Matching Items (5)
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- All Subjects: disinfection byproducts
- Creators: Fox, Peter
- Status: Published
Description
Increasing concentrations of carbon dioxide in the atmosphere will inevitably lead to long-term changes in climate that can have serious consequences. Controlling anthropogenic emission of carbon dioxide into the atmosphere, however, represents a significant technological challenge. Various chemical approaches have been suggested, perhaps the most promising of these is based on electrochemical trapping of carbon dioxide using pyridine and derivatives. Optimization of this process requires a detailed understanding of the mechanisms of the reactions of reduced pyridines with carbon dioxide, which are not currently well known. This thesis describes a detailed mechanistic study of the nucleophilic and Bronsted basic properties of the radical anion of bipyridine as a model pyridine derivative, formed by one-electron reduction, with particular emphasis on the reactions with carbon dioxide. A time-resolved spectroscopic method was used to characterize the key intermediates and determine the kinetics of the reactions of the radical anion and its protonated radical form. Using a pulsed nanosecond laser, the bipyridine radical anion could be generated in-situ in less than 100 ns, which allows fast reactions to be monitored in real time. The bipyridine radical anion was found to be a very powerful one-electron donor, Bronsted base and nucleophile. It reacts by addition to the C=O bonds of ketones with a bimolecular rate constant around 1* 107 M-1 s-1. These are among the fastest nucleophilic additions that have been reported in literature. Temperature dependence studies demonstrate very low activation energies and large Arrhenius pre-exponential parameters, consistent with very high reactivity. The kinetics of E2 elimination, where the radical anion acts as a base, and SN2 substitution, where the radical anion acts as a nucleophile, are also characterized by large bimolecular rate constants in the range ca. 106 - 107 M-1 s-1. The pKa of the bipyridine radical anion was measured using a kinetic method and analysis of the data using a Marcus theory model for proton transfer. The bipyridine radical anion is found to have a pKa of 40±5 in DMSO. The reorganization energy for the proton transfer reaction was found to be 70±5 kJ/mol. The bipyridine radical anion was found to react very rapidly with carbon dioxide, with a bimolecular rate constant of 1* 108 M-1 s-1 and a small activation energy, whereas the protonated radical reacted with carbon dioxide with a rate constant that was too small to measure. The kinetic and thermodynamic data obtained in this work can be used to understand the mechanisms of the reactions of pyridines with carbon dioxide under reducing conditions.
ContributorsRanjan, Rajeev (Author) / Gould, Ian R (Thesis advisor) / Buttry, Daniel A (Thesis advisor) / Yarger, Jeff (Committee member) / Seo, Dong-Kyun (Committee member) / Arizona State University (Publisher)
Created2015
Analysis of photocatalysis for precursor removal and formation inhibition of disinfection byproducts
Description
Disinfection byproducts are the result of reactions between natural organic matter (NOM) and a disinfectant. The formation and speciation of DBP formation is largely dependent on the disinfectant used and the natural organic matter (NOM) concentration and composition. This study examined the use of photocatalysis with titanium dioxide for the oxidation and removal of DBP precursors (NOM) and the inhibition of DBP formation. Water sources were collected from various points in the treatment process, treated with photocatalysis, and chlorinated to analyze the implications on total trihalomethane (TTHM) and the five haloacetic acids (HAA5) formations. The three sub-objectives for this study included: the comparison of enhanced and standard coagulation to photocatalysis for the removal of DBP precursors; the analysis of photocatalysis and characterization of organic matter using size exclusion chromatography and fluorescence spectroscopy and excitation-emission matrices; and the analysis of photocatalysis before GAC filtration. There were consistencies in the trends for each objective including reduced DBP precursors, measured as dissolved organic carbon DOC concentration and UV absorbance at 254 nm. Both of these parameters decreased with increased photocatalytic treatment and could be due in part to the adsorption to as well as the oxidation of NOM on the TiO2 surface. This resulted in lower THM and HAA concentrations at Medium and High photocatalytic treatment levels. However, at No UV exposure and Low photocatalytic treatment levels where oxidation reactions were inherently incomplete, there was an increase in THM and HAA formation potential, in most cases being significantly greater than those found in the raw water or Control samples. The size exclusion chromatography (SEC) results suggest that photocatalysis preferentially degrades the higher molecular mass fraction of NOM releasing lower molecular mass (LMM) compounds that have not been completely oxidized. The molecular weight distributions could explain the THM and HAA formation potentials that decreased at the No UV exposure samples but increased at Low photocatalytic treatment levels. The use of photocatalysis before GAC adsorption appears to increase bed life of the contactors; however, higher photocatalytic treatment levels have been shown to completely mineralize NOM and would therefore not require additional GAC adsorption after photocatalysis.
ContributorsDaugherty, Erin (Author) / Abbaszadegan, Morteza (Thesis advisor) / Fox, Peter (Committee member) / Mayer, Brooke (Committee member) / Arizona State University (Publisher)
Created2011
Description
Local municipalities in the Phoenix Metropolitan Area have voiced an interest in purchasing alternate source water with lower DBP precursors. Along the primary source is a hydroelectric dam in which water will be diverted from. This project is an assessment of optimizing the potential blends of source water to a water treatment plant in an effort to enable them to more readily meet DBP regulations. To perform this analysis existing water treatment models were used in conjunction with historic water quality sampling data to predict chemical usage necessary to meet DBP regulations. A retrospective analysis was performed for the summer months of 2007 regarding potential for the WTP to reduce cost through optimizing the source water by an average of 30% over the four-month period, accumulating to overall treatment savings of $154 per MG ($82 per AF).
ContributorsRice, Jacelyn (Author) / Westerhoff, Paul (Thesis advisor) / Fox, Peter (Committee member) / Hristovski, Kiril (Committee member) / Arizona State University (Publisher)
Created2011
Description
Granular activated carbon (GAC) is effectively used to remove natural organic matter (NOM) and to assist in the removal of disinfection byproducts (DBPs) and their precursors. However, operation of GAC is cost- and labor-intensive due to frequent media replacement. Optimizing the use of GAC is necessary to ensure treatment efficiency while reducing costs. This dissertation presents four strategies to reduce improve GAC usage while reducing formation of DBPs. The first part of this work adopts Rapid Small Scale Tests (RSSCTs) to evaluate removal of molecular weight fractions of NOM, characterized using size exclusion chromatography (SECDOC). Total trihalomethanes (TTHM), haloacetic acids (HAA5) and haloacetonitriles (HAN) formation were quantified after treatment with GAC. Low MW NOM was removed preferentially in the early bed volumes, up until exhaustion of available adsorption sites. DBP formation potential lowered with DOC removal. Chlorination prior to GAC is investigated in the second part of this work as a strategy to increase removal of NOM and DBP precursors. Results showed lower TTHM formation in the effluent of the GAC treatment when pre-chlorination was adopted, meaning this strategy could help optimize and extend the bed life if GAC filters. The third part of this work investigates in-situ GAC regeneration as an alternative to recover adsorption capacity of field-spent GAC that could potentially offer new modes of operation for water treatment facilities while savng costs with reactivation of spent GAC in an external facility. Field-spent GACs were treated with different oxidant solutions and recovery in adsorption capacity was evaluated for NOM and for two micro pollutants. Recovery of GAC adsorption capacity was not satisfactory for most of conditions evaluated. This indicates that in-situ GAC regeneration could be more effective when the adsorbates are present at high concentrations. Lastly, this work investigates the impact of low molecular weight polyDADMAC on N-nitrosodimethylamine (NDMA) formation. Water treatment facilities rely on polyDADMAC as a coagulant aid to comply with NOM removal and turbidity requirements. Since polymer-derived NDMA precursors are not removed by GAC, it is essential to optimize the use and synthesis of polyDADMAC to reduce NDMA precursors during water treatment.
ContributorsFischer, Natalia (Author) / Westerhoff, Paul (Thesis advisor) / Hristovski, Kiril (Committee member) / Fox, Peter (Committee member) / Arizona State University (Publisher)
Created2017
Description
Carbon dioxide (CO2) is one of the most dangerous greenhouse gas. Its concentration in the atmosphere has increased to very high levels since the industrial revolution. This continues to be a threat due to increasing energy demands. 60% of the worlds global emissions come from automobiles and other such moving sources. Hence, to stay within safe limits, it is extremely important to curb current emissions and remove those which have already been emitted. Out of many available technologies, one such technology is the moisture swing based air capture technology that makes use of resin material that absorbs CO2 when it is dry and releases it when it is wet. A mathematical model was developed to better understand the mechanism of this process. In order to validate this model, numerical simulation and experimentation was done. Once the mechanism was proved, it was seen that there are many factors and parameters that govern this process. Some of these do not have definite value. To find the best fit value for these parameters, an optimized fitting routine needs to be developed that can minimize the standard deviation of the error. This thesis looks into ways in which the optimization of parameters can be done and the possible future work by using substantial data.
ContributorsChopra, Vinuta (Author) / Lackner, Klaus S (Thesis advisor) / Fox, Peter (Committee member) / Wright, Allen (Committee member) / Arizona State University (Publisher)
Created2016