Matching Items (7)
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- All Subjects: Water
- Creators: Westerhoff, Paul
Description
Nitrate is the most prevalent water pollutant limiting the use of groundwater as a potable water source. The overarching goal of this dissertation was to leverage advances in nanotechnology to improve nitrate photocatalysis and transition treatment to the full-scale. The research objectives were to (1) examine commercial and synthesized photocatalysts, (2) determine the effect of water quality parameters (e.g., pH), (3) conduct responsible engineering by ensuring detection methods were in place for novel materials, and (4) develop a conceptual framework for designing nitrate-specific photocatalysts. The key issues for implementing photocatalysis for nitrate drinking water treatment were efficient nitrate removal at neutral pH and by-product selectivity toward nitrogen gases, rather than by-products that pose a human health concern (e.g., nitrite). Photocatalytic nitrate reduction was found to follow a series of proton-coupled electron transfers. The nitrate reduction rate was limited by the electron-hole recombination rate, and the addition of an electron donor (e.g., formate) was necessary to reduce the recombination rate and achieve efficient nitrate removal. Nano-sized photocatalysts with high surface areas mitigated the negative effects of competing aqueous anions. The key water quality parameter impacting by-product selectivity was pH. For pH < 4, the by-product selectivity was mostly N-gas with some NH4+, but this shifted to NO2- above pH = 4, which suggests the need for proton localization to move beyond NO2-. Co-catalysts that form a Schottky barrier, allowing for localization of electrons, were best for nitrate reduction. Silver was optimal in heterogeneous systems because of its ability to improve nitrate reduction activity and N-gas by-product selectivity, and graphene was optimal in two-electrode systems because of its ability to shuttle electrons to the working electrode. "Environmentally responsible use of nanomaterials" is to ensure that detection methods are in place for the nanomaterials tested. While methods exist for the metals and metal oxides examined, there are currently none for carbon nanotubes (CNTs) and graphene. Acknowledging that risk assessment encompasses dose-response and exposure, new analytical methods were developed for extracting and detecting CNTs and graphene in complex organic environmental (e.g., urban air) and biological matrices (e.g. rat lungs).
ContributorsDoudrick, Kyle (Author) / Westerhoff, Paul (Thesis advisor) / Halden, Rolf (Committee member) / Hristovski, Kiril (Committee member) / Arizona State University (Publisher)
Created2013
Description
Chloroform (CHCl3) is an important atmospheric pollutant by its direct health effects as well as by its contribution to photochemical smog formation. Chloroform outgassing from swimming pools is not typically considered a source of atmospheric CHCl3 because swimming pools are scarce compared to other sources. However, large urban areas in hot climates such as Phoenix, AZ contain a substantial amount of swimming pools, potentially resulting in significant atmospheric fluxes. In this study, CHCl3 formation potential (FP) from disinfection of swimming pools in Phoenix was investigated through laboratory experiments and annual CHCl3 emission fluxes from swimming pools were estimated based on the experimental data.
Swimming pool water (collected in June 2014 in Phoenix) and model contaminants (Pharmaceuticals and Personal Care Products (PPCPs), Endocrine Disrupting Compounds (EDCs), artificial sweeteners, and artificial human waste products) were chlorinated in controlled laboratory experiments. The CHCl3 production during chlorination was determined using Gas Chromatography-Mass Spectrometry (GC-MS) following solid-phase microextraction (SPME). Upon chlorination, all swimming pool water samples and contaminants produced measureable amounts of chloroform. Chlorination of swimming pool water produced 0.005-0.134 mol CHCl3/mol C and 0.004-0.062 mol CHCl3/mol Cl2 consumed. Chlorination of model contaminants produced 0.004-0.323 mol CHCl3/mol C and 0.001-0.247 mol CHCl3/mol Cl2 consumed. These numbers are comparable and indicate that the model contaminants react similarly to swimming pool water during chlorination. The CHCl3 flux from swimming pools in Phoenix was estimated at approximately 3.9-4.3 Gg/yr and was found to be largely dependent on water temperature and wind speed while air temperature had little effect. This preliminary estimate is orders of magnitude larger than previous estimates of anthropogenic emissions in Phoenix suggesting that swimming pools might be a significant source of atmospheric CHCl3 locally.
Swimming pool water (collected in June 2014 in Phoenix) and model contaminants (Pharmaceuticals and Personal Care Products (PPCPs), Endocrine Disrupting Compounds (EDCs), artificial sweeteners, and artificial human waste products) were chlorinated in controlled laboratory experiments. The CHCl3 production during chlorination was determined using Gas Chromatography-Mass Spectrometry (GC-MS) following solid-phase microextraction (SPME). Upon chlorination, all swimming pool water samples and contaminants produced measureable amounts of chloroform. Chlorination of swimming pool water produced 0.005-0.134 mol CHCl3/mol C and 0.004-0.062 mol CHCl3/mol Cl2 consumed. Chlorination of model contaminants produced 0.004-0.323 mol CHCl3/mol C and 0.001-0.247 mol CHCl3/mol Cl2 consumed. These numbers are comparable and indicate that the model contaminants react similarly to swimming pool water during chlorination. The CHCl3 flux from swimming pools in Phoenix was estimated at approximately 3.9-4.3 Gg/yr and was found to be largely dependent on water temperature and wind speed while air temperature had little effect. This preliminary estimate is orders of magnitude larger than previous estimates of anthropogenic emissions in Phoenix suggesting that swimming pools might be a significant source of atmospheric CHCl3 locally.
ContributorsRose, Christy J (Author) / Herckes, Pierre (Thesis advisor) / Fraser, Matthew (Committee member) / Hayes, Mark (Committee member) / Westerhoff, Paul (Committee member) / Arizona State University (Publisher)
Created2014
Description
Population growth and fresh water depletion challenge drinking water utilities. Surface water quality is impacted significantly by climate variability, human activities, and extreme events like natural disasters. Dissolved organic carbon (DOC) is an important water quality index and the precursor of disinfection by-products (DBPs) that varies with both hydrologic and anthropogenic factors. Granular activated carbon (GAC) is a best available technology for utilities to meet Stage 2 D/DBP rule compliance and to remove contaminants of emerging concern (CECs) (e.g., pharmaceutical, personal care products (PCPs), etc.). Utilities can operate GAC with more efficient and flexible strategies with the understanding of organic occurrence in source water and a model capable predicting DOC occurrence. In this dissertation, it was found that DOC loading significantly correlated with spring runoff and was intensified by dry-duration antecedent to first flush. Dynamic modeling based on reservoir management (e.g., pump-back operation) was established to simulate the DOC transport in the reservoir system. Additionally, summer water recreational activities were found to raise the level of PCPs, especially skin-applied products, in raw waters. GAC was examined in this dissertation for both carbonaceous and emerging nitrogenous DBP (N-DBP) precursors (i.e., dissolved organic nitrogen (DON)) removal. Based on the experimental findings, GAC preferentially removes UV254-absorbing material, and DOC is preferentially removed over DON which may be composed primarily of hydrophilic organic and results in the low affinity for adsorption by GAC. The presence of organic nitrogen can elevate the toxicity of DBPs by forming N-DBPs, and this could be a major drawback for facilities considering installation of a GAC adsorber owing to the poor removal efficiency of DON by GAC. A modeling approach was established for predicting DOC and DON breakthrough during GAC operation. However, installation of GAC adsorber is a burden for utilities with respect to operational and maintenance cost. It is common for utilities to regenerate saturated GAC in order to save the cost of purchasing fresh GAC. The traditional thermal regeneration technology for saturated GAC is an energy intensive process requiring high temperature of incineration. Additionally, small water treatment sites usually ship saturated GAC to specialized facilities for regeneration increasing the already significant carbon footprint of thermal regeneration. An innovative GAC regeneration technique was investigated in this dissertation for the feasibility as on-site water treatment process. Virgin GAC was first saturated by organic contaminant then regenerated in-situ by iron oxide nanocatalysts mixed with hydrogen peroxide. At least 70 % of adsorption capacity of GAC can be regenerated repeatedly for experiments using modeling compound (phenol) or natural organic matter (Suwannee River humic acid). The regeneration efficiency increases with increasing adsorbate concentration. Used-iron nanocatalysts can be recovered repeatedly without significant loss of catalytic ability. This in-situ regeneration technique provides cost and energy efficient solution for water utilities considering GAC installation. Overall, patterns were found for DOC and CEC variations in drinking water sources. Increasing concentrations of bulk (DOC and DON) and/or trace organics challenge GAC operation in utilities that have limited numbers of bed-volume treated before regeneration is required. In-situ regeneration using iron nanocatalysts and hydrogen peroxide provides utilities an alternative energy-efficient operation mode when considering installation of GAC adsorber.
ContributorsChiu, Chao-An (Author) / Westerhoff, Paul (Thesis advisor) / Rittmann, Bruce (Committee member) / Hristovski, Kiril (Committee member) / Arizona State University (Publisher)
Created2012
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
With the application of reverse osmosis (RO) membranes in the wastewater treatment and seawater desalination, the limitation of flux and fouling problems of RO have gained more attention from researchers. Because of the tunable structure and physicochemical properties of nanomaterials, it is a suitable material that can be used to incorporate with RO to change the membrane performances. Silver is biocidal, which has been used in a variety of consumer products. Recent studies showed that fabricating silver nanoparticles (AgNPs) on membrane surfaces can mitigate the biofouling problem on the membrane. Studies have shown that Ag released from the membrane in the form of either Ag ions or AgNP will accelerate the antimicrobial activity of the membrane. However, the silver release from the membrane will lower the silver loading on the membrane, which will eventually shorten the antimicrobial activity lifetime of the membrane. Therefore, the silver leaching amount is a crucial parameter that needs to be determined for every type of Ag composite membrane.
This study is attempting to compare four different silver leaching test methods, to study the silver leaching potential of the silver impregnated membranes, conducting the advantages and disadvantages of the leaching methods. An In-situ reduction Ag loaded RO membrane was examined in this study. A custom waterjet test was established to create a high-velocity water flow to test the silver leaching from the nanocomposite membrane in a relative extreme environment. The batch leaching test was examined as the most common leaching test method for the silver composite membrane. The cross-flow filtration and dead-end test were also examined to compare the silver leaching amounts.
The silver coated membrane used in this experiment has an initial silver loading of 2.0± 0.51 ug/cm2. The mass balance was conducted for all of the leaching tests. For the batch test, water jet test, and dead-end filtration, the mass balances are all within 100±25%, which is acceptable in this experiment because of the variance of the initial silver loading on the membranes. A bad silver mass balance was observed at cross-flow filtration. Both of AgNP and Ag ions leached in the solution was examined in this experiment. The concentration of total silver leaching into solutions from the four leaching tests are all below the Secondary Drinking Water Standard for silver which is 100 ppb. The cross-flow test is the most aggressive leaching method, which has more than 80% of silver leached from the membrane after 50 hours of the test. The water jet (54 ± 6.9% of silver remaining) can cause higher silver leaching than batch test (85 ± 1.2% of silver remaining) in one-hour, and it can also cause both AgNP and Ag ions leaching from the membrane, which is closer to the leaching condition in the cross-flow test.
This study is attempting to compare four different silver leaching test methods, to study the silver leaching potential of the silver impregnated membranes, conducting the advantages and disadvantages of the leaching methods. An In-situ reduction Ag loaded RO membrane was examined in this study. A custom waterjet test was established to create a high-velocity water flow to test the silver leaching from the nanocomposite membrane in a relative extreme environment. The batch leaching test was examined as the most common leaching test method for the silver composite membrane. The cross-flow filtration and dead-end test were also examined to compare the silver leaching amounts.
The silver coated membrane used in this experiment has an initial silver loading of 2.0± 0.51 ug/cm2. The mass balance was conducted for all of the leaching tests. For the batch test, water jet test, and dead-end filtration, the mass balances are all within 100±25%, which is acceptable in this experiment because of the variance of the initial silver loading on the membranes. A bad silver mass balance was observed at cross-flow filtration. Both of AgNP and Ag ions leached in the solution was examined in this experiment. The concentration of total silver leaching into solutions from the four leaching tests are all below the Secondary Drinking Water Standard for silver which is 100 ppb. The cross-flow test is the most aggressive leaching method, which has more than 80% of silver leached from the membrane after 50 hours of the test. The water jet (54 ± 6.9% of silver remaining) can cause higher silver leaching than batch test (85 ± 1.2% of silver remaining) in one-hour, and it can also cause both AgNP and Ag ions leaching from the membrane, which is closer to the leaching condition in the cross-flow test.
ContributorsHan, Bingru (Author) / Westerhoff, Paul (Thesis advisor) / Perreault, Francois (Committee member) / Sinha, Shahnawaz (Committee member) / Arizona State University (Publisher)
Created2017
Description
The volume of end-of-life photovoltaic (PV) modules is increasing as the global PV market increases, and the global PV waste streams are expected to reach 250,000 metric tons by the end of 2020. If the recycling processes are not in place, there would be 60 million tons of end-of-life PV modules lying in the landfills by 2050, that may not become a not-so-sustainable way of sourcing energy since all PV modules could contain certain amount of toxic substances. Currently in the United States, PV modules are categorized as general waste and can be disposed in landfills. However, potential leaching of toxic chemicals and materials, if any, from broken end-of-life modules may pose health or environmental risks. There is no standard procedure to remove samples from PV modules for chemical toxicity testing in the Toxicity Characteristic Leaching Procedure (TCLP) laboratories as per EPA 1311 standard. The main objective of this thesis is to develop an unbiased sampling approach for the TCLP testing of PV modules. The TCLP testing was concentrated only for the laminate part of the modules, as they are already existing recycling technologies for the frame and junction box components of PV modules. Four different sample removal methods have been applied to the laminates of five different module manufacturers: coring approach, cell-cut approach, strip-cut approach, and hybrid approach. These removed samples were sent to two different TCLP laboratories, and TCLP results were tested for repeatability within a lab and reproducibility between the labs. The pros and cons of each sample removal method have been explored and the influence of sample removal methods on the variability of TCLP results has been discussed. To reduce the variability of TCLP results to an acceptable level, additional improvements in the coring approach, the best of the four tested options, are still needed.
ContributorsLeslie, Joswin (Author) / Tamizhmani, Govindasamy (Thesis advisor) / Srinivasan, Devarajan (Committee member) / Kuitche, Joseph (Committee member) / Arizona State University (Publisher)
Created2018
Description
Due to the use of fertilizers, concentrations of harmful nitrate have increased in groundwater and surface waters globally in the last century. Water treatment plants primarily use separation techniques for nitrate treatment, but these technologies create a high nitrate concentration brine that is costly to dispose of. This dissertation focuses on catalytic hydrogenation, an emerging technology capable of reducing nitrate to nitrogen gas using hydrogen gas (H2). This technology reduces nitrate at rates >95% and is an improvement over technologies used at water treatment plants, because the nitrate is chemically transformed with harmless byproducts and no nitrate brine. The goal of this dissertation is to upgrade the maturity of catalytic nitrate hydrogenation systems by overcoming several barriers hindering the scale-up of this technology. Objective 1 is to compare different methods of attaching the bimetallic catalyst to a hollow-fiber membrane surface to find a method that results in 1) minimized catalyst loss, and 2) repeatable nitrate removal over several cycles. Results showed that the In-Situ MCfR-H2 deposition was successful in reducing nitrate at a rate of 1.1 min-1gPd-1 and lost less than 0.05% of attached Pd and In cumulatively over three nitrate treatment cycles. Objective 2 is to synthesize catalyst-films with varied In3+ precursor decorated over a Pd0 surface to show the technology can 1) reliably synthesize In-Pd catalyst-films with varied bimetallic ratios, and 2) optimize nitrate removal activity by varying In-Pd ratio. Results showed that nitrate removal activity was optimized with a rate constant of 0.190 mg*min-1L-1 using a catalyst-film with a 0.045 In-Pd ratio. Objective 3 is to perform nitrate reduction in a continuous flow reactor for two months to determine if nitrate removal activity can be sustained over extended operation and identify methods to overcome catalyst deactivation. Results showed that a combination of increased hydraulic residence time and reduced pH was successful in increasing the nitrate removal and decreasing harmful nitrite byproduct selectivity to 0%. These objectives increased the technology readiness of this technology by enabling the reuse of the catalyst, maximizing nitrate reduction activity, and achieving long-term nitrate removal.
ContributorsLevi, Juliana (Author) / Westerhoff, Paul (Thesis advisor) / Rittmann, Bruce (Thesis advisor) / Garcia-Segura, Sergi (Committee member) / Wong, Michael (Committee member) / Lind Thomas, Mary Laura (Committee member) / Emady, Heather (Committee member) / Arizona State University (Publisher)
Created2023