Human senses for taste, odor, and visual assessment allow consumers to be selective when it comes to choosing their drinking water. In addition to wanting aesthetically pleasing water to drink, consumers want to know if their water is safe and may have misconceptions on what possible health risk contaminants could be lurking in their water supply. This thesis aimed to measure reaction of zerovalent nanoiron (nZVI) in water and human saliva, evaluate consumer's perceptions of taste, odor, and risk in their drinking water, and investigate the effectiveness of community water systems in communicating water quality information to their consumers. Since nZVI, including commercially available Nanofer 25S, is widely being used in water treatment processes and has future potential for use in fortifying foods, the exposure to these engineered nanoparticles will increase for humans and aquatic organisms. Thus, the first part of the thesis was to develop a quantitative analytical technique to measure the iron levels at environmentally relevant concentrations. Researchers developed a colorimetric assay using 1, 10-phenanthroline as an assay to determine the amount of ferrous ions produced from different iron materials, including ferrous(II)sulfate, nZVI, and goethite. Resulting ferrous ion measurements indicate that the maximum production of ferrous ions varied among the iron materials. Nanofer25S did not undergo 100% conversion to ferrous ions, as expected, goethite had no production of ferrous ions, and ferrous(II)sulfate was 100% ferrous ions. The total iron, as measured by atomic absorption for all iron materials were equal. The reactivity of these iron materials were also assessed in different water qualities ranging in salt concentrations. The capacity to produce ferrous ion did not change when added to nanopure water, tap water, and inorganic solution that is equivalent to the high ionic strength of saliva. Toxicology data for nZVI exposure to humans and aquatic organisms are limited. For that reason, authors of this manuscript measured salivary lipid oxidation (SLO) potential for the different iron materials in human saliva. They also developed an artificial saliva recipe to ensure repeatability and comparable results among laboratories due to human saliva's variability day by day. This simulated human saliva contained salts, proteins, and lipids. Using thiobarbituric acid reactive substances (TBARs), both Nanofer25S and ferrous(II)sulfate induced in-vitro SLO with human saliva. Goethite was unreactive. SLO results from this study have implications for flavor effects of nZVI in drinking water. The second chapter of this thesis is assessing the clarity of message communication of Consumer Confidence Reports (CCRs). In 1998, the United States Environmental Protection Agency (USEPA) mandated that community water systems (CWSs) provide annual water quality reports to their consumers. These CCRs summarize information regarding water sources, any detected contaminants, compliance with federal regulations, and educational information. Thirty CCRs across all ten USEPA regions were analyzed for clarity using the Centers for Disease Control and Prevention's (CDC) Clear Communication Index (CCI) tool. The analysis of these CCRs was a national representation of CWSs and revealed that currently distributed CCRs performed poorly on the CDC's CCI—all failing to meet the 90% passing mark. The overall average score for all CCRs was 50.3 ± 13.5%. The clarity scores were based on seven key areas: 1) Main message and call to action; 2) Language; 3) Information design; 4) State of the science; 5) Behavioral recommendations; 6) Numbers; and 7) Risk. Improvements in all seven areas—with the lowest average scores at 3.3 ± 18.1%, 21.7 ± 26.6%, and 37.7 ± 27.1%, respectively, for state of science, language, and main message and call to action—of the CCI will greatly improve the quality and educational capabilities of CCRs. The failing scores highlight the challenges facing CWSs in communicating water quality information. This assessment can serve as a tool for water utilities to effectively prepare and distribute information to their consumers in the future. CWSs must promote a two-way dialogue with their consumers. They should address consumer's concerns and wants in the CCRs, and they should also effectively communicate risks to the consumers so that they are not under the misconception that their water is unsafe to drink. CWSs should use the CCRs as a way to educate the public and promote drinking tap water. The last chapter of this thesis addresses the concerns that consumers may have about their drinking water and methods that could be implemented to quickly and efficiently respond to consumer complaints and contaminants with sensory properties. Just like CWSs, consumers are concerned about their water; they are the sentinels to water quality monitoring because they are uniquely positioned at the tap. Consumers are able to detect the slightest taste, odor, and appearance in their drinking water because it is well—instinctive! Thus, consumer feedback and complaint data provided to a utility should be taken seriously and stored for future comparisons. Any consumer complaint represents a fruitful data stream that should be harnessed routinely to gain knowledge about aesthetic water quality in the distribution system. Four utilities provided consumer complaints on water quality data that were categorized and visualized using radar and run-time plots. As a result, major taste, odor, and appearance patterns emerged that clarified the issue and could provide guidance to the utilities on the nature and extent of the problem. Consumer complaint data is valuable for water quality issue identification, but CWSs should understand that even though humans readily identify visual issues with water, such as color, cloudiness, or rust, describing specific tastes and particularly odors in drinking water is acknowledged to be a much more difficult task for humans to achieve without training. This was demonstrated with two utility groups, laboratory personnel and plant operators, and a group of consumers identifying the odor of orange, 2-MIB, and DMTS. All of the groups were able to identify the familiar orange odor. However, the two utility groups were much more able to identify the musty odor of 2-MIB; this may be due to the fact that the utility groups are more familiar with raw and finished water. DMTS, a garlic-onion odor associated with sulfur compounds in drinking water, was the least familiar to all three groups. The lab personnel group was the better describers of the odor, but the results within this group still varied significantly. These results suggest that utility personnel should be mindful of consumers who complain that their water is different, but cannot describe the problem. To reduce the inability to describe an odor or taste issue, a TandO program at a utility can be beneficial. The safety and aesthetic characteristics of drinking water is most important to consumers. They both complement each other; if consumers think their water tastes funny, they would probably assume that is unsafe to drink. Since nZVI is increasingly being introduced into the drinking water supply, researchers must be able to understand how it reacts in humans and the environment. Additionally, CCRs would be an effective method for CWSs to communicate water quality information and address any concerns consumers may have about their water. CWSs can use implement the radar and run-time plots to identify issues in the drinking water systems. Also, TandO programs will allow CWSs and their consumers to better describe and identify the issues in their drinking water as it arises so that it can be easily addressed and alleviated. Thus, promoting communication between water utilities and their consumers will improve the relationship and instill confidence in consumers about their drinking water. / Master of Science

Three odor control chemicals and formaldehyde were tested for detrimental affects on activated sludge using bench-scale bioreactors. Slug fed and continuous flow bioreactors were monitored for changes in suspended solids, specific oxygen uptake rate, sludge settling and compaction, and effluent COD. The biodegradability of dyes and the generation of foam was also measured. Formaldehyde and the formaldehyde-based odor control chemical "Aqua-Kem" damaged the ability of activated sludge to treat wastewater. They resulted in deceased suspended solids concentrations and increased effluent COD. Formaldehyde hinders the utilization of normal wastewater substrate by activated sludge. The dye in "Aqua-Kem" is not biodegradable, and surfactants in the chemical generate foam. / Master of Science

Chlorine (Cl₂(sq»' chlorine dioxide (ClO₂ ) and potassium permanganate (KMnO₄) were evaluated as oxidants for the removal of grassy and cucumber odors associated with the pure compounds, cis-3-hexenol and trans-2, cis-6-nonadienal, respectively, and for the removal of fishy odors associated with a culture of an alga, Synura petersenii. The effects of the oxidants on the pure compounds were assessed both by Flavor Profile Analysis (FPA) and gas chromatography/mass spectrometry (GC/MS). The effects of the oxidants on the algae culture were evaluated by FPA only. In addition, an unoxidized sample of Synura petersenii was analyzed by gas chromatography coupled with mass spectrometry (GC/MS) for possible identification of fishy-smelling compounds. Chlorine (1-6 mg/L) and KMn04 (0.25-4 mg/L) markedly reduced grassy and cucumber odors associated with the two compounds. Gas chromatography/mass spectrometry confirmed that these compounds were reduced to below method detection limits. Levels of Cl₂(&q) required (up to 6 mg/L) to reduce the grassy odors associated with cis-3-hexenol were higher than those of KMnO₄ â ¢ The high Cl₂(&q) doses may have contributed to the formation of chemical odors observed by panelists. Two isomers of chlorohexenol were confidently identified as byproducts of cis-3-hexenol chlorination and may have contributed to the chemical odors that developed after CI2(aq) treatment. Chlorine and KMnO₄ (both at 10 mg/L) either reduced or destroyed the fishy odor associated with the culture of Synura petersenii; however, oxidation caused either the development or unmasking of fruity, cucumber, melon and grassy odors. Chlorine dioxide (3 mg/L) did not reduce the grassy and cucumber odors associated with cis-3-hexenol and trans-2, cis-6-nonadienal , respectively. Gas chromatography and mass spectrometry confirmed that concentrations of these compounds were not reduced to below method detection limits. Furthermore, at a concentration of 10 mg/L, Cl₂ did not effectively reduce either the fishy or other objectionable odors associated with Synura petersenii culture. Hexanal, with an odor described as "green" or "like lettuce heart," and trans-2, cis-6-nonadienal (cucumber odor) were confirmed as algal products in a two-week-old culture of Synura petersenii. In addition, decatrienal was confidently identified as a product of Synura and may have contributed to the fishy odor associated with this alga. / Master of Science

The effects of lime and sodium hydroxide on gas production from stored sewage sludge were examined. The impact of calcium on gas production was also investigated. The rate and volume of gas production and change in pH over time were monitored in all the reactors in an effort to study the relationship between chemical dose, pH, and gas production. The duration of inhibition of gas production increased with the lime dose. Gas production was initiated only after the pH in the reactors decreased to near 8.0. A decrease in pH was observed in all the lime dosed reactors with an initial pH less than 12.0. An initial pH greater than 12.0 was required to completely arrest organic acid and gas production. For the sludge used in this study, a quick lime dose of 0.36 Ib/lb of dry solids, which elevated the pH to higher than 12.0, was required for complete inhibition of gas production. Gas production and pH patterns observed in sodium hydroxide dosed reactors were similar to those in lime dosed reactors. A decrease in pH by nearly 2 pH units was observed in these reactors after calcium chloride addition. This was thought to be primarily due to the precipitation of calcium carbonate. Gas production after elutriation was observed in all the reactors with an initial pH less than 11.5. The volume of gas produced after elutriation decreased with increase in initial pH. An NaOH (19N) dose of 0.29 Ib/Ib of dry solids was required for permanent prevention of gas production. Calcium alone was not capable of arresting gas production but it reduced the total gas production in the reactors with a pH less than 7.5. At pH values greater than 7.5, calcium had little effect on gas production. / Master of Science

Although utilities attempt to avoid offensive smelling compounds in consumer's drinking water, their efforts are often hampered by a lack of data or knowledge of the physical, chemical, and sensory properties of odorants. Many factors affect the ability of a consumer to detect odors, including: concentration, presence of chlorine/other odorants, temperature, and the individual's sensitivity. This research developed a simplified static-headspace technique to determine Henry's Law constants at multiple temperatures and then use these data to calculate the enthalpy of solution so that new Henry's Law constants can be calculated at any temperature using the van't Hoff Equation. The method was applied to three taste-and-odor compounds of moderate water solubility (about 100 mg/L). 2-Methylisoborneol (2-MIB) is a methylated monoterpene alcohol that is produced by actinomycetes and blue-green algae and has a musty odor that is detectable at 4-10 ng/L water. Geosmin, also produced by actinomycetes and blue-green algae, has a detectable earthy odor at 5-10 ng/L. trans-2, cis-6-Nonadienal is enzymatically synthesized from poly-unsaturated fatty acids by diatoms like Synura and has cucumber and fishy odors detectable at 10-40 ng/L levels. The new static headspace method uses standard glassware used in odor-analyses. 500 mL wide-mouth Erlenmeyer flasks were modified with septum sampling ports to measure vapor phase concentrations by SPME/GC-MS. Unitless Henry's Law constants were determined at multiple temperatures using the vapor and aqueous phase concentrations. From the Henry's Law constants, the enthalpies of reactions were calculated. For these compounds, the values for Henry's Law constants ranged from 0.002 to 0.02 for four temperatures between 20 to 45 °C with geosmin and 2-MIB having similar and higher values than for nonadienal. The constants increased with increasing temperature. The enthalpies of vaporization from the aqueous phase were determined to be in the range of 50-80 kJoule/mole. The experiments were repeated with fulvic acid added to the aqueous media at different concentrations. The Henry's Law constants were decreased with the presence of fulvic acid; however no correlation between the concentration of fulvic acid and the decrease was observed. The decrease in constants for 2-MIB and geosmin were very small compared to nonadienal. Finally the measured Henry's Law constants were used to predict gas phase concentrations of odorants for known aqueous concentrations of geosmin, 2-MIB, and nonadienal. The results were correlated to the human sensory data obtained from flavor profile analysis. The data demonstrated that as the gas phase concentration increased, the perceived odor intensity also increased, but only up to a certain point. The vapor phase concentration increased linearly as the aqueous phase concentration increased, but the FPA intensity increased at a lower rate and leveled-off. The increase in the FPA rating at 25ï °C was greater than at 45 °C although the vapor phase concentration was greater at 45 °C. For samples containing 400 and 600 ng/L geosmin, 400 and 600 ng/L, 2-MIB, 100 and 200 ng/L nonadienal, the increase in gas phase concentration did not increase the FPA ratings of the panelists. It was concluded that, utilities will be challenged to assess and treat high concentrations of geosmin, 2-MIB, and nonadienal. Sensory analysis will not be predictive of aqueous or vapor concentration at high levels and may be misleading if used to determine a treatment strategy. Chemical analyses, especially solid phase microextraction technique is very effective in measuring these compounds even at low ng/L levels. The temperature-related Henry's Law constants can be used to assess remediation systems, human exposure and sensory perception by predicting gas phase concentration in a variety of situations, such as showering and washing dishes. / Master of Science

This study is aimed to provide comprehensive evaluation and mechanistic understanding of the impact of process intensification techniques applied in main and side stream wastewater treatment on biosolids management in terms of anaerobic digestion enhancement, dewaterability improvement, odor mitigation, as well as phosphorus and nitrogen removal. The first part of this study was conducted to understand the effect of anaerobic digester solids retention time (SRT) on odor emission from biosolids. A kinetic model and inhibitory studies showed the emission of methanethiol (MT), a representative odor compound, was primarily determined by the dynamic concurrence of MT production from amino acid and utilization by methanogens in the course of anaerobic digestion. MT emission pattern follows a bell-shape curve with SRT in anaerobic digesters. However, for digested and dewatered biosolids, SRT ranging from 15 to 50 days in anaerobic digesters demonstrated insignificant effect on the odor emission from biosolids. In contrast, the peak odor emission was found to exponentially increase with both shear intensity and polymer dose applied during dewatering. The second part of this study investigated the impact of process intensification practices on sludge dewatering performance. The integration of high-rate activated sludge process and anaerobic digestion elevated the sludge orthophosphate level, leading to struvite scaling and dewaterability deterioration. Superior orthophosphate removal, significant improvement of sludge dewaterability, and favorable economics were achieved through sludge conditioning by cerium chloride. Continuous flow aerobic granulation technology offered significant process intensification of mainstream treatment trains. However, its impact on biosolids management was not studied. This study showed that there was little dewaterability difference between aerobic granular sludge and activated sludge when polymer was not added. However, about 75% polymer saving and improved dewatering performance were observed with polymer addition. When subjected to high shear, a greater dewaterability deterioration was observed for granular sludge than activated sludge. The last part of this study is focused on the impact of anaerobic digestion process intensification through thermal treatment including pre-pasteurization, thermophilic anaerobic digestion, temperature phased anaerobic digestion, and thermal hydrolysis pretreatment. Improved methane production, pathogen reduction, dewatering performance, and odor mitigation were observed with the involvement of these high-temperature processes. However, special cautions and measure should be taken during the start-up of these high rate processes as they are more liable to digester souring. In addition, the in-depth understanding of the mechanism of recalcitrant dissolved organic nitrogen formation during sludge thermal pretreatment was provided. / Doctor of Philosophy / This study is aimed to provide comprehensive evaluation and mechanistic understanding of the impact of process intensification techniques applied in main and side stream wastewater treatment on biosolids management in terms of anaerobic digestion enhancement, dewaterability improvement, odor mitigation, as well as phosphorus and nitrogen removal. The first part of this study was conducted to understand the effect of anaerobic digester solids retention time (SRT) on odor emission from biosolids. A kinetic model and inhibitory studies showed the emission of methanethiol (MT), a representative odor compound, was primarily determined by the dynamic concurrence of MT production from amino acid and utilization by methanogens in the course of anaerobic digestion. MT emission pattern follows a bell-shape curve with SRT in anaerobic digesters. However, for digested and dewatered biosolids, SRT ranging from 15 to 50 days in anaerobic digesters demonstrated insignificant effect on the odor emission from biosolids. In contrast, the peak odor emission was found to exponentially increase with both shear intensity and polymer dose applied during dewatering. The second part of this study investigated the impact of process intensification practices on sludge dewatering performance. The integration of high-rate activated sludge process and anaerobic digestion elevated the sludge orthophosphate level, leading to struvite scaling and dewaterability deterioration. Superior orthophosphate removal, significant improvement of sludge dewaterability, and favorable economics were achieved through sludge conditioning by cerium chloride. Continuous flow aerobic granulation technology offered significant process intensification of mainstream treatment trains. However, its impact on biosolids management was not studied. This study showed that there was little dewaterability difference between aerobic granular sludge and activated sludge when polymer was not added. However, about 75% polymer saving and improved dewatering performance were observed with polymer addition. When subjected to high shear, a greater dewaterability deterioration was observed for granular sludge than activated sludge. The last part of this study is focused on the impact of anaerobic digestion process intensification through thermal treatment including pre-pasteurization, thermophilic anaerobic digestion, temperature phased anaerobic digestion, and thermal hydrolysis pretreatment. Improved methane production, pathogen reduction, dewatering performance, and odor mitigation were observed with the involvement of these high-temperature processes. However, special cautions and measure should be taken during the start-up of these high rate processes as they are more liable to digester souring. In addition, the in-depth understanding of the mechanism of recalcitrant dissolved organic nitrogen formation during sludge thermal pretreatment was provided.

As the bottled water trend continues to rise across the nation, drinking water utilities have become more concerned with ensuring consumer satisfaction of their product. Although public water supplies are safeguarded by regulations, aesthetically unappealing taste-and-odor problems have led consumers to search for alternative water sources, such as bottled water or tap water processed by point-of-use filters. Consequently, taste-and-odor monitoring has become important to the drinking water industry. Because many utilities use chlorine to disinfect the water, chlorine odor often masks other more subtle odors that may eventually cause consumer complaints. As treated water travels from the water treatment plant to the consumer, chlorine residual diminishes and may reveal a water's naturally less-pleasing odors. Consequently, odor monitoring at the water treatment plant, where chlorine concentrations are at a peak, may not identify potential displeasing smells. Proper evaluation of these odor-causing substances requires that the chlorine odor first be eliminated before evaluating any remaining odors. Dechlorinating agents can remove chlorine, but some will produce other unwanted odors or even remove certain odorous compounds. This research describes the efficiency of several of these agents (ascorbic acid, hydrogen peroxide, oxalic acid, sodium nitrite, and sodium thiosulfate) in dechlorinating chlorinated solutions of the earthy-smelling compound geosmin and musty-smelling MIB. Interfering odors in reusable containers pose another problem in drinking water odor analysis. The most common odor-analysis methods (TON and FPA) involve the use of glass flasks, which often either develop chalky odors or have persistent lingering odors from previous evaluations. Furthermore the glass flasks break easily and are difficult to clean. This research also evaluates the suitability of four types of disposable plastic containers for odor analyses. / Master of Science

Fish and crab processing wastes were ground and ensiled with corn stover or peanut hulls alone and with 5% dry molasses or 1% formic acid in 3.8 liter cardboard containers double lined with polyethylene. The wastes and roughages were ensiled in proportion to give dry matter levels of 40, 50 and 60%. The seafood wastes were also ensiled with wilted Johnsongrass with and without molasses. After ensiling, average pH for mixtures with fish waste was 6.5, compared to 8.0 for mixtures with crab waste. Addition of dry molasses resulted in a decrease (P <.01) of pH to 5.6 for the ensiled fish mixture but had no effect on the crab waste mixtures. Lactic acid was higher (P< .01) for ensiled mixtures containing fish waste than for those containing crab waste. Substantial levels of acetic acid were present in the silages. Butyric acid levels were higher in silages containing crab waste and decreased linearly (P< .01) with increased dry matter levels. Desirable ensiling was observed for the mixture of fish waste and Johnsongrass. Coliforms and fecal coliforms were decreased or elIminated by ensiling. In a large silo study, mixtures of finfish and crab processing wastes were mixed with wheat straw and ensiled in 210 liter metal drums, double lined with polyethylene bags. Proportions of the fish and straw were 70:30 and 51:49, wet basis, while that of the crab was 60:40 and 40:60. Acetic acid was added to the crab waste mixtures to lower the initial pH to 4.5. After ensiling all mixtures containing fish and straw showed a decrease in pH. Addition of acetic acid to mixtures containing crab waste inhibited fermentation, but resulted in a very stable product. In a sheep digestion trial, dry matter digestibility was higher (P <.01) for the 70:30 diet than for the 51:49 fish diet. There was no difference in dry matter digestibility between the crab silages. Crude protein digestibility was higher (P <.01) for diets containing ensiled fish, compared to diets containing ensiled crab. Nitrogen retention was positive for sheep receiving all diets. Nitrogen retention was higher (P <.01) for animals fed the crab silage diets, compared to those receiving diets containing fish silage. There was a trend for P absorption to be higher in animals fed crab silage. In the sheep palatability trial, intake of dry matter was higher (P < .01) for sheep consuming the crab silage diet and lowest (P <.01) for sheep fed the 70:30 fish silage diet. / Ph. D.

In February 2014, a coal ash spill on Duke Energy's Dan River Plant in Eden, NC released approximately 39,000 tons of coal ash into the Dan River. It took approximately one week to stop the spill. Starting in February 2015, drinking water utilities using the Dan River experienced a series of taste and odor (TandO) events described as "earthy" or "musty". Similar TandO events were not documented before the coal ash spill. This research attempted to understand causes of the TandO events and if the coal ash spill was connected. A variety of water quality analyses were performed on twelve sites from August 2016 to September 2017 on the Dan and Smith Rivers. The Smith River served as the control. From concentrations of coal ash indicators (particularly Ba, Sr, As, V, and Br-), there was a signature of coal ash on the Dan River that was not present on the Smith River. The signature could not be attributed to the coal ash spill, as the signature was present upstream of the spill. Chronic ecosystem toxicity due to metals was low and not significantly different between the Dan and Smith Rivers. No substantial TandO events occurred during the period of this study. All monitored odorants were detected with varying frequencies in both the Dan and Smith Rivers. No significant change in odorant concentration was found above and below the location of the coal ash spill. / MS / In February 2014, a coal ash spill from Duke Energy’s Dan River Plant in Eden, NC released approximately 39,000 tons of coal ash into the Dan River. Starting in February 2015, drinking water utilities using the Dan River experienced a series of taste and odor (T&O) events described as smelling “earthy” or “musty”. Similar T&O events were not documented before the coal ash spill. This research attempted to understand underlying causes of these T&O events and to determine if the coal ash spill was connected. Analyses, including concentrations of coal ash indicators and odorants, were performed from August 2016 to September 2017 on a monthly basis for both the Dan and Smith Rivers. The Smith River served as a control river as it was not impacted by coal burning power plants and or a coal ash spill. There was a signature of coal ash metal contamination in the Dan River but not in the Smith River. The coal ash signature could not be attributed to the 2014 Duke Energy coal ash spill in Eden, NC because it was also found upstream of the area sampled and the location of the coal ash spill. Chronic ecosystem toxicity due to metals was low on the both the Dan and Smith Rivers and was not different between the rivers. No substantial drinking water taste and odor events occurred during the study period. All monitored earth-musty odorants were detected with varying frequency at concentrations mostly below and sometimes above their individual odor threshold concentration.

Trimethylamine, (CH3)3N, (TMA), odors are often associated with limed and polymer conditioned sludges. This odor has a fishy smell and can be a nuisance to the community surrounding a wastewater treatment plant or land application site. Several factors are thought to determine the amount of TMA generated from limed biosolids. These are, the presence of cationic polymer, the polymer dose, the time between addition of polymer and lime stabilization, shear imparted on the sludge in the dewatering process and dewatered cake solids concentration. All of these were investigated in this study. The results showed that TMA could be generated from sludge that did not contain polymer but the concentrations were low compared to sludge conditioned with cationic polymer. As the polymer dose increased, the TMA increased. Shear also showed to play an important role for TMA production. In addition to higher shear increasing the polymer demand, shear in itself can increase TMA generation. However, the most important factor in generating TMA was the time between conditioning and liming. If this time was minimized, little TMA was produced, even at high polymer doses. Data also suggests that methanogens play an important role in the breakdown of TMA. / Master of Science