。     

Soil heavy metal pollution from Pb/Zn smelting regions in China and the remediation potential of biomineralization

Smelting activities pose serious environmental problems due to the local and regional heavy metal pollution in soils they cause. It is therefore important to understand the pollution situation and its source in the contaminated soils. In this paper, data on heavy metal pollution in soils resulting from Pb/Zn smelting (published in the last 10 years) in China was summarized. The heavy metal pollution was analyzed from a macroscopic point of view. The results indicated that Pb, Zn, As and Cd were common contaminants that were present in soils with extremely high concentrations. Because of the extreme carcinogenicity, genotoxicity and neurotoxicity that heavy metals pose, remediation of the soils contaminated by smelting is urgently required. The primary anthropogenic activities contributing to soil pollution in smelting areas and the progressive development of accurate source identification were performed. Due to the advantages of biominerals, the potential of biomineralization for heavy metal contaminated soils was introduced. Furthermore, the prospects of geochemical fraction analysis, combined source identification methods as well as several optimization methods for biomineralization are presented, to provide a reference for pollution investigation and remediation in smelting contaminated soils in the future.     

Estimating the combined toxicity of flufenacet and imazaquin to sorghum with pore water herbicide concentration

Combined toxicity of herbicides to non-target crops is usually resulted from their successive application. The present study was conducted to assess the combined toxicity of flufenacet (FLU) and imazaquin (IMA) to sorghum with their concentration in soil pore water. The concentrations that inhibited growth by 50% (IC50) of FLU and IMA individually and their combination estimated from the herbicide concentrations in soil pore water notably differed from those based on the amended concentrations, due to the decline in bioavailability resulting from adsorption of the herbicides onto soil. According to the amended concentrations, the combined effect of FLU and IMA in soil on sorghum growth was identified as additive action. Based on the concentration in soil pore water, however, it was determined to be antagonism, which was identical to that observed in a test using culture solution. The results revealed that pore water herbicide concentration might be an effective tool to assess the combined toxicity of herbicides in soil to rotational crops.     

湖北某重金属污染土壤稳定化/固化治理工程实例

为保证南水北调水源地水质安全,该项工程对湖北省郧县境内4个关停搬迁企业原址约16万m3重金属污染土壤进行了修复治理。污染土壤清挖标准为《展览会用地土壤环境质量标准》(HJ350—2007)A级标准,污染土壤无害化处理验收标准为浸出液浓度低于《地表水环境质量标准》(GB3838—2002)中IV类水体标准值。工程采用异位稳定化/固化技术对重金属污染土壤进行了无害化处理,所用稳定化/固化药剂为施工单位自主研发的硫系和铁系稳定化药剂;无害化处理后的近20万m3土壤采用安全填埋进行处置。工程的成功实施为南水北调库区水质安全提供了有力保障。     

环境损害评估中修复方案的费用效益分析

土壤、地下水和地表水等污染治理成本通常较高,但修复后会带来众多直接和间接效益,因此,在进行修复决策和环境损害评估时应当予以综合考虑。文章对环境修复成本效益分析的定义、目的和方法进行了阐述,并结合具体案例解释了环境修复成本效益分析的具体过程。修复成本通常依据价格指南、费用估算模型/软件、类似工程经验、承包商报价等进行估算,修复效益可采用享乐价格法,根据个人意愿为环境支付的费用,进行计算。案例研究结果表明,环境修复效益及其受益方并不是单一的,在进行较大规模的环境修复决策时,应由政府进行干预,并积极寻求各利益相关方的配合,综合评估其经济可行性。在环境损害评估中,也应形成多方协调机制,科学合理地评价修复方案的费用和效益,合理确定赔偿数额。     

The legacy of surface mining: Remediation,restoration, reclamation and rehabilitation

Surface mining is a global phenomenon. When dealing with the land disturbances caused by surface mining operations, the terms remediation, reclamation, restoration and rehabilitation (R4) are commonly used interchangeably or otherwise vaguely defined. Expectations associated with these terms may differ significantly from one stakeholder to another, however. Regulators, industry, environmental practitioners, local communities and the general public therefore stand to benefit from a precise terminology based on agreed-upon end-goals. The latter range from the avoidance of exposure to pollutants (remediation) to the full recovery of the original ecosystem (restoration). Although frequently claimed as the end-goal, restoration may often not be unachievable, because of altered hydrology, habitat fragmentation, contamination, climate change, prohibitive costs and other environmental and socio-economic boundary conditions. Mostly, the definitions of reclamation and rehabilitation may overlap in their definitions and approaches. Here we attempt the creation of a road-map that can clearly translate end-goals for each of the R4 terms. According to the definitions encountered and exposed here, reclamation, which aims to recover key ecosystem services and biogeochemical functions within a replacement ecosystem or rehabilitation, which implies a repurposing of the landscape, may be the best approaches to deal with surface mining legacies.