Organically modified low-grade kaolin as a secondary containment material for underground storage tanks

Batch scale reactions were conducted to evaluate the efficacy of modified low-grade kaolin for the treatment of petroleum contaminants. Low-grade kaolin, which has been unvalued as material in the mining process because of its low quality for commercial products, was modified with HDTMA (hexadecyl-trimethylammonium), and its efficiency was compared with that of HDTMA-modified bentonite, which is used as a secondary containment barrier for underground storage tanks. The sorption capacity and hydraulic conductivity of both the HDTMA-modified bentonite and low-grade kaolin were investigated and showed distribution coefficients in the sorption of benzene, toluene, ethylbenzene and xylene ranging between 45.7 and 583.7 and 57.0 and 525.1, respectively. The hydraulic conductivities were 2.53 × 10⁻⁸ and 5.62 × 10⁻⁸ cm/s for the HDTMA-modified bentonite and low-grade kaolin, respectively. These results suggest that HDTMA-modified low-grade kaolin could be used as a hydraulic barrier against advection migration of petroleum contaminants. Simulation of the one-dimensional transport of benzene through a liner made of either one of the compounds was also performed. These results also showed that HDTMA-modified kaolin more effectively retards the transport of benzene.     

One-at-a-time sensitivity analysis of pollutant loadings to subsurface properties for the assessment of soil and groundwater pollution potential

Chemical leak was numerically simulated for four chemical substances: benzene (light non-aqueous phase liquid (NAPL)), tetrachloroethylene (dense NAPL), phenol (soluble in water), and pentachlorophenol (white crystalline solid) in a hypothetical subsurface leak situation using a multiphase compositional transport model. One metric ton of chemical substances was assumed to leak at a point 3.51 m above the water table in a homogeneous unconfined aquifer which had the depth to water table of 7.135 m, the hydraulic gradient of 0.00097, the recharge rate of 0.7 mm/day, and the permeability of 2.92?×?10^?10 m². For comparison, surface spill scenarios, which had a long pathway from source to the water table, were simulated. Using the model results, point-source pollutant loadings to soil and groundwater were calculated by multiplying mass, impact area, and duration above and below the water table respectively. Their sensitivity to subsurface properties (depth to water table, recharge rate, porosity, organic carbon content, decay rate, hydraulic gradient, capillary pressure, relative permeability, permeability) was analyzed, with changing each parameter within acceptable ranges. The study result showed that the pollutant loading to groundwater was more sensitive to the subsurface properties than the pollutant loading to soil. Decay rate, groundwater depth, hydraulic gradient and porosity were influential to pollutant loadings. The impact of influential parameters on pollutant loadings was nonlinear. The dominant subsurface properties of pollution loadings (e.g., decay rate, groundwater depth, hydraulic gradient, and porosity for groundwater) also affect the vulnerability, and the subsurface pollutant loadings defined in this study are dependent on chemical properties as well, which indicates that the influential hydrogeological and physicochemical parameters to pollutant loadings can be used for pollution potential assessment. The contribution of this work is the suggestion that the sensitivity of pollutant loadings can be used for pollution potential assessment. Soil and groundwater pollution potential of chemicals are discussed altogether for leak scenarios. A physics-based model is used to understand the impact of subsurface properties on the fate and transport of chemicals above and below the water table, and consequently their impact on the pollutant loading to soil and groundwater.

     

Effects of SO<Subscript>2</Subscript> contamination on rising CO<Subscript>2</Subscript> drops under high pressure

Although the flow dynamics of pure liquid drops in other liquids has been well researched, little attention has been paid to the impacts of impurities. Hence, most of research is not directly applicable to the real world. To address this gap, we conducted numerical experiments simulating the rise of pure and contaminated drops. It was selected to study liquid CO₂ drops contaminated with SO₂ under high pressure because such mixtures mimic potential scenarios in which drops may leak from carbon capture and storage (CCS) facilities or pipelines. First, numerical simulation experiments were performed to validate our method by comparing our results with previous research on pure drops. Second, the validated numerical approach was applied to simulations of contaminated drops to investigate how contaminants affect rising drops. The results show that the SO₂ contamination caused changes in deformation, breakup phenomena, rising velocities, surrounding flow fields and drag coefficients. Most importantly, the contamination resulted in the formation of smaller “child drops”; such breakup is not observed in pure CO₂ drops. The formation of child drops in turn affects the streamlines, patterns and areas of wakes behind the contaminated drops. The addition of contaminants also enhances the dissolution rate, which is affected by the contaminant concentration and by the flow dynamics of the rising drop. Our results would improve understanding the rise of impure CO₂ drops, such as drops potentially leaked by future CCS operations.     

Manganese and iron oxide immobilized activated carbons precursor to dead biomasses in the remediation of cadmium-contaminated waters

The aim of the present investigation was to exploit the high specific surface area of activated carbons in immobilizing the manganese and iron oxides as to obtain a suitable, efficient and cost effective and environment benign wastewater treatment process in the remediation of cadmium-contaminated waters. The manganese and iron oxides were impregnated in situ onto the surface and pores of the activated carbons precursors to the rice hulls and areca nut wastes. The solids were characterized with the help of Fourier transform infrared spectroscopy and X-ray diffraction analytical data, and the BET specific surface area as obtained. The surface morphology of these solids was discussed with the help of scanning electron microscopic images. The activated carbon samples along with the manganese and iron immobilized activated carbons were further employed in the batch and column reactor operations in the remediation of cadmium-contaminated waters. The batch data showed that an increase in sorptive pH from 2.0 to 10.0 and concentration from 1.0 to 20 mg/L favoured the uptake of cadmium by these solids. Moreover, the 1,000 times increase in background electrolyte concentrations NaNO₃ caused an insignificant decrease in cadmium uptake by these solids, which inferred that sorbing ions/species were sorbed specifically and forming ‘inner-sphere’ complexes onto the solid surface. The concentration dependence data were utilized to model various adsorption isotherms and indicated that Freundlich adsorption isotherm was reasonably fitted well. The kinetic data was fitted well to the pseudo-second-order rate equations; hence, the equilibrium sorption capacity was estimated. Furthermore, the dynamic experiments carried out by the column experiments and the breakthrough data were fitted well to the non-linear Thomas equations; accordingly, the loading capacity of the column was estimated. Iron or manganese immobilized activated carbons showed relatively higher loading capacity compared to its precursor activated carbons hence showing its possible implication in the remediation processes. Moreover, among these modified ACs, IIAC showed higher removal capacity than the MIAC solid.     

Evaluation of Lake Modification Alternatives for Lake Sihwa, Korea

After the construction of an embankment at the Bay of Sihwa in Korea, a lake of 56.5 km² surface area and 330 million m³ volume was created. Because of rapid socioenvironmental changes and the lowering of water quality in Lake Sihwa, various external measures have been proposed and some of them are being implemented. In this paper, we examine two alternatives for in-lake modification: one alternative is zoning of the lake by constructing two submerged dams and the other is channeling of the lake through reclamation. Water quality modeling was conducted for both alternatives to assess their effects. Results of the modeling revealed that the reduction of the lake size through two different approaches, when accompanied with other external measures, would improve the water quality, but to different degrees. The zonation is expected to improve the freshwater quality up to the level supplying 45 million m³ of water per year for agricultural use. The quality of channeled water would be inappropriate for agricultural use, but suitable for outdoor activities such as recreation or fishing regardless of reclamation plans considered.     

Removal of mixed contaminants by Fe0-based biobarrier in flow-through columns using recycled waste materials

The present study investigated the reactivity and ability of permeable reactive barriers [zero-valent iron (ZVI)-barrier plus biobarrier) to remove various contaminants (Cd, As, Zn, Cu, Mn, Cr, NO₃ ⁻, NH₄ ⁺, and COD_cr) from synthetic leachate. Two different reactive materials were used in this study, namely ZVI and autoclaved lightweight concrete (ALC). After 90 days of column operation, the contaminant profiles were determined along the length of the columns. The heavy metals were extensively removed in the bio-ALC and sequential barriers (ZVI plus bio-ALC), however the removal efficiencies for the heavy metals Zn and Cr in the ALC and bio-ALC barriers were comparatively low. Nitrate was completely removed (>99.9%) in the ALC, bio-ALC, and sequential barriers. More than 50% of the produced ammonium and organic materials were removed in the biologically reactive zone of the sequential barriers. The results of the present study suggest that sequential barriers are one of the best solutions for in situ remediation and that they can be applied to clean up the leachate released from landfills.