Yuzhou Li, Chemistry Department, mentor
In Situ Metal Removal in Chemical Mechanical Polishing
The use of an ion exchange resin to remove copper ions from chemical mechanical polishing (CMP) waste stream during the polishing process has been investigated. Complexation experiments were employed to determine the most efficient resins in removing copper ions from a cupric nitrate solution. The concentration of copper ions in the cupric nitrate solution mirrored industrial process concentrations. An HP Diode Array Spectrophotometer was used to determine the efficiency of each resin in removing copper from solution. Two of the five resins tested reduced the concentration of copper ions significantly. In addition, there was a direct correlation between the amount of resin added and the amount of copper ions removed from solution. The two ion exchange resins that produced the most favorable results were DowexÒ M-43 and DowexÒ M-4195. Finally, DowexÒ M-4195 was introduced into the polishing slurry. Preliminary in situ polishing data revealed that DowexÒ M-4195 did exchange an average of 65.4% of copper ions produced during the polishing run. In addition, the removal rate of copper was not affected by the presence of the resin during the in situ process.
The use of the polydentate ligands sodium citrate, Amine-14, and pyrogallol as chelating agents for tantalum has also been investigated. Each ligand was added to the polishing slurry at 1, 3, and 5 wt %. All other polishing parameters remained the same throughout the process. Analysis of polishing data reveals that the copper to tantalum selectivity with the use of pyrogallol was 3.8 to 1. For sodium citrate the selectivity was 4.7 to 1 and for Amine-14 the selectivity was 5.8 to 1. This data reveals that the addition of these chelating agents slightly increased the removal rate of tantalum. In addition, the polish rate of copper was not affected by the presence of these ligands in the polishing slurry.
Barry K. Lavine, Chemistry Department, mentor
HPLC of Priority Pollutants using Secondary Chemical Equilibria,
Cyclodextrin is a cylinder shaped molecule with an axial void cavity. Although its outer surface is hydrophilic, its inner cavity is apolar in character. Aromatic compounds such as benzene and toluene can form inclusion complexes with cyclodextrin when it is used as an organic modifier in the mobile phase. Marked sensitivity improvements in fluorescence detection result from employing cyclodextrin aqueous mobile phase modifers. Cyclodextrin mobile phase modifiers will also improve the selectivity of a separation due to the introduction of secondary chemical equilibria into the chromatographic system. However, band broadening is a serious problem, limiting the utility of this technique. The source and a possible remedy for band broadening in cyclodextrin mediated HPLC will be discussed.
Ortho-nitrotoluene and meta-nitrotoluene showed trends of decreasing plate count and increasing asymmetry when cyclodextrin was added to the mobile phase with a cyanopropyl column. Therefore, a loss in column efficiency occurred when cyclodextrin was added to the mobile phase. For the phenyl column, the plate count increased and asymmetry decreased with the addition of cyclodextrin, which suggests that a loss of efficiency did not occur.
Para-nitrotoluene was a more complex case. It showed the opposite trends with respect to the other two compounds. At this time, it is not known why the p-nitrotoluene did not follow the behavior of the other 2 nitrotoluene isomers.
The results of the experiments involving o-nitrotoluene and m-nitrotoluene isomers support the hypothesis that changes in mass transfer kinetics due to the introduction of cyclodextrin in the mobile phase will not occur when phenyl bonded phases are used. However, changes in the kinetics of solute mass transfer do occur when a cyanopropyl bonded phase column is used in tandem with a cyclodextrin mobile phase. Nevertheless, further experiments using a variety of retention probes are necessary to elucidate the phenomena. Furthermore, computer models detailing the effect of SCE on N would also prove beneficial since it would be possible to benchmark efficiency measurements with theoretical calculations that assume complete equilibria within the column.
Stefan Grimberg, Civil and Environmental Engineering,
Conditions that Affect Adhesive Forces and Microbial Interactions in Contaminated Subsurface Systems: A Study of the Electrostatic Force
An understanding of the adhesive forces of bacteria in contaminated subsurface systems is crucial to understanding the role microbes play within the system and in processes such as bioremediation and transport of contaminants. This study measured the effect of physiological state and surrounding environment on one type of adhesive force, electrostatic, for Pseudomonas sacrophilia (P15), Pseudomonas stutzeri (P16), and Acinebacter calcoaceticus (RAG1). The electrostatic force was measured over the growth phase for each species to ascertain the effect of physiological state on the electrostatic force, and two nitrogen concentrations and three different carbon sources were used to ascertain the effect of the surrounding environment on the electrostatic force. Electrophoretic mobility of the cell was used to quantify the strength of the electrostatic force for each cell, and the zeta potential of the cell was found using these values. A significant change in the zeta potential over the growth phase was seen for RAG1 although no significant change was determined for P15 or P16. A significant decrease in the zeta potential for the higher concentration of nitrogen was observed for all bacterial cultures during the late exponential growth phase. Each species reacted differently to the different carbon sources.
Stefan Grimberg, Civil and Environmental Engineering,
Forces of Adhesion Affecting
Microbial Interactions in Contaminated Subsurface Systems: A Study of
An understanding of the adhesive forces of bacteria in contaminated subsurface systems is crucial to understanding the role microbes play within systems and in processes such as bioremediation. The forces affecting microbial adhesion are determined by the cell's surface and are a function of the physiological state of the cell as well as its surrounding environment. Under the extended DLVO (Derjaguin, Landau, Verwey, and Overbeek) theory hydrophobic forces are defined as one force affecting the adhesive properties of cells. Hydrophobic forces were measured throughout the growth phase for Pseudomonas stutzeri (P16), Pseudomonas sacrophilia (P15), and Acinebacter calcoaceticus (RAG1). Variations of two nitrogen concentrations and three different carbon sources provided a matrix to measure the impact of different environments.
Hydrophobic forces were quantified by contact angle measurements on a filtered lawn of bacteria. Under van Oss's model van der Waals and acid-base interaction components of hydrophobic forces were calculated. The nonpolar energy of interaction, a measure of hydrophobicity between two particles in water, was calculated as a function of the acid/base components. The energy of interaction between two bacteria can be used to infer something about the adhesion of bacteria to a hydrocarbon pollutant. A significant change in the free energy of interaction was seen over the growth phase for RAG-1 and P16. A change in the energy of interaction was observed for different nitrogen concentrations for all tested bacteria. When grown under conditions with ten times the concentration of nitrogen the bacterial cells became less hydrophobic. Bacterial cells for strains P15, P16, and RAG1 were more hydrophobic when grown on coal tar than on carbon rich media and glucose. The change in hydrophobicity with changes in carbon source were caused by a soluble compound on the bacterial cells.
Susan E. Powers, Civil and Environmental Engineering,
The Effect of DNAPL-Quartz Electrostatic Attraction on Wettability Alteration
The study of DNAPLs, such as crude oil and creosote, and their relationship to subsurface porous media has evolved in the fields of both petroleum and environmental engineering. One of the defining characteristics of the relationship between DNAPLs, water, and the porous media is wettability. Wettability is the preference in a liquid-liquid-solid system for one liquid to coat the solid. Although wettability had been largely overlooked in modeling and field work (Cohen and Mercer 1993), recent research has been performed to attempt to define the factors influencing wettability and wettability changes in subsurface systems (Powers et al. 1996; Buckley et al. 1997; Barranco and Dawson 1999).
In a multi-phase system with DNAPL, water, and mineral components, the charge at the DNAPL-water interface has been observed to change with respect to pH. It has also been found that wettability in DNAPL systems is highly dependent on pH due to the presence of surface-active compounds at the DNAPL-water and DNAPL-solid interfaces (Buckley et al. 1989).
It was hypothesized that the electrostatic attraction between the DNAPL and the solid surfaces alone provided for a clear and accurate description of the process of wettability change. This hypothesis was tested by determining the charge of the DNAPL-water and the mineral-water interfaces at different pH values. Throughout ranges of opposite charges on the DNAPL-water and mineral-water interfaces, electrostatic attraction was assumed to be occurring. Conversely, when the charges on the interfaces were the same, electrostatic repulsion was assumed to be occurring.
In order to determine the wettability characteristics of the system, adhesion tests were performed. These tests were carefully controlled to reduce the influence of confounding factors such as DNAPL-water interfacial film formation and DNAPL wetting of needle. Adhesion tests were completed for one creosote and two coal tar samples over a range of environmentally realistic pH values to find the transition from oil to water-wetting.
The adhesion tests provided data that indicate that the electrostatic attraction between the DNAPL and solid surfaces is not the only factor in changing wettability. The wettability change from oil-wetting conditions occurred in all samples at values that were more than 0.5 pH units above the DNAPL Point of Zero Charge and was followed by an extended intermediate-wetting phase before finally reaching a water-wetting condition. The experimental data suggests that although electrostatic attraction most likely plays an important role in wettability change, other factors contribute to the overall change from water-wetting to oil-wetting conditions.
The Effect of Temperature Gradients on the Residence Time Distribution in Water Treatment Processes
The residence time of water in a reactor is of primary importance to any water treatment process. This parameter is mathematically defined as the quotient of the reactor volume and the flow rate. However, incomplete mixing as well as the presence of dead spaces in the reactor do not allow the calculation of the residence time by this simple formula. Therefore, one must evaluate this parameter through the generation of an experimental residence time distribution function.
Temperature gradients are thought to have an important effect on the residence time distribution function. The slight density changes in water between the temperatures of 0-20oC are attributed to the buoyancy effect observed as the influent enters the reactor. As a result, the water streamlines vary depending on the temperature of the water entering the tank.
In order to study this buoyancy effect, a bench scale model based on the Canton Water Treatment Plant was used. By means of positive and negative tracer studies and spectrophotometer analysis, experiments were conducted to predict the behavior of an actual reactor. The buoyancy effect caused by the temperature gradients was simulated by the addition of sodium chloride to the influent or the reactor as needed.
The tracer studies conducted have shown that for the particular reactor used in the experiments, the residence time significantly decreases when the influent is denser than the fluid in the tank. This effect can also be clearly seen in the nature of the mathematical model(s) used to fit the resulting curves.
Possible engineering solutions to the problem posed by temperature gradients are examined. This paper also contains a brief discussion of the importance of the densimetric Froude number in understanding the hydrodynamics of this phenomenon.
Thomas C. Young, Civil and Environmental Engineering, mentor
Fate Of Free Cyanide In Surface Waters.
Cyanide is a by-product of the aluminum smelting process and has been found in surface waters near aluminum plants. Most of the cyanide is present in the form of stable metal complexes (e.g. Fe(CN)63-) which do not exhibit environmental toxicity. However, these complexes can undergo a series of reactions that release CN- and HCN, the two forms of toxic free cyanide. The photolysis of the metal complex releases CN-, which is protonated to produce HCN. HCN is a gas which volatilizes at a rate that is dependent on aquatic conditions, including temperature and pH. In this study we examine one factor that determines the rate of volatilization.
The mass transfer velocity of the volatilization reaction depends on the Henry’s law constant (kH) for HCN. Currently, estimates of the value for this constant are not widely available in the literature. To measure kH we designed a closed system containing air and water of known CN- concentration. The system was allowed to reach equilibrium, at which time the pH and total aqueous CN- concentration were measured. Using mass balances and the acid dissociation equation for HCN (pKA = 9.31), the amount of HCN in each phase was determined. kH was calculated as the ratio of the partial pressure to the aqueous molar concentration of HCN. A total of 26 experimental trials were conducted, which yielded a mean value of 3.07 ± 0.36 atm-L/mol (mean ± Standard Error) for the kH of HCN under ambient laboratory conditions (23 oC, 1 atm). Estimates of kH found in the literature compare favorably with this value. The results of this study provide a measure of the uncertainty associated with the value of kH for HCN.
Thomas L. Theis, Civil and Environmental Engineering, mentor
The Revision of a Groundwater Treatment Cost Analysis Model
In the early 1980’s, Baltimore Gas and Electric Company
(BG & E) discovered a large plume of oil below their Spring Gardens
Facility. The plume of oil was 10 to 15
feet below the surface, yet was above the ground water. Due to the close proximity to the
In 1994, Clarkson Graduate student Dennis O’Carroll developed the Groundwater Oil Reduction Diagnostic Optimizer (GORDO), which is a computer program that models the Spring Gardens Oil Recovery Facility, and outputs the unit costs for different input parameter test cases. After the GORDO program was completed and presented to BG & E, there were several calibrations and alterations to be made on the program. The objective of this continual work on the GORDO is to address the issues presented by BG & E, by incorporating a present value analysis in the program, as well as calibrating the oil recovery curve and the efficiency of the unit processes.
The present value analysis was incorporated into the GORDO program, and it inputs several different ground water pumping rates, as well as many variables, and outputs the plant life and present value cost for the different pumping rates. The optimal case also outputs the present value costs for the different unit processes.
Several calibrations of the assumed workings of the plant were also calibrated to the particular plant. This was done by analyzing data directly from the plant, which ranged from the daily logs of the water and oil pumped for the different wells, to results of tests for different chemicals in the water. This data was analyzed to find the relationship between the water pumping rate and the oil recovery rate, and the efficiency of the different unit processes.
Thomas M. Holsen, Civil and Environmental
Particle and Gas Phase
Sulfate and Nitrate Dry Deposition near the
The wet and dry atmospheric deposition of sulfates and nitrates onto the surface of the earth is considered to be one of the primary causes of acidification in natural water bodies. Traditionally, dry deposition has been difficult to measure directly, and various models assuming deposition velocities have been used. These models have not been validated; therefore, direct methods of measurement are needed, as are actual dry deposition measurements in a variety of environments.
this project, surrogate surfaces were used to measure dry deposition fluxes of
sulfates and nitrates in
show that the WSS often measured negative or small fluxes of both the sulfates
and nitrates. The negative fluxes may
have been due to possible leakage or flushing of the water surface or a
reaction between the dissolved ions and our disinfectant, mercuric chloride, or
other extraneous substances not seen in
Due to the minimal amount of time available for this project, many additional samples are needed before conclusive results can be drawn concerning dry deposition in this area, and further development of the surrogate surfaces is needed, especially the water surface sampler.
Thomas L. Theis, Civil and Environmental Engineering, mentor
The Removal of Inorganic Cyanides from Water by Ion Exchange
Many industries produce electroplating wastes composed of metal cyanide complexes. In the presence of sunlight, some metal cyanide complexes photolyze into free cyanide, HCN at acidic pH and CN- in basic pH. Cyanide (CN) concentrations in excess of 10 ug/L as CN are dangerous to aqueous ecosystems and the EPA drinking water standard for cyanide is 200 ug/L. Concentrations higher than 1 mg/L are most often treated with ozonation and oxidation; however, there are not many methods that remove dilute concentrations of cyanides. One such technology of interest is the ion exchange method.
An anion-exchange resin has been utilized as the medium of removing inorganic cyanides. The three main methods to determine cyanide concentrations after ion exchange were by total distillation for total cyanide, ion chromatography (IC) for metal-cyanides, and microdiffusion for free CN. In a timed batch system, potassium cyanide (KCN) and potassium ferrocyanide (K4Fe(CN)6) in solution, approximately 400 to 200 ug/L and 2000 to 40 ug/L as CN, respectively, were taken up by the resin within one minute of contact. Then experiments were done in an ion exchange column. In two parallel experiments, 100 and 1000 ug/L of KCN as CN were put through ion exchange resin columns, each attaining effluent containing about 4 ug/L CN. In a volumetric analysis, the resin reduced KCN concentrations from 100 to less than 10 ug/L and K4Fe(CN)6 from 100 to less than 40 ug/L as CN. The removal of KCN alone was reduced from 200 to less than 4 ug/L as CN; the removal of the iron cyanide complex alone was reduced from 200 ug/L to concentrations less than 8 ug/L. Future research is looking toward the separation of inorganic (anions) cyanides from organic (neutral charge) cyanides from water as well.
George Gilchrist, Biology, mentor
Reconstructing an invasion: interspecific competition between North American Drosophila pseudoobscura, and three populations of European D. subobscura
the late 1970’s the
Jim Thorp, Biology, mentor
Migration in the Main Channel and Backwater Areas of the
Migration in zooplankton has been demonstrated in lentic or lake systems. This phenomenon known as vertical migration usually has the zooplankton moving down to lower depths by day and moving up to the surface water at night. The movement appears to be a triggered by light intensity and is a predator avoidance adaptation. The objective of this study is to determine if zooplankton migration also occurs in lotic or riverine systems. If migration occurs in riverine systems and is not accounted for, estimation of ecosystem productivity could be biased by when and where the zooplankton sample is collected.
were taken at four different bays on the
Copepods are strong swimmers and are venerable to predation. This information combined with our results, suggests that they are hiding from predators during the day and move out into the pelagic zone to feed at night. Nauplii are relatively poor swimmers and their densities were not different between day & night suggesting no migration. However, Nauplii densities were depressed in between the bay and main channel suggesting that they are being entrained into the main channel.