Bibliography - P. R. Jaffé

1. Wang, S., and P. R. Jaffé, 2004: Dissolution of Mineral Phase in Potable Aquifers due to CO₂ Releases from Deep Formations, effect of dissolution kinetics. Energy Conversion and Management, 45(18-19), doi:10.1016/j.enconman.2004.01.002 2838-2848
   [ Abstract ]

   Injection of supercritical CO₂ into deep saline aquifers is a technique for sequestration of large amounts of CO₂ that is currently being investigated as a means to ameliorate the release of greenhouse gases into the atmosphere. Because complete characterization of these geological formations is not possible, the likelihood that some fraction of the injected CO₂ will leak into overlying aquifers needs to be considered. If the leaking CO₂ were to reach shallow groundwater aquifers, it could lead to geochemical alterations with detrimental effects on the water quality of these potable aquifers. Identification and assessment of these effects is necessary to analyze risks associated with geologic sequestration of CO₂ adequately. In order to assess if there is a potential of solubilizing trace metals, metalloids and/or selected radionuclides by CO₂ releases from deep formations into potable aquifers, a series of simulations were conducted. Numerical simulations were conducted for a series of CO₂ release scenarios and different aquifer geochemical properties. The effect of CO₂ induced pH changes as well as trace metal solubilization was assessed using a geochemical transport model. Results show that elevated CO₂ levels in freshwater aquifers can enhance the dissolution of trace metals so that concentrations may reach undesirable levels at the local scale. Transport models demonstrate the importance of assessing the areal extent of this CO₂ release, as well as the need to gain thorough understanding of the key kinetic processes related to CO₂ solubilization and the dissolution of a trace metal containing mineral phase.

2. Jaffé, P. R., and S. Wang, October 2003: Potential Effect of CO₂ releases from deep reservoirs on the quality of freshwater aquifers. Proceedings of the 6th International Conference on Greenhouse Gas Control Technologies (GHGT-6), 1657-1660
   [ Abstract ]

   Injection of supercritical CO₂ into deep saline aquifers is a promising technique for sequestration of large amounts of CO₂. If some fraction of the injected CO₂ were to leak and reach shallow groundwater aquifers, it would lead to geochemical alterations that could have detrimental effects on the water quality. A mathematical model was developed to simulate the change in solution pH and the enhanced dissolution of trace metals as carbon dioxide dissolves into the groundwater. The model takes into account the buffering capacity as different mineral phases dissolved into the aqueous phase and includes the dissolution of minerals with the concomitant increase in dissolved species in the aqueous phase. A series of simulations were conducted for various CO₂ release scenarios and different aquifer properties. Results show that CO₂ dissolution in poorly buffered aquifers can solubilize trace metals to levels that exceed drinking water standards. This approach allows for a reasonable assessment of the risks on the quality of freshwater aquifers due to the escape of CO₂ from deep geological formations.

3. Wang, S., P. R. Jaffé, G. Li, S. W. Wang, and H. A. Rabitz, 2003: Simulating Bioremediation of Uranium-Contaminated Aquifers; Uncertainty Assessments of Model Parameters. Journal of Contaminant Hydrology, 64(3-4), doi:10.1016/S0169-7722(02)00230-9 283-307
   [ Abstract ]

   Bioremediation of trace metals and radionuclides in groundwater may require the manipulation of redox conditions via the injection of a carbon source. For example, after nitrate has been reduced, soluble U(VI) can be reduced simultaneously with other electron acceptors such as Fe(III) or sulfate to U(IV), which may precipitate as a solid (uraninite). To simulate the numerous biogeochemical processes that will occur during the bioremediation of trace-metal-contaminated aquifers, a time-dependent one-dimensional reactive transport model has been developed. The model consists of a set of coupled mass balance equations, accounting for advection, hydrodynamic dispersion, and a kinetic formulation of the biological or chemical transformations affecting an organic substrate, electron acceptors, corresponding reduced species, and trace metal contaminants of interest, uranium in this study. This set of equations is solved numerically, using a finite difference approximation. The redox conditions of the domain are characterized by estimating the pE, based on the concentration of the dominant terminal electron acceptor and its corresponding reduced species. This pE and the concentrations of relevant species are then used by a modified version of MINTEQA2, which calculates the speciation/sorption and precipitation/ dissolution of the species of interest under equilibrium conditions. Kinetics of precipitation/ dissolution processes are described as being proportional to the difference between the actual and calculated equilibrium concentration. A global uncertainty assessment, determined by Random Sampling High Dimensional Model Representation (RS-HDMR), was performed to attain a phenomenological understanding of the origins of output variability and to suggest input parameter refinements as well as to provide guidance for field experiments to improve the quality of the model predictions. By decomposing the model output variance into its different input contributions, RSHDMR can identify the model inputs with the most influence on various model outputs, as well as their behavior pattern on the model output. Simulations are performed to illustrate the effect of biostimulation on the fate of uranium in a saturated aquifer, and to identify the key processes that need to be characterized with the highest accuracy prior to designing a uranium bioremediation scheme.

4. Brown, D. G., and P. R. Jaffé, 2001: Effects of Nonionic Surfactants on Bacterial Transport Through Porous Media. Environmental Science and Technology, 35(19), doi:10.1021/es010577w 3877-3883
   [ Abstract ]

   Nonionic surfactants of the form C_xE_y, where x is the number of carbons in the alkyl chain and y is the number of ethylene oxide units in the polyoxyethylene (POE) chain, were studied for their ability to alter the transport of Sphingomonas pacilimobilis through an aquifer sand. The surfactants C₁₂E₄ (Brij 30) and C₁₂E₂₃ (Brij 35) were the focus of this study. Through a systematic study, it was shown that these nonionic surfactants were able to enhance the transport of this bacterial culture through porous media. The magnitude of the enhancement increased with decreasing solution ionic strength and increasing POE chain length. The mechanism of this enhanced transport appears to be due to expansion of the electric double layer about the bacteria and aquifer sand through displacement of the counterions by the sorbed surfactant. This expanded electric double layer increases the electrostatic repulsion, with a resultant reduction in the collision efficiency and an increase in the Langmuirian blocking parameter. Application of the colloid filtration theory with the experimental parameters of this study shows that nonionic surfactants have the potential to significantly enhance the bacterial travel distance, especially for low ionic strength systems.

5. Brown, D. G., and P. R. Jaffé, 2001: Effects of Nonionic Surfactants on the UV/Visible Absorption of Bacterial Cells. Biotechnology and Bioengineering, 74(6), doi:10.1002/bit.1138 476-482
   [ Abstract ]

   Nonionic surfactants are used in a number of different microbiological applications, including solubilization of cell membranes, washing bacterial cultures prior to experimentation, and enhancing biodegradation of low-solubility compounds. An important consideration in these applications is the potential for the surfactant to alter the cell membrane. One potential means to monitor the impact of surfactants on the bacterial cell membrane is through monitoring the absorbance spectrum of the bacterial suspension. This is due to the colloidal nature of bacteria, where the absorbance of a bacterial suspension is related to the size and refractive index of the bacterial cells. Through a systematic study it was shown that there can be a significant change in the bacterial absorbance spectrum due to the presence of nonionic surfactants, with the effect a function of surfactant structure and concentration, solution ionic strength and cation valence. The effects were most pronounced with Na+ as the cation, with surfactants having midrange hydrophile-lipophile balance (HLB) values, and with surfactant concentrations above the CMC. The results indicate that measurement of the absorbance spectrum of bacterial cultures can provide a means to monitor the effects of nonionic surfactants on the bacterial cell membrane. In addition, depending on the specific application, appropriate selection of surfactant structure and media composition can be made to enhance or minimize the effects.

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