Thesis (Ph. D.)--Michigan State University. Dept. of Civil and Environmental Engineering, 2006. / Title from PDF t.p. (viewed on June 19, 2009) Includes bibliographical references. Also issued in print.

abstract: Water quality is a severe problem throughout the world. Much available water is contaminated by pathogenic microbes. This project reviews the traditional process of solar water disinfection in bottles (SODIS), discusses experiments conducted with SODIS bottles modified to thermally enhance the process, analyzes experimental data for modified SODIS containers, and suggests ways that by which the traditional process can be improved. Traditional SODIS is currently used in many rural parts of developing countries to disinfect water. The process uses ultraviolet rays and thermal effects to inactivate microorganisms that tend to cause diarrheal disease. If a sufficiently high temperature is attained to reach a synergistic UV-thermal effect range, the process of SODIS is about three times faster. However, many factors can inhibit attainment of sufficient heating of water in SODIS bottles in practice. By modifying the bottles to enhance effectiveness of sunlight in increasing the temperature of the water, SODIS can be more effective. In this research, a series of experiments were conducted over a period of four months and15 days at Arizona State University Polytechnic campus in Mesa, Arizona, U.S.A. Four different types of inexpensive materials (black paint, white paint, foam insulation, and aluminized mylar) were used individually or in combination in seven different modified configurations to assess the potential of the modifications to increase the temperatures of water inside 2-liter PET bottles. Experiments were run in triplicate. Temperatures inside the bottles, along with yard temperature, were recorded over time. Graphs were plotted for each set of experiments. The results of these experiment show that several types of modifications increased water temperature during exposure to sunlight. Water in bottles with black paint and foam insulation on the back side attained the highest temperatures, approximately 8-10 degrees Celsius above temperatures attained in plain bottles. The results of these experiments show how several inexpensive, easily obtained materials can significantly enhance the SODIS process. / Dissertation/Thesis / M.S. Applied Mathematics 2011

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1992. / Vita. Abstract. Includes bibliographical references (leaves 63-65). Also available via the Internet.

In this work, electrophotocatalytic disinfection on selected microorganisms was verified. The electrophotocatalytic system allows the application of electrical bias to the photoanode coated with a titanium dioxide layer. The disinfecting effect was observed on E.coli and C.glabrata in aqueous solution. The effect of radiation intensity on electrophotocatalysis and selected optimal conditions for further experiments was observed in the E. coli organism. Photocatalytic disinfection was carried out under suitable conditions on C.glabrata yeast and the effect of sodium sulfate electrolyte on electrophotocatalytic disinfection was observed in this case.

>Magister Scientiae - MSc / Despite the wide success of antimicrobial agents against waterborne pathogens, waterborne disease continues to pose a threat to both mankind and animals. A major concern is that certain bacteria have developed resistance to antimicrobial agents, as a result of their overuse. Silver (Ag) nanoparticles are widely used for antibacterial purposes such as medical dressings. However, they are highly toxic to human cells. Hence, there is a great interest in developing next generation antibacterial nanoparticles that are as effective as Ag nanoparticles for antibacterial functions, while having less toxicity to human cells. Several methods can be used to generate these antimicrobial nanoparticles, one of which is green nanotechnology. Green nanotechnology uses natural plants such as tea to synthesise nanoparticles rather than chemicals, thus reduce human and animal harm and improve sustainability of antibacterial agents. Silver-titanium nano-composites (Ag-TiO2 NCs) were synthesised with the hydrothermal method using a tea extract from Aspalathus linearis (Rooibos, RB), and distilled water in the presence of nitrogen. The resulting structures were characterised with high resolution transmission electron microscopy (HRTEM), energy-dispersive spectroscopy (EDS) analysis X-Ray Diffraction (XRD) and Thermogravimetric Analysis (TGA). The antibacterial characteristics of these new NCs were evaluated against 3 bacteria: Bacillus cereus, Cupriavidus metallidurans, and Escherichia coli. The optimum processing conditions to produce 6-nm spherical NPs included maintaining the temperature at 90 °C, the pH at 4.35, and using RB extract at a concentration of 2 mg/mL. The size of silver NPs was reduced in acidic conditions, agglomerated in neutral conditions, and highly reduced in alkaline conditions. Increasing the pH decreased the particle size and narrowed the particle size distribution. Gram-positive B. cereus showed slight resistance or tolerance to the Ag-TiO2 nanocomposite compared to the gram-negative bacteria E. coli and C. metallidurans. The treatment concentration required for total inhibition of E. coli and C. metallidurans growth was 100 mg/mL. Supported silver nanoparticles has shown to be a suitable way to obtain highly dispersed silver over higher surface area. This approach allowed Ag-TiO2 nanocomposite to be an efficient bactericide, with less silver amount employed.

Photocatalytic oxidation is an alternative water treatment method under consideration for disinfecting water. Chlorine disinfection can form harmful byproducts, and some viruses (e.g. adenoviruses) are resistant to other alternative disinfection methods. Photocatalytic oxidation using nano-sized photocatalytic particles (e.g. TiO2, fullerene) holds promise; however, it is limited by its low efficiency and long required treatment times. This research focuses on improving virus inactivation by photocatalytic oxidation by modifying catalysts for improved activity, by analyzing virus inactivation kinetics, and by elucidating the inactivation mechanisms of adenovirus serotype 2 (AdV2) and bacteriophage MS2. Modifying TiO2 with silver (nAg/TiO2) or silica (SiO2-TiO2) improves the inactivation kinetics of bacteriophage MS2 by a factor of 3-10. nAg/ TiO2 increases hydroxyl radical (HO•) production while SiO2 increases the adsorption of MS2 to TiO2. These results suggest that modifying the photocatalyst surface to increase contaminant adsorption is an important improvement strategy along with increasing HO• production. The inactivation kinetics of AdV2 by P25 TiO2 is much slower than the MS2 inactivation kinetics and displays a strong shoulder, which is not present in the MS2 kinetics. nAg/TiO2 initially improves the inactivation rate of AdV2. SiO2-TiO2 reduces the AdV2 inactivation kinetics since adsorption is not significantly enhanced, as it is with MS2. Amino-C60 is highly effective for AdV2 inactivation under visible light irradiation, making it a good material for use in solar disinfection systems. The efficacy of amino-fullerene also demonstrates that singlet oxygen is effective for AdV2 inactivation. When exposed to irradiated TiO2, AdV2 hexon proteins are heavily damaged resulting in the release of DNA. DNA damage is also present but may occur after capsids break. With MS2, the host interaction protein is rapidly damaged, but not the coat protein. The kinetics of MS2 inactivation are rapid since it may quickly lose its ability to attach to host cells, while AdV2 kinetics are slower since the entire capsid must undergo heavy oxidation before inactivation occurs. Adenovirus inactivation likely occurs through breaching the capsid followed by radical attack of DNA and core proteins.

Photocatalytic oxidation is an alternative water treatment method under consideration for disinfecting water. Chlorine disinfection can form harmful byproducts, and some viruses (e.g. adenoviruses) are resistant to other alternative disinfection methods. Photocatalytic oxidation using nano-sized photocatalytic particles (e.g. TiO2, fullerene) holds promise; however, it is limited by its low efficiency and long required treatment times. This research focuses on improving virus inactivation by photocatalytic oxidation by modifying catalysts for improved activity, by analyzing virus inactivation kinetics, and by elucidating the inactivation mechanisms of adenovirus serotype 2 (AdV2) and bacteriophage MS2. Modifying TiO2 with silver (nAg/TiO2) or silica (SiO2-TiO2) improves the inactivation kinetics of bacteriophage MS2 by a factor of 3-10. nAg/ TiO2 increases hydroxyl radical (HO•) production while SiO2 increases the adsorption of MS2 to TiO2. These results suggest that modifying the photocatalyst surface to increase contaminant adsorption is an important improvement strategy along with increasing HO• production. The inactivation kinetics of AdV2 by P25 TiO2 is much slower than the MS2 inactivation kinetics and displays a strong shoulder, which is not present in the MS2 kinetics. nAg/TiO2 initially improves the inactivation rate of AdV2. SiO2-TiO2 reduces the AdV2 inactivation kinetics since adsorption is not significantly enhanced, as it is with MS2. Amino-C60 is highly effective for AdV2 inactivation under visible light irradiation, making it a good material for use in solar disinfection systems. The efficacy of amino-fullerene also demonstrates that singlet oxygen is effective for AdV2 inactivation. When exposed to irradiated TiO2, AdV2 hexon proteins are heavily damaged resulting in the release of DNA. DNA damage is also present but may occur after capsids break. With MS2, the host interaction protein is rapidly damaged, but not the coat protein. The kinetics of MS2 inactivation are rapid since it may quickly lose its ability to attach to host cells, while AdV2 kinetics are slower since the entire capsid must undergo heavy oxidation before inactivation occurs. Adenovirus inactivation likely occurs through breaching the capsid followed by radical attack of DNA and core proteins.

Thesis (Ph. D.)--Drexel University, 2004. / Includes abstract and vita. Includes bibliographical references (leaves 210-223).

>Magister Scientiae - MSc / Water is essential for life, yet access to safe drinking water is still a major concern worldwide due to waterborne diseases. The current study proposes silver nanoparticles (AgNPs) as an antibacterial agent. Silver nanoparticles were synthesised using different reductants and stabilisers, and the resulting structures were characterised with Ultra-violet visible (UV-vis) spectroscopy, transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS) analysis. The antibacterial properties of the AgNPs were tested against a panel of 5 indicator organisms: Cupriavidus metallidurans, Staphylococcus epidermidis, Mycobacterium smegmatis, Bacillus cereus and a multi-drug resistant Escherichia coli 1699. Spherical AgNPs that absorbed at around 400 nm, with diameters ranging between 18.8-26.4 nm or 5.4-13.1 nm were prepared by ascorbic acid or sodium borohydride respectively. The optimum processing conditions that produced 6±1.8 nm spherical nanoparticles included maintaining the temperature at 0 ⁰C, the pH at 9.78 and the NaBH4/Ag/PVP ratio at 16:1:10. Exposing AgNPs to light for 6 hours did not alter the particle size rather it changed the particles shape from spherical to icosahedral. Stirring caused particles to agglomerate, however, no agitation resulted in the formation of irregular structures of different sizes. Sensitivity to the AgNPs ranged between 25 % and 100 % reduced bacterial growth depending on the strains used and the concentration of the AgNPs. The Gram negative bacteria were more sensitive to AgNPs than Gram positive bacteria. However silver ions were more toxic than AgNPs for all but one of the strains tested, B. cereus was completely resistant to both Ag+ and AgNPs. C. metallidurans and E.coli (1699) showed a dose dependent sensitivity to AgNPs and the minimum inhibitory concentrations were established at 50 and 20 mg/L AgNPs respectively. C. metallidurans and E.coli (1699) were also eradicated by 10 mg/L Ag+. The E. coli TEM images showed accumulation of AgNPs within the cells, cell shrinking and leakage of cellular components. This suggests that AgNPs have a similar toxicity effect on bacterial cells as Ag+.

Métodos de desinfecção da água destinam-se à inativação de patógenos a fim de minimizar o risco de doenças transmitidas pela água. Estes métodos incluem tratamento com luz ultravioleta e processos químicos, para o qual cloro, dióxido de cloro, hipoclorito e ozônio são comumente utilizados. No entanto, métodos analíticos modernos revelam que estes métodos padrão de desinfecção da água podem levar à formação de produtos tóxicos e potencialmente cancerígenos. Desse modo, desenvolver métodos mais adequados para a desinfecção de água é uma necessidade. Inativação Fotodinâmica é uma nova abordagem para a eliminação de microrganismos patogênicos. Basicamente, esse processo utiliza fotossensibilizadores e luz para promover uma resposta fototóxica, normalmente oxidativa, capaz de danificar biomoléculas e estruturas celulares, provocando a morte dos microrganismos. No entanto, o fotossensibilizador não pode permanecer livre como um contaminante neste tipo de aplicação. Assim, o objetivo desse estudo foi o desenvolvimento de membranas de quitosana com fotossensibilizadores incorporados visando à desinfecção microbiológica da água. As membranas foram preparadas incorporando-se o azul de metileno, a rosa de bengala, meso-tetrakis (4-N-metilpiridil)-porfirina ou a 5,10,15,20-tetrakis(p-aminofenil)-porfirina. A eficiência do processo de Inativação Fotodinâmica com os fotossensibilizadores incorporados as membrana foi investigada empregando-se a bactéria Escherichia coli como modelo, já que esta bactéria está comumente presente em águas de abastecimento. Os resultados mostraram que, dentre os quatro fotossensibilizadores incorporados em membranas de quitosana, o processo fotodinâmico empregando a TMPyP se mostrou mais efetivo: 5 log de redução após 120 minutos de irradiação com LED branco e 4 log de redução após 120 e 140 minutos de irradiação com LED azul e amarelo, respectivamente. Além disso, com o intuito de simular uma situação real de desinfecção, um sistema circulatório de água, contendo membranas de quitosana/TMPyP reforçadas com nylon, foi empregado. Os resultados mostraram que o processo de fotoinativação dinâmico foi efetivo, apresentando 3 log de redução em 80 minutos de irradiação com LED branco. Estes resultados sugerem que o processo é efetivo para inativar bactérias contaminantes na água, empregando-se fotossensibilizadores incorporados em quitosana como suporte polimérico. / Methods of water disinfection aim to inactivate pathogens in order to minimize the risk of waterborne diseases. These methods include treatment with ultraviolet light and chemical processes, for which chlorine, chlorine dioxide, hypochlorite and ozone are commonly used. However, modern analytical methods reveal that these standard methods of water disinfection may lead to the formation of toxic and potentially carcinogenic products. Thus, developing suitable methods for water disinfection is a necessity. Photodynamic inactivation is a new approach to eliminate pathogenic microorganisms. Basically, this process uses photosensitizers and light to promote a phototoxic response, normally oxidative, capable of damaging biomolecules and cellular structures, causing the death of microorganisms. However, the photosensitizer cannot remain free as a contaminant in this type of application. The objective of this study was to develop chitosan membranes with incorporated photosensitizers aiming the microbiological water disinfection. The membranes were prepared by incorporating methylene blue, rose bengal, meso-tetrakis (4-N-methylpyridyl)-porphine or the 5,10,15,20-tetrakis(p-aminophenyl)- porphyrin. The efficiency of the Photodynamic Inactivation with photosensitizers incorporated into the membrane was investigated using the bacteria Escherichia coli as a model, since this bacteria is commonly present in drinking water. The results showed that, among the four photosensitizers incorporated into chitosan membranes, the process employing the TMPyP was more effective: 5 log reduction after 120 minutes of irradiation with white LED and 4 log reduction after 120 and 140 minutes of irradiation with blue and yellow LED, respectively. Moreover, in order to simulate a real situation of disinfection, a water circulation system, containing TMPyP/chitosan membranes reinforced with nylon, was employed. The results showed that the process of photoinactivation using a dynamic system was effective, with about 3 log reduction in 80 minutes of irradiation with white LED. These results suggest that the process is effective to inactivate bacterial contaminants in water using photosensitizers incorporated into chitosan as a polymeric support.