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The monitoring of pH and free chlorine concentration in drinking water is important for water safety and public health. However, existing laboratory-based analytical methods are laborious, inefficient, and costly. This thesis focuses on the development of an easy-to-use, sensitive, and low-cost drinking water quality monitoring system for pH and free chlorine. An inkjet printing technology with a two-step thermolysis process in air is developed to deposit palladium/palladium oxide (Pd/PdO) films as potentiometric pH sensing electrodes. The redox reaction between PdO and hydronium ions generates the sensor output voltage. A large PdO percentage in the film provides a high sensitivity of ~60 mV/pH. A defect-free Pd/PdO film with small roughness contributes to a fast response and a high stability. When the Pd ink is thermalized in low vacuum, the deposited Pd/PdO film shows a bilayer structure. The residual oxygen in the low vacuum environment assists the decomposition of organic ligands for Pd to form a thin and continuous layer beneath submicron Pd aggregates. The oxidized bilayer film behaves as a temperature sensor with a sensitivity of 0.19% resistance change per °C, which can be used to compensate the sensed pH signals. Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is drawn by hand to form a free chlorine sensor. Free chlorine oxidises PEDOT:PSS, whose resistivity increment indicates the free chlorine concentration in the range of 0.5-500 ppm. Also, we simplified an amperometric free chlorine sensor based on amine-modified pencil leads. The simplified sensor is calibration-free, potentiostat-free, and easy-to-use. The pH, temperature, and free chlorine sensors are fabricated on a common substrate and connected to a field-programmable gate array board for data processing and display. The sensing system is user-friendly, cheap, and can accurately monitor real water samples. / Thesis / Doctor of Philosophy (PhD) / Sensitive, easy-to-use, and low-cost pH and free chlorine monitoring systems are important for drinking water safety and public health. In this thesis, we develop an inkjet printing technology to deposit palladium/palladium oxide films for potentiometric pH sensors and resistive temperature sensors. The different electrical and electrochemical properties of the palladium/palladium oxide films are realized by creating different film morphologies using different ink thermolysis atmospheres. The developed pH and temperature sensors are highly sensitive, fast in response, and stable. For free chlorine sensors, a hand drawing process is used to deposit poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate), which is an indicator for the free chlorine concentration over a wide range. We also developed a calibration-free free chlorine sensors based on modified pencil leads. Such a free chlorine sensor is integrated with the pH and temperature sensors, and an electronic readout system for accurate on-site drinking water quality monitoring at low cost is demonstrated.

Disinfectants are added to the water distribution system and swimming pools to control the growth of pathogenic microorganisms in water. High disinfectant levels are health hazards since they produce disinfectant by-products which are carcinogens. Thus, monitoring the amount ofresidual disinfectants present and maintaining an optimal amount of residual disinfectants throughout the distribution network is very crucial for safe water distribution. Colorimetric measurements are the current standard for measuring disinfectant levels in water. However, it is very difficult to integrate colorimetric measurements into automated monitoring devices. Redox active molecules like the phenyl-capped aniline tetramer (PCAT) can be incorporated as a dopant into a single wall carbon nanotube sensor for detecting oxidant in drinking water. The sensor works on the principle of oxidizing adsorbed redox molecules on carbon nanotubes by oxidant present in drinking water thus changing the resistivity of the carbon nanotube film. Most commonly used disinfectants are HOCl, Cl2, ClO2, Chloramine, KMnO4, HOBr, H2O2, O3, Br2, I2, etc. They all are oxidizing agents and can be distinguished from one another as they have different oxidation potentials. For water treatment purposes, it is not enough to know the disinfectant level, but it is also very important to identify which disinfectant is present. Currently, there is no standard method for distinguishing different disinfectants presents in water. The development of sensor arrays based on redox active molecules having different redox potentials is a potential pathway towards differentiating between different disinfectants in water. Different aniline oligomers were synthesized to create a library of redox active molecules. Redox properties of these molecules have been determined, and expected results were compared with the sensor performance. In the future, these sensors can be incorporated into a reliable, resettable and reagent free sensor array for monitoring and distinguishing different disinfectants in water. Being able to constantly monitor the disinfectant level and identifying the disinfectant present in water will enable us to design an improved and sustainable disinfecting system. / Thesis / Master of Science (MSc)

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The presence of postharvest sanitizers has shown to be an effective approach to reducing microbial cross contamination in agricultural washing operations. However, choosing an appropriate sanitizer can be challenging due to produce commodity, processing conditions and interference with organic load. Current research shows a wide variety of methods to mimic the organic load of vegetable processing conditions, with paddle mixing and blender as the most commonly used. Controlling and understanding the physiochemical properties of wash water is key in maintaining sanitizer efficacy. The effects of simulated wash water preparation method on the physiochemical properties were tested at 0 and 50 COD(mg/L) and no significant difference was observed. However, at high levels of organic load results showed a significant difference between turbidity values at 1,500 COD. Free residual chlorine titration methods were compared, using DPD-titrimetric and Iodometric method. Results showed a significant difference between titration methods in organic load heavy environments. Commercially available chlorine based sanitizers, Pure Bright™ Germicidal Bleach and Clorox® Germicidal Bleach, were compared to a concentrated solution of sodium hypochlorite. Pure Bright™ Germicidal Bleach showed to perform the best by reducing 7 log CFU/ml of E. coli O157:H7 after 30 seconds in no organic load environments, whereas Clorox Germicidal bleach was able to reduce 7 log CFU/ml of E. coli O157:H7 after 30 minutes. These studies aim to provide best management practices for small in medium growers in the implementation of antimicrobial solutions for the maintenance of water quality in postharvest washing solutions.

O objetivo do presente estudo foi o de avaliar a influência da associação dos tensoativos cetrimida 0,2%, cetrimida 0,1% e cloreto de benzalcônio 0,008% aos hipocloritos de sódio e de cálcio 2,5% nas propriedades de pH, quantidade de cloro livre, tensão superficial, ângulo de contato, dissolução pulpar e atividade antimicrobiana. O pH e a concentração de cloro ativo foram avaliados por pHmetro digital e pela titulação, respectivamente. A tensão superficial foi mensurada através da técnica do anel de platina com um tensiômetro de Du Noüy. O ângulo de contato das soluções em bases de dentina humana foi aferido pelo software Drop Shape Analyzer. Para a análise da dissolução pulpar foram utilizados fragmentos de polpas bovinas e os resultados foram expressos por percentual de perda de massa. A atividade antimicrobiana frente ao Enterococcus faecalis foi realizada pelo método de difusão em Ágar. Os resultados mostraram que a associação de tensoativos aos hipocloritos de sódio e cálcio não alterou as propriedades de pH, cloro livre e dissolução pulpar das soluções. O hipoclorito de cálcio apresentou o maior valor de tensão superficial (72,13 ± 1,82 mN/m). Quando associados aos tensoativos, os hipocloritos de sódio e cálcio tiveram uma redução significativa da tensão superficial. O mesmo foi observado para o ângulo de contato. Os tensoativos apresentam atividade antimicrobiana. A associação dos hipocloritos à cetrimida 0,2% ou 0,1% aumentou o halo de inibição frente ao Enterococcus faecalis. Concluiu-se que a associação de tensoativos não modificaram as propriedades de pH, cloro livre e dissolução pulpar dos hipocloritos de sódio e cálcio 2,5%. Porém, ela foi capaz de diminuir a tensão superficial e o ângulo de contato das soluções. Ainda, a associação da cetrimida 0,2% e 0,1% melhorou a capacidade antimicrobiana dos hipocloritos. / The aim of this study was to evaluate the influence of surfactants 0,2% or 0,1% cetrimide or 0,008% benzalkonium chloride on 2.5% sodium and calcium hypochlorite in the properties of pH, free chlorine content, surface tension, contact angle, pulp dissolution and antimicrobial activity. The pH and free chlorine content were evaluated by digital pHmeter and by titration, respectively. Surface tension was measured by the platinum ring technique with a Du Noüy tensiometer. Solution’s contact angle in human dentin surfaces was checked by Drop Shape Analyzer software. Bovine pulps were used for pulp dissolution analysis and the dissolving capacity was expressed by percentual weight loss. Antimicrobial activity over Enterococcus faecalis was evaluated through the ágar diffusion method. The surfactants association on sodium and calcium hypochlorites did not alter pH, free chlorine content and pulp dissolution properties. Calcium hypochlorite had the higher surface tension (72,13 ± 1,82 mN/m). However, when sodium and calcium hypochlorite were associated to surfactants, a significant reduction of surface tension occured. The same was observed for contact angle analysis. The surfactants used in this study have antimicrobial activity. The association of 0,2% or 0,1% cetrimide enhanced antimicrobial activity of both hypochlorites. It was possible to conclude that surfactants association did not alter pH, free chlorine content and pulp dissolution properties of 2,5% sodium and calcium hypochlorite. It was capable to reduce surface tension and contact angle of the solutions. Moreover, the 0,2% or 0,1% cetrimide association increased antimicrobial activity of hypochlorite.

O objetivo do presente estudo foi o de avaliar a influência da associação dos tensoativos cetrimida 0,2%, cetrimida 0,1% e cloreto de benzalcônio 0,008% aos hipocloritos de sódio e de cálcio 2,5% nas propriedades de pH, quantidade de cloro livre, tensão superficial, ângulo de contato, dissolução pulpar e atividade antimicrobiana. O pH e a concentração de cloro ativo foram avaliados por pHmetro digital e pela titulação, respectivamente. A tensão superficial foi mensurada através da técnica do anel de platina com um tensiômetro de Du Noüy. O ângulo de contato das soluções em bases de dentina humana foi aferido pelo software Drop Shape Analyzer. Para a análise da dissolução pulpar foram utilizados fragmentos de polpas bovinas e os resultados foram expressos por percentual de perda de massa. A atividade antimicrobiana frente ao Enterococcus faecalis foi realizada pelo método de difusão em Ágar. Os resultados mostraram que a associação de tensoativos aos hipocloritos de sódio e cálcio não alterou as propriedades de pH, cloro livre e dissolução pulpar das soluções. O hipoclorito de cálcio apresentou o maior valor de tensão superficial (72,13 ± 1,82 mN/m). Quando associados aos tensoativos, os hipocloritos de sódio e cálcio tiveram uma redução significativa da tensão superficial. O mesmo foi observado para o ângulo de contato. Os tensoativos apresentam atividade antimicrobiana. A associação dos hipocloritos à cetrimida 0,2% ou 0,1% aumentou o halo de inibição frente ao Enterococcus faecalis. Concluiu-se que a associação de tensoativos não modificaram as propriedades de pH, cloro livre e dissolução pulpar dos hipocloritos de sódio e cálcio 2,5%. Porém, ela foi capaz de diminuir a tensão superficial e o ângulo de contato das soluções. Ainda, a associação da cetrimida 0,2% e 0,1% melhorou a capacidade antimicrobiana dos hipocloritos. / The aim of this study was to evaluate the influence of surfactants 0,2% or 0,1% cetrimide or 0,008% benzalkonium chloride on 2.5% sodium and calcium hypochlorite in the properties of pH, free chlorine content, surface tension, contact angle, pulp dissolution and antimicrobial activity. The pH and free chlorine content were evaluated by digital pHmeter and by titration, respectively. Surface tension was measured by the platinum ring technique with a Du Noüy tensiometer. Solution’s contact angle in human dentin surfaces was checked by Drop Shape Analyzer software. Bovine pulps were used for pulp dissolution analysis and the dissolving capacity was expressed by percentual weight loss. Antimicrobial activity over Enterococcus faecalis was evaluated through the ágar diffusion method. The surfactants association on sodium and calcium hypochlorites did not alter pH, free chlorine content and pulp dissolution properties. Calcium hypochlorite had the higher surface tension (72,13 ± 1,82 mN/m). However, when sodium and calcium hypochlorite were associated to surfactants, a significant reduction of surface tension occured. The same was observed for contact angle analysis. The surfactants used in this study have antimicrobial activity. The association of 0,2% or 0,1% cetrimide enhanced antimicrobial activity of both hypochlorites. It was possible to conclude that surfactants association did not alter pH, free chlorine content and pulp dissolution properties of 2,5% sodium and calcium hypochlorite. It was capable to reduce surface tension and contact angle of the solutions. Moreover, the 0,2% or 0,1% cetrimide association increased antimicrobial activity of hypochlorite.

O objetivo do presente estudo foi o de avaliar a influência da associação dos tensoativos cetrimida 0,2%, cetrimida 0,1% e cloreto de benzalcônio 0,008% aos hipocloritos de sódio e de cálcio 2,5% nas propriedades de pH, quantidade de cloro livre, tensão superficial, ângulo de contato, dissolução pulpar e atividade antimicrobiana. O pH e a concentração de cloro ativo foram avaliados por pHmetro digital e pela titulação, respectivamente. A tensão superficial foi mensurada através da técnica do anel de platina com um tensiômetro de Du Noüy. O ângulo de contato das soluções em bases de dentina humana foi aferido pelo software Drop Shape Analyzer. Para a análise da dissolução pulpar foram utilizados fragmentos de polpas bovinas e os resultados foram expressos por percentual de perda de massa. A atividade antimicrobiana frente ao Enterococcus faecalis foi realizada pelo método de difusão em Ágar. Os resultados mostraram que a associação de tensoativos aos hipocloritos de sódio e cálcio não alterou as propriedades de pH, cloro livre e dissolução pulpar das soluções. O hipoclorito de cálcio apresentou o maior valor de tensão superficial (72,13 ± 1,82 mN/m). Quando associados aos tensoativos, os hipocloritos de sódio e cálcio tiveram uma redução significativa da tensão superficial. O mesmo foi observado para o ângulo de contato. Os tensoativos apresentam atividade antimicrobiana. A associação dos hipocloritos à cetrimida 0,2% ou 0,1% aumentou o halo de inibição frente ao Enterococcus faecalis. Concluiu-se que a associação de tensoativos não modificaram as propriedades de pH, cloro livre e dissolução pulpar dos hipocloritos de sódio e cálcio 2,5%. Porém, ela foi capaz de diminuir a tensão superficial e o ângulo de contato das soluções. Ainda, a associação da cetrimida 0,2% e 0,1% melhorou a capacidade antimicrobiana dos hipocloritos. / The aim of this study was to evaluate the influence of surfactants 0,2% or 0,1% cetrimide or 0,008% benzalkonium chloride on 2.5% sodium and calcium hypochlorite in the properties of pH, free chlorine content, surface tension, contact angle, pulp dissolution and antimicrobial activity. The pH and free chlorine content were evaluated by digital pHmeter and by titration, respectively. Surface tension was measured by the platinum ring technique with a Du Noüy tensiometer. Solution’s contact angle in human dentin surfaces was checked by Drop Shape Analyzer software. Bovine pulps were used for pulp dissolution analysis and the dissolving capacity was expressed by percentual weight loss. Antimicrobial activity over Enterococcus faecalis was evaluated through the ágar diffusion method. The surfactants association on sodium and calcium hypochlorites did not alter pH, free chlorine content and pulp dissolution properties. Calcium hypochlorite had the higher surface tension (72,13 ± 1,82 mN/m). However, when sodium and calcium hypochlorite were associated to surfactants, a significant reduction of surface tension occured. The same was observed for contact angle analysis. The surfactants used in this study have antimicrobial activity. The association of 0,2% or 0,1% cetrimide enhanced antimicrobial activity of both hypochlorites. It was possible to conclude that surfactants association did not alter pH, free chlorine content and pulp dissolution properties of 2,5% sodium and calcium hypochlorite. It was capable to reduce surface tension and contact angle of the solutions. Moreover, the 0,2% or 0,1% cetrimide association increased antimicrobial activity of hypochlorite.

No description available.