The results from this study show how different precursors affect halonitromethane (HNM) formation as well as how different free chlorine doses can affect HNM speciation. This study shows that the low pressure ultraviolet (LPUV) and free chlorine concurrent exposure can enhance HNM formation. In addition, most previous studies in the literature showed trichloronitromethane (TCNM) forming in greater quantities followed by monochloronitromethane (MCNM) and dichloronitromethane (DCNM). However, the results of this study show that, in deionized (DI) water matrices, MCNM forms in greater quantities at chlorine to nitrogen (Cl:N) ratios less than 3, while TCNM forms in greater quantities at Cl:N ratios greater than 3. Even so, the increase in TCNM formation did not increase linearly as the Cl:N ratio increased; there was a decreased rate of return when Cl:N ratios were greater than 3. The type of nitrogenous precursors can affect the amount of HNMs formed, with glycine forming a higher amount of total HNMs compared to methylamine (MA) and dimethylamine (DMA). The source of water can also affect which HNM species is formed in greater concentrations. The limited number of real water samples showed that the river waters have higher than normal total organic carbon (TOC) and dissolved organic nitrogen (DON), which are associated with greater nitrogenous precursors and higher HNM formation. Each water source can have different nitrogenous precursors; river waters may have more algal organic matter while wastewater would have higher organic matter and synthetic chemicals. In addition, source waters can have different constituents, such as varying dissolved oxygen (DO) levels and inorganic ions, which might inhibit HNM formation or affect specification.

In this thesis, low-cost free chlorine sensors for monitoring drinking water have been developed. The starting material, pencil lead, was modified using a ammonium carbamate solution. The main emphasis for this technology is the low cost, scalable and environmental friendly process. The resultant materials were highly sensitive to free chlorine. The second discovery was an advanced understanding of the unsteady state mass transfer during the sensing process, using the customly expanded Cottrell equation. This method could qualitatively indicated the absence of free chlorine, for applications where the removal of free chlorine is the goal. This method allowed better interpretation of transient data and simplified setup. The third discovery was the use of pulsed amperometric detection to detect free chlorine at a much higher sensitivity, while reducing the complexity of the setup, further reducing the cost. This method was based on the previous findings plus understanding of the reaction kinetics. The resultant sensors detected free chlorine with a detection of 0.0414 ppm, while the regulations require the free chlorine to be above 0.2 ppm. The response time was less than three seconds. The range of detection was up to around 20 ppm. The cost of materials for one sensor was less than ten dollars. The maintenance was minimal due to the lack of consumables. The operation could be as a meter or as a device in a large instrument. The target use of the sensors include small and distant communities, bottling industries, fruit and vegetable washing industries. The free chlorine sensing techniques can be readily expanded to biology, environment, and big data applications, based on the knowledge gained through the study. / Thesis / Doctor of Philosophy (PhD) / Low-cost sensors were developed to monitor free chlorine in drinking water for end users, especially in small and distant communities. Free chlorine keeps lethal microorganism pathogens from re-growing after disinfection. Re-growth is more likely to happen in these communities due to poor infrastructure and less usage-driven flow. The contributions include: • A low-cost sensing material for free chlorine based on pencil lead • Determination of operating range of the sensor • Study of sensing mechanisms • Efficiency improvement and cost reduction • Research articles, conference presentations, patent applications, and industrial collaboration based on above research The resultant sensor is easy to use, robust in practical conditions and requires low maintenance, suitable for small and distant communities. Future work is the integration with sensing systems and the application of knowledge gained in this thesis for sensing applications in other fields.

Pharmaceuticals and personal care products (PPCPs) include a wide range of chemicals such as prescription and over-the-counter drugs, fragrances, diagnostic agents, and a litany of other compounds commonly added to household products such as sunscreens, soaps, toothpastes, and deodorants. If present in natural waters, PPCPs can come into contact with disinfectants during drinking water treatment processes. PPCPs are already known to form a variety of disinfection byproducts (DBPs) when oxidized by free chlorine, including trihalomethanes (THMs) and haloacetic acids (HAAs), many of which are known carcinogens. Salts, such as iodide, are also often present in natural water systems. Iodide is known to form a much more reactive oxidant, free iodine, when it reacts with free chlorine. Free iodine can react with organic compounds in waters to form iodinated byproducts, many of which have been shown to form in higher yields and to be more toxic than their chlorinated analogues. For this reason, it is necessary to more fully understand the fate of PPCPs during drinking water processes. The overall goals of this study are to 1) elucidate reaction mechanisms and product formation potentials for PPCP oxidation by free chlorine in the presence of iodide and 2) develop a computer model that can act as a predictive tool to aid in the assessment of potential risks resulting from PPCPs in source waters. Through the course of this research, a model was developed that could fit reaction rate parameters and accurately predict solution reactivity for a range of substituted phenols as well as PPCPs including bisphenol-A and triclosan. Past studies utilizing pseudo-first-order rate constants to determine a reaction rate over-simplified the analysis of halogen substitution reactions. Free chlorine reaction rate constant values were updated from the literature since the mechanism for electrophilic substitution was found to be different than stated in currently published literature. The involvement of H₂OCl⁺ was found to be negligible. The mechanism for the electrophilic substitution of phenolic compounds by free iodide was also different from current literature findings. We found that I₂, rather than H₂OI⁺, was an extremely important species for free iodine reactions and must be considered when analyzing the reaction kinetics. Finally, we found that small amounts of iodide can significantly affect product formation pathways thereby causing preferential formation of iodinated products and a potential increase in the total product formation. In general, the reaction kinetics were highly dependent upon the pH, iodide to free chlorine ratio, and the reactivity of the phenolic compound, and our model was able to successfully address changes in each of these variables. An LFER was developed that showed a linear relationship between reaction rates and the pK_a of a phenolic compound. It is believed that the model developed can be used as a predictive tool to estimate reactivity of natural waters for a range of phenolic PPCPs simply by using the compounds pK_a. / Ph. D.

Triclosan, 5-chloro-2-(2,4 dichlorophenoxy)phenol, is an anti-microbial additive in a plethora of Pharmaceutical and Personal Care Products (PPCPs) including, toothpastes, hand creams and soaps, and acne creams. Because many triclosan containing products are topical solutions that are readily washed down the drain, significant quantities of triclosan can be introduced to wastewater treatment systems and eventually, to surface waters. Consequently, triclosan has become a contaminant of concern. The reactions between triclosan and free chlorine have been examined previously; however, no kinetic data for these reactions have been reported for conditions typical of drinking water treatment. This investigation focused specifically on the kinetics of the triclosan and free available chlorine (FAC) reactions under drinking water treatment conditions. Triclosan readily reacted with free chlorine via a second-order reaction (first order with respect to each species). No significant temperature dependency was observed from 8 to 25 °C. The reaction stoichiometry was determined to be 1:1 (triclosan oxidized per free chlorine reduced and did not vary over the pH range examined (pH 4-12). However, the reaction rate coefficients exhibited a significant pH dependency. A model that incorporates the rate coefficients for the reactions between HOCl and both neutral and anionic forms of triclosan was generated to fit the experimental data. The anionic free chlorine species hypochlorite (OCl-) was determined to play an insignificant role in the overall rate of reaction, and therefore, only the reactions involving HOCl were incorporated into the model. Additionally, a hypothesized reaction mechanism was tentatively shown to fit the collected data and its strong pH dependency. / Master of Science

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.

The kinetics, products, and reaction pathways of triclosan/free chlorine reactions were investigated for the pH range 3.5-11. Although pH dependent speciation occurs in both triclosan and free chlorine, only the reaction between HOCl and the phenolate-triclosan was found to play a significant role in the kinetics. The second order rate constant for the reaction between phenolate-triclosan and HOCl was found to be 5.40 (±1.82) Ã 103 M⁻¹s⁻¹. Three chlorinated triclosan intermediates were tentatively identified based on mass spectral analysis. Additionally, 2,4-dichlorophenol, 2,4,6-trichlorophenol, and chloroform formed under excess free chlorine conditions. The majority of the chloroform formed during the reactions does not form via 2,4-dichlorophenol and 2,4,6-trichlorophenol oxidation. Therefore, the majority of chloroform is likely formed via the oxidation of triclosan's phenolic ring. Based on the identified products, a reaction pathway was proposed for the oxidation of triclosan in the presence of free chlorine. / Master of Science

Carbamazepine (CBZ) is an antiepileptic drug widely detected in drinking water supplies and wastewater effluent. It has been previously found that CBZ is recalcitrant to biological removal processes. Therefore, active CBZ will be exposed to wastewater effluent disinfection processes, which for most treatment plants in the United States involves the addition of free chlorine. However, the chlorination mechanisms of CBZ have not been fully investigated and are currently poorly understood. Our experimental studies were conducted to examine the chlorination of CBZ under controlled conditions. The kinetics, products, and reactivity of CBZ/free chlorine reactions were investigated over the pH range of 5.5-10. Results show that free chlorine reacts with CBZ and the reactivity is pH dependent. Furthermore, the results indicate that temperature affects the reactivity of CBZ with free chlorine. The temperature experiment results were fitted with the Arrhenius equation. The calculated Ea and A values are 48.8 kJ/mol and 1.41x104 s-1, respectively. Four common intermediates were detected based on both UV and mass spectral analysis proposed structures were developed based on m/z from mass spectra. / Master of Science

<p>Organic nitrogen compounds are important in environmental systems because they are prevalent in natural waters but are also components of polymers within membrane filters that are used for water treatment. In both of these cases, these compounds can be exposed to free chlorine during disinfection, which can trigger a set of reactions that can form a host of different halogenated by-products. When such by-products form during water treatment disinfection, these by-products, known as nitrogen-based disinfection by-products (N-DBPs), can be highly toxic and affect human and ecosystem health. Alternatively, when such reactions occur during membrane filtration, the organic nitrogen compounds, which are embedded within the upper layer polymer structure of the membrane filter, can degrade when free chlorine is applied. Therefore, this research was aimed at exploring the chemistry behind how specific types of organic nitrogen compounds which are found in these applications, such as tertiary amines and amides, react with free chlorine. It particularly focused on assessing the kinetics and by-product formation of these reactions under variable water quality conditions (e.g., pH, halide concentrations, and precursor doses).</p> <p> </p> <p>More specifically, in the first phase of this work, the roles of tertiary amines in enhancing disinfection by-product (DBP) formation, such as trihalomethanes (THMs) and haloacetic acids (HAAs), during chlorination of aromatic compounds were studied. The results indicated that in synthetic solutions, chloroform (CHCl₃) and trichloroacetic acid (TCAA) were enhanced by up to 20× with tertiary amines at low dose ([tertiary amine]₀ = 0.5×[aromatic compound]₀). The enhancement effect was also dependent on the aromatic compound type, tertiary amine type and dose, and water conditions such as pH and bromide concentrations. Thus, THMs and HAAs were predicted to be enhanced when the aromatic compound reacted with R₃N-X⁺ (X=Br or Cl) and was not outcompeted by aromatic compound or tertiary amine reaction with free chlorine or bromine alone. In the second phase of this work, the reaction kinetics, by-product formation, and overall mechanisms of a polyamide-based monomer with chlorine were evaluated under varying water conditions. The current known mechanism, Orton Rearrangement, was reevaluated, and new mechanisms were proposed, where it was found that N-halogenation and ring halogenation were two independent pathways. The ability to choose either pathway was highly dependent on the water quality condition of the aqueous solution. The roles of different chlorinating/brominating agents were also investigated where certain species-specific rate constants were obtained. For the N-halogenation pathway, only chlorination and no bromination occurred in which the reactivity of the chlorinating agents likely decreased such that ClO^->HOCl. However, for the ring halogenation pathway, both chlorination and bromination occurred in which the reactivity of the chlorinating and brominating agents decreased such that Cl₂ >HOCl, and BrCl > BrOCl > Br₂ > Br₂O > HOBr, respectively. Overall, this study suggests that a number of unique reactions can occur for various types of organic nitrogen compounds which: (i) allow them to affect water quality by enhancing DBP formation, (ii) but, when integrated into a polymer matrix used for water treatment, can induce reactions that lead to permanent structural damage of the polymer. In all cases, the extent of these reactions is strongly governed by the surrounding water matrix.</p>

An ideal drinking water distribution system (DWDS) must supply safe drinking water with free chlorine residual (FCR) in the form of HOCI and OCIֿ at a required concentration level. Meanwhile the FCR is consumed in the bulk liquid phase and at the DWDS pipes wall as the result of chemical reactions. Because of these, an optimized chlorine dosing for the DWDS using model-based predictive control (MBPC) is developed through the steps of modelling the FCR transport along the main pipes of the DWDS, designing chlorine dosing and implementing a multiple-input multiple-output system control scheme in Matlab 7.0.1 software. Discrete time-space models (DTSM) that can be used to predict free chlorine residual (FCR) concentration along the pipes of the DWDS over time is developed using explicit finite difference method (EFDM). Simulations of the DTSM using step and rectangular pulse input show that the effect of water flow rate velocity is much stronger than the effect of chlorine effective diffusivity coefficient on the FCR distribution and decay process in the DWDS main pipes. Therefore, the FCR axial diffusion in single pipes of the DWDS can be neglected. Investigating the effect of injection time, initial chlorine distribution, and overall chlorine decay rate constant involved in the process have provided a thorough understanding of chlorination and the effectiveness of all the parameters. This study proposed a model-based chlorine dosing design (MBCDD) based on a conventional-optimum design process (CODP) (Aurora, 2004), which is created for uncertain water demand based on the DTSM simulation. / In the MBCDD, the constraints must be met by designing distances between chlorine boosters and optimal value of the initial chlorine distribution in order to maintain the controlled variable (CV), i.e. FCR concentration with a certain degree of robustness to the variations of water flow rate. The MBCDD can cope with the simulated DWDS (SDWDS) with the conditions; the main pipe is 12 inch diameter size with the pipe length of 8.5 km, the first consumers taking the water from the point of 0.83 km, the assumed pipe wall chlorine decay rate constant of 0.45 m/day, and the value of chlorine overall decay rate constants follow Rosman's model (1994), by proposing a set of rules for selecting the locations for additional chlorine dosing boosters, and setting the optimal chlorine dosing concentrations for each booster in order to maintain a relatively even FCR distribution along the DWDS, which is robust against volumetric water supply velocity (VWS) variations. An example shows that by implementing this strategy, MBCDD can control the FCR along the 8.5 km main pipe of 12 inch diameter size with the VWS velocity from 0.2457 to 2.457 km/hr and with the assumed wall and bulk decay constants of 0.45 and 0.55 m/day, respectively. An adaptive chlorine dosing design (ACDD) as another CODP of chlorine dosing which has the same concept with the MBCDD without the rule of critical velocity is also proposed in this study. The ACDD objective is to obtain the optimum value of initial chlorine distribution for every single change in the VWS. Simulation of the ACDD on the SDWDS shows that the ACDD can maintain the FCR concentration within the required limit of 0.2-0.6 mg/1. / To enable water quality modelling for studying the effectiveness of chlorine dosing and injection in the form of mass flow rate of pure gaseous chlorine as manipulated variable (MV), a multiple-input multiple-output (MIMO) system is developed in Simulink for Matlab 7.0.1 software by considering the disturbances of temperature and circuiting flow. The MIMO system can be used to design booster locations and distribution along a main pipe of the DWDS, to monitor the FCR concentration at the point just before injection (mixing) and between two boosters, and to implement feedback and open-loop control. This study also proposed a decentralized model-based control (DMBC) based on the MBCDD-ACDD and centralized model predictive control (CMPC) in order to optimize MV to control the CV along the main pipe of the DWDS in the MIMO system from the FCR concentration at just after the chlorine injection (CVin) to the FCR concentration (CVo) before the next chlorine injection with the constraints of 0.2-0.6 ppm for both the CVin and CVo. A comparison of the performances of decentralized PI (DPI) control, DMBC and CMPC, shows that the performances of the DMBC and CMPC in controlling the MIMO system are almost the same, and they both are significantly better than the DPI control performance. In brief, model-based predictive control (MBPC), in this case a decentralized model-based control (DMBC) and a centralized predictive control (CMPC), enable optimization of chlorine dosing for the DWDS.

Hydrogen peroxide and chlorine detection is critical for many biological and environmental applications. Hydrogen peroxide plays important roles in a variety of fields including plant physiology, medical, environmental and biochemical applications. Its role in plant defense and signal transduction, diseases such as Parkinson's and Alzhemier's, industrial processes such as disinfection and wastewater treatment and biochemical enzymatic reactions is critical. Given the gamut of areas that hydrogen peroxide is a key component of; its detection assumes great importance. Similarly chlorine has long been used as a disinfectant for making drinking water safe, but excessive chlorination is an environmental and health hazard in itself. In this work, micromachining techniques have been used to design, fabricate and test electrochemical sensors and microneedle structure that can be integrated for detection of hydrogen peroxide and free chlorine. A novel nanomaterial has been integrated with the hydrogen peroxide microsensor, which greatly increases the sensor lifetime and robustness. Miniaturization, low detection limits, high sensitivity and selectivity, as well as ease of fabrication are some of the other advantages of this work.