Sinkholes and the engineering and environmental impacts of karst : proceedings of the ... Multidisciplinary Conference on Sinkholes and the Engineering and Environmental Impacts of Karst. Multidisciplinary Conference on Sinkholes and th...最新文献
Pub Date : 2018-04-01DOI: 10.5038/9780991000982.1043
Mohammad Shokri, D. Vesper, E. Herman, Ljiljana M. Rajić, Kimberly L Hetrick, I. Padilla, A. Alshawabkeh
Sediments are ubiquitous in karst systems and play a critical role in the fate and transport of contaminants. Sorbed contaminants may be stored on immobile sediments or rapidly dispersed on mobile sediments. Sediments may also influence remediation by either enhancing or interfering with the process. To better understand the potential effects of sediments on remediation, we conducted physical and chemical characterizations of 11 sediment samples from 7 cave and spring deposits from karst regions of Tennessee, Virginia, and West Virginia. The samples were analyzed for particle-size distribution using sieves and laser diffraction particle analysis. The sediment size fraction <2 mm (sand, silt, and clay) was analyzed for slurry pH and specific conductivity (SC) using electrodes and for bulk total carbon, organic carbon, nitrogen and sulfur on an ElementarTM Vario MAX Cube CNS. The same <2 mm fraction was subjected to a pseudo-total extraction using aqua regia with subsequent solution analysis by inductively coupled plasma-optical emission spectrometry (ICP-OES). Most of the samples were dominated by the <2 mm size fraction. Their slurry pHs ranged from 6.8 to 8.4 and their SCs ranged from 45 to 206 μS/cm with the exception of two high SC samples (726 and 8500 μS/cm). The fraction of organic carbon (Foc) in the sediments ranged from <0.1 to 2%. The sample from a saltpeter cave historically used for gunpowder production contained the highest concentrations of N and S (~3 g/kg) but lower total C than some of the spring samples. The pseudo-total extractions were analyzed for Al, Ca, Fe, Mg, and Mn. Of those elements, Mg was the most consistent across the locations (2.0-6.1 g/kg), and Ca was the most variable (1.4-52 g/kg). Given the importance of particle size and elemental concentrations in chemical reactions and remediation, more data of this type are needed to predict contaminant fate and transport and to plan successful remediation projects.
沉积物在喀斯特系统中无处不在，对污染物的命运和运移起着至关重要的作用。被吸附的污染物可以储存在固定的沉积物上，也可以迅速分散在流动的沉积物上。沉积物也可能通过加强或干扰修复过程来影响修复。为了更好地了解沉积物对修复的潜在影响，我们对来自田纳西州、弗吉尼亚州和西弗吉尼亚州喀斯特地区7个洞穴和泉水沉积物的11个沉积物样品进行了物理和化学表征。采用筛分法和激光衍射粒度分析法分析样品的粒度分布。沉积物粒径< 2mm(砂、淤泥和粘土)使用电极分析了浆液pH值和比电导率(SC)，并在ElementarTM Vario MAX Cube CNS上分析了总体总碳、有机碳、氮和硫。同样的< 2mm的部分用王水进行伪全萃取，随后用电感耦合等离子体光学发射光谱(ICP-OES)进行溶液分析。大多数样品以< 2mm粒度的组分为主。矿浆ph值为6.8 ~ 8.4,SC值为45 ~ 206 μS/cm，高SC值为726和8500 μS/cm。沉积物中有机碳(Foc)含量在<0.1 ~ 2%之间。来自历史上用于火药生产的硝石洞穴的样品含有最高浓度的N和S (~3 g/kg)，但总C低于一些春季样品。伪总萃取分析了Al, Ca, Fe, Mg和Mn。其中，Mg在不同地点的含量最一致(2.0 ~ 6.1 g/kg)， Ca变化最大(1.4 ~ 52 g/kg)。考虑到颗粒大小和元素浓度在化学反应和修复中的重要性，需要更多这类数据来预测污染物的命运和运输，并规划成功的修复项目。
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Pub Date : 2018-04-01DOI: 10.5038/9780991000982.1017
Kimberly L Hetrick, Ljiljana M. Rajić, A. Alshawabkeh, Mohammad Shokri, D. Vesper
Due to the complicated nature of karst aquifers, many groundwater treatment technologies are difficult to implement successfully. A particular challenge arises because sediments are ubiquitous and mobile in karst systems and may either facilitate contaminant transport or act as long-term substrates for storage via sorption. However, electrochemical remediation is a promising technology to be optimized for karst aquifers due to easy manipulation and control of groundwater chemistry as well as low cost, ability for in situ application, and performance under alternative power sources. This study investigates the effects of suspended karst sediments on the electrochemical remediation of groundwater via electro-Fenton (EF) mechanism. The EF mechanism relies on direct electrolysis (i.e., water electrolysis and ferrous iron release) and indirect, electrochemically-induced processes (i.e., Pd catalyzed H2O2 production). These processes can be optimized for H2O2 generation and support of its activation to hydroxyl radicals - a powerful oxidant capable of degrading and transforming a wide range of contaminants (e.g., chlorinated solvents). In this study, we tested sediments varying in concentrations of Fe, Mn and buffering capacities. When the sediments were introduced into the EF experiments, there were adverse effects on the H2O2 content: at steady state (120 min), Pd catalyzed formation of H2O2 decreased by 60%, 57%, and 75% in the presence of suspended sediment collected from three separate karst locations. Presented results imply that sediments' presence influences EF mechanism in electrochemical systems, but given the flexibility of the technology, it can be optimized in terms of electrode materials, current intensities and current regimes to address these challenges.
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Sinkholes and the engineering and environmental impacts of karst : proceedings of the ... Multidisciplinary Conference on Sinkholes and the Engineering and Environmental Impacts of Karst. Multidisciplinary Conference on Sinkholes and th...
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