Public water supplies contain disease-causing microorganisms in the water or distribution ducts. In order to kill off these pathogens, a disinfectant, such as chlorine, is added to the water. Chlorine is the most widely used disinfectant in all U.S. water treatment facilities. Chlorine is known to be one of the most powerful disinfectants to restrict harmful pathogens from reaching the consumer. In the interest of obtaining a better understanding of what variables affect the levels of chlorine in the water, this thesis will analyze a particular set of water samples randomly collected from locations in Orange County, Florida. Thirty water samples will be collected and have their chlorine level, temperature, and pH recorded. A linear regression analysis will be performed on the data collected with several qualitative and quantitative variables. Water storage time, temperature, time of day, location, pH, and dissolved oxygen level will be the independent variables collected from each water sample. All data collected will be analyzed through various Statistical Analysis System (SAS®) procedures. Partial residual plots will be used to determine possible relationships between the chlorine level and the independent variables and stepwise selection to eliminate possible insignificant predictors. From there, several possible models for the data will be selected. F tests will be conducted to determine which of the models appears to be the most useful. All tests will include hypotheses, test statistics, p values, and conclusions. There will also be an analysis of the residual plot, jackknife residuals, leverage values, Cook’s D, press statistic, and normal probability plot of the residuals. Possible outliers will be investigated and the critical values for flagged observations will be stated along with what problems the flagged values indicate.

The FSMA Produce Safety Rule (PSR) requires citrus packers to more closely assess, manage, and monitor food safety risks. Although there have been no foodborne illness outbreaks and only one recall in fresh citrus, the risk of pathogens coming in on the fruit and cross contamination during washing still exists. Packhouses have dynamic washing systems and in-plant validations may be the only way to demonstrate compliance with the PSR. In-plant validations use surrogates in place of pathogens, and none have been identified or validated for citrus. The aim of this research was to identify a surrogate for use in fresh citrus packhouses. Potential surrogates were screened for free chlorine resistance, survival under commercial storage conditions, and shedding and attachment characteristics during simulated washing. E. faecium NRRL B-2354 and P. pentosaceus NRRL B-14009 were selected for further study. Resistance to chlorine was not significantly different between E. faecium and L. monocytogenes FSL J1-031 when exposed to 3 ppm free chlorine for 30, 60, 90, and 120 s at 20 and 100 ppm TSB (pE. faecium and P. pentosaceus behavior was significantly different than L. monocytogenes (p=0.05), indicating that neither is a suitable surrogate. In shedding and attachment, either the fruit (shedding) or water (attachment) was inoculated, washing was simulated, and organisms were enumerated from the water (shedding) or fruit (attachment). Both potential surrogates were statistically different than L. monocytogenes (pE. faecium can be used for L. monocytogenes shedding estimates and E. faecium and P. pentosaceus can be used for attachment estimates. Overall, this research suggests that E. faecium NRRL B-2354 can be considered as a surrogate for L. monocytogenes in whole, fresh citrus validation studies on chlorinated washes and – with appropriate adjustments – on shedding and attachment characteristics.

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This thesis addresses two hypotheses: 1) ooplasmic ion activity is regulated during water uptake by locust eggs, and, 2) activities of Ca⁺⁺ and H⁺ are maintained at levels appropriate for their use as signals for developmental processes, including activation, in insect eggs. Hypothesis 1 is based on the perturbing effect of large changes in intracellular Na and/or K activity on enzyme function in eukaryotic cells. Hypothesis 2 is based on the ionic hypothesis of activation developed from studies of eggs of marine invertebrates. Electrical potential difference across egg membranes (PD_egg), and ooplasmic activities of Na⁺, K⁺, Cl⁻, Ca⁺⁺ and H⁺ were measured with double-barrelled ion-selective microelectrodes. Locust eggs maintained a measurable potential difference across egg membranes throughout development. Input resistance (Rᵢₙ) decreased by approximately 5-fold in eggs after fertilization suggesting that the chorion is not the major barrier to ion movements into and out from the egg. Chilling and anoxia decreased the contribution of a metabolic component to PD_egg. The effects of hypercapnia on PD_egg and ooplasmic pH suggest that the metabolic component may be a H⁺-pump. Chloride diffusion contributes to PD_egg in eggs after fertilization; contributions of other ions were relatively small. Potential differences measured in internally perfused locust eggs after osmotic lysis of the serosal epithelium indicated that the chloride-dependent component of PD_egg is developed across the chorion and/or serosal cuticle. In vivo values of PD_egg are probably less negative than values measured in control saline because chloride content of ground water is low. Ooplasmic sodium and potassium activities remained at typically intracellular levels during water uptake, possibly due to release from internal stores. Chloride activities were typical of extracellular fluids and were not regulated during water uptake. Measurements of pH and pea in locust eggs are consistent with the increases in these parameters predicted by the ionic hypothesis of activation. calcium activity in the ooplasm of unfertilized locust eggs (pCa 6.4 -4.9) appeared to be at a level appropriate for the use of calcium as a signal or second messenger. Calcium activity increased 100fold within 1 day of fertilization, and 1000-fold by day 3. Calcium entry from external sources at fertilization and release from internal stores later in development may contribute to the progressive increase in ooplasmic Ca⁺⁺ activity. The ooplasm likely alkalinizes after oviposition as ambient pCo₂ declines. Available data suggest a metabolically-dependent proton pump may control ooplasmic pH in locust eggs, in contrast to the Na⁺/H⁺ exchanger implicated in alkalinization of marine invertebrate eggs. / Thesis / Master of Science (MS)

Failure to monitor the quality of drinking water can have devastating consequences. The development and implementation of sensing technology can be a crucial aspect of water quality control strategies. Chemiresistive sensors can be installed at any point of the distribution system and can provide real-time data on the levels of different water quality parameters. These sensors work by detecting changes in the conducting properties of a transducing element, induced by interactions with the analyte. Nanocarbon films have attracted interest as possible transducing materials because of their similarities to graphene, a two-dimensional material known for its exceptional electron transport properties. This thesis explores the fabrication and sensing performance of few layer graphene (FLG) and graphene-like carbon (GLC) films. The FLG sensors were used to detect copper ions in water, while the GLC sensors were used to monitor the concentration of free chlorine. The films were functionalized to improve selectivity and showed noticeable changes in their conducting properties as a result of charge transfer between them and the analyte. These changes were quantified by probing the sensors with a constant voltage and they were found to be dependent on the concentration of the analyte over a wide dynamic range. Overall, the work presented in this thesis suggests that, by tuning the selectivity of the films, nanocarbon based chemiresistive sensors can be a universal solution to water quality monitoring. / Thesis / Master of Science (MSc)