Call number: LD2668 .T4 1960 G35

Electroporation is the process where externally applied electric fields cause significantly increased permeability of the cell membrane. The increased permeability allows the transport of external compounds into the cell. This is important for applications in electrochemotheropy, electrofusion and drug delivery. Electroporation also has applications in the disinfection of liquids. Given a high enough electric field across the cell membrane, the electroporation process can become irreversible, leading to cell destruction. With the cell membrane under an intense electric field, the cell membrane structure fails causing the cell to die. Conventional liquid beverage disinfection systems rely on slow heating methods requiring large power requirements; this can reduce the taste and quality of some liquids. Pulse generators provide the necessary electric fields to produce the required voltage potential across the cell membrane. The usefulness of electroporation depends on several parameters such as amplitude, frequency and rise/fall times of the electric field. The wave shape also has a bearing on performance, and is limited by the pulse generator topology. A multilevel bipolar waveform is desired with operating frequencies above about 1 kHz. The cascaded H-bridge or full-bridge topology is the most useful as it capable of producing multilevel bipolar waveforms at high frequency. This thesis presents the design and implementation of a multilevel high-voltage pulse generator, capable of creating very high-voltage AC pulses. MOSFET switching devices in conjunction with good layout practices were used to provide required fast switching speeds. The full-bridge topology is used to create a multilevel output profile through cascading of multiple stages. As a full-bridge topology inherently creates a RCL resonant network, there are many challenges associated with mitigating high-frequency noise sources. Two separate stages are built, a low voltage stage capable of outputting up to 200 Vp and a high voltage stage capable of switching up to 1 kVp. A control board was also built for pulse signal generation and user configuration of the output waveforms. The designed pulse generator can produce short pulses of up to 1.4 kVp at frequencies of up to 350 kHz using primarily resistive loads (that simulate a conductive liquid load). Little high frequency switching noise was observable on the output waveform. A single stage pulse generator was also tested with actual liquid loads using an electrode chamber, demonstrating electroporation. The liquid load testing was performed on water and milk derived from milk powder. Results showed that the liquid loads were consistent with primarily resistive loads.

The search for alternative water disinfectants to those commonly used, such as chlorine, probably began when the disadvantages of those disinfectants became known. Soluble disinfectants have short half-lives and need to be replenished periodically which requires monitoring the determination of appropriate concentrations for waters being treated. This disadvantage may be balanced by the ability to alter dose concentrations of soluble disinfectants to meet changes in demands. Maintenance of a residual disinfectant concentration which can act throughout a water distribution system is another advantage of soluble disinfectants. Disadvantages due to reaction of organic materials include the loss of disinfecting capability, health hazards related to the disinfectant and the potential loss of aesthetic water qualities such as taste, smell and color. The purpose of this study was to investigate different surface contact disinfectants which, while having an inflexible dose concentration capability and releasing no residual disinfectant concentration, do not require monitoring and do not significantly leach into the waters they contact. Powdered aluminum when mixed with a loamy sand reduces virus concentration 3-4 orders of magnitude better than controls while not significantly altering the pH or aluminum concentration of waters that pass through the soil columns. Labeled poliovirus 1 was found to adsorb onto the aluminum surface in batch experiments and undergo degradation or dissociation of the capsid proteins with release of viral fragments and clumps within 76 hours. Freon dispersion of the viral clumps showed the clumps to be non-infective. Polyacrylamide gel electrophoresis of poliovirus 1 incubated with aluminum for 76 hours suggested degradation or dissociation of viral capsid proteins 1, 2 and 3. Magnesium peroxide and magnesium oxide, while effectively inactivating viruses, significantly increase the pH of water which they contact. Polyhalex resin and I5 resin reduce virus concentration, but release functional groups into the surrrounding water. Contact disinfectants such as aluminum, may find point-of-use application for drinking water, use in septic tank leachfields or sewage treatment infiltration basins to reduce the threat of spreading potential disease-causing organisms.

The integration of photocatalytic advanced oxidation into solar disinfection is a robust method of improving the microbial and chemical quality of treated water. This study evaluates the performance of photocatalytic solar irradiated batch reactors through an analytical model that reduces treatment parameters by simplifying photoreactor geometry and relating performance to reactor configuration. Accompanying experiments compare the performance of titanium dioxide coated foams of varying pore size to suspended and fixed film configurations through degradation of organic dyes (acid orange 24 and methylene blue), Escherichia coli, and 1,4-dioxane. Results indicate that a catalyst immobilized on a foam support can match the performance of a suspension due to effective mass transport and association between analyte and foam. Additionally, the potential treatment capacity of solar photocatalysis was compared to conventional treatment methods. Results of this comparison stress the fundamental limitation of solar photocatalysis if visible light wavelengths are not harnessed.

The integration of photocatalytic advanced oxidation into solar disinfection is a robust method of improving the microbial and chemical quality of treated water. This study evaluates the performance of photocatalytic solar irradiated batch reactors through an analytical model that reduces treatment parameters by simplifying photoreactor geometry and relating performance to reactor configuration. Accompanying experiments compare the performance of titanium dioxide coated foams of varying pore size to suspended and fixed film configurations through degradation of organic dyes (acid orange 24 and methylene blue), Escherichia coli, and 1,4-dioxane. Results indicate that a catalyst immobilized on a foam support can match the performance of a suspension due to effective mass transport and association between analyte and foam. Additionally, the potential treatment capacity of solar photocatalysis was compared to conventional treatment methods. Results of this comparison stress the fundamental limitation of solar photocatalysis if visible light wavelengths are not harnessed.

This thesis examines the development and use of environmental health indicators for epidemiology, risk assessment and policy applications from a geographical perspective. Although indicators have traditionally been used to examine temporal trends, the development of environmental health indicators (EHIs) may enable comparisons to be made between areas with contrasting environmental health conditions, support efforts to highlight ‘hot spots’ and facilitate the analysis of spatial patterns in environmental health conditions and health risk. The use of environmental health indicators is relatively new and little research has been conducted in this area. In the light of this, this thesis examines EHIs in the context of contemporary developments in environmental indicators, health-related and quality of life indicators, and indicators of sustainable development. Essential characteristics and requirements for EHIs are identified and the main areas of application are discussed. In the second part of the thesis, the development and use of Effis for evaluating exposure to traffic-related air pollution is examined, using GIS techniques. Potential indicators of exposure are identified and these are applied at a range of spatial scales, along with a number of additional measures. The results of this exercise show that although exposure to traffic-related air pollution is both difficult and costly to evaluate, proxy measures may be used. Pollutant concentrations, for example are frequently used to assess exposure, yet the lack of suitable data may also frequently preclude their use. Whilst other, cruder measures may be used, the relationship between these indicators, measured concentration and exposure is often uncertain. Consequently, EHIs for exposure to traffic-related air pollution may not provide a reliable indication of exposure and health risk. Their use in this area should therefore be undertaken with great caution and attempts made to validate specific measures prior to their use. At the same time, however, coarser ‘upstream’ indicators may provide relevant information in a policy context. For use in highlighting areas of concern, raising awareness about environmental health issues and encouraging policies which aim to improve environmental health conditions, ease of data collection and relation to policy may be more important than relation to specific health effects

This research focused on chlorine-free disinfection of wastewater by complying with today's regulations. The equipment used was a continuous flow electrochemical reactor connected to an alternating current (AC) power supply. The electrodes used were made out of titanium coated with iridium oxide. To determine the inactivation of Escherichia Coli, a bacterial count method based on the USEPA method 1603 was used. After several experiments it was determined that electrochemical disinfection using AC was not efficient and economic enough to be classified as a viable alternative to chlorine disinfection. It was demonstrated that chlorine can be produced by electrolysis using AC and that no hydrogen could be noticed as a byproduct of the electrolysis of wastewater. When the results from this investigation were compared to the ones obtained using DC in Acosta (2014), it was determined that the belief that AC and DC are equally efficient at disinfecting wastewater is wrong.

Research on electrochemical disinfection of municipal wastewater has been conducted at the University of New Orleans using a continuous flow electrochemical reactor connected to a direct current (DC) power supply changing its polarity and varying the electrode distance. Bacterial inactivation and chlorine production were the main parameters that were recorded. After months of research, it was determined that the electrochemical disinfection reactor is efficient and has a great potential for the future. There is no need to use chlorine and it has low operation costs. The following design recommendations for an electrochemical disinfection unit were given: A detention time of 5 +- 0.3 minutes A minimum volumetric current density of 1000 amps/m3 A minimum detention current density of 80 amps.hr/m3 The combination of the three recommended design values yielded excellent disinfection efficiencies and low chlorine production.

>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.

As dificuldades do reprocessamento dos endoscópicos gastrointestinais, o risco de contaminação e os casos de infecções representam desafios amplamente conhecidos na comunidade cientifica. Neste sentido, investigou-se o reprocessamento de endoscópios gastrointestinais subsidiado nos níveis de sujidade, contaminação microbiana e presença de biofilme. Trata-se de um experimento laboratorial realizado em três fases por meio da bioluminescência com adenosina trifosfato (ATP) para avaliação do nível de sujidade; polimerase chain reaction (PCR) para carga bacteriana e cultura microbiana para determinação do nível de contaminação. Ainda, avaliou-se as superfícies internas de canais de endoscópios por microscopia eletrônica de varredura (MEV) quanto à presença de biofilme. A análise estatística dos dados foi subsidiada em medidas de tendência central, testes de Man-Whitney, Wilcoxon e Spearman, p<0,05, por meio do software IBM SPSS Statistics versão 23.0. A avaliação de 99 endoscópios antes e após limpeza manual demonstrou a eficácia do processo na redução de sujidade (p<0,001) e contaminação microbiana (p=0,03), inclusive com baixo percentual da amostra com micro-organismos viáveis. Dos 75 endoscópios avaliados após o reprocessamento evidenciou-se uma redução do nível de sujidade (todos com <50URL, interna e externamente); entretanto a presença de carga bacteriana foi de 3log de bactéria/mL e 10,6% de positividade das culturas. Os micro-organismos isolados dos lavados de endoscópios após o reprocessamento foram Staphylococcus aureus, Staphylococcus epidermidis, Staphylococcus hominis, Staphylococcus capitis, Roseomonas gilardii e Micrococcus luteus. Na avaliação dos canais de biópsia de endoscópios provenientes do Brasil observou-se maior contaminação do que os da Austrália (p<0,001). Todos os canais apresentaram biofilme e danos em suas superfícies, entretanto as amostras brasileiras apresentaram particularidades, como, presença de hemácias, neutrófilos e fungos. Assim, observou-se que apesar da baixa carga microbiana nos endoscópios há o risco potencial de infecção cruzada associado ao biofilme, ameaçando a qualidade e segurança do reprocessamento. Adiciona-se a necessidade de avanços tecnológicos e científicos contra o biofilme na prática do reprocessamento de endoscópios / The difficulties on gastrointestinal endoscope reprocessing, contamination risk and outbreaks are a recognized challenge in science. It was investigated gastrointestinal endoscope reprocessing for dirtiness, contamination level and presence of biofilm. Laboratorial experiment performed in three phases using adenosine triphosphate (ATP) bioluminescence for dirtiness evaluation; polymerase chain reaction (PCR) for bacterial load and microbial culture for contamination level evaluation. In addition, it was evaluated biofilm on endoscope channels internal surfaces by scanning electron microscopy (SEM). Statistics analysis was performed by descriptive analysis, ManWhitney, Wilcoxon and Spearman tests, p<0,05, using IBM SPSS Statistics versão 23.0. Before and after cleaning analysis of 99 endoscopes showed it efficacy on reducing dirtiness (p<0,001) and microbial contamination level (p=0,03), including a small percentage of culturable microorganism. From 75 endoscopes tested after reprocessing demonstrated dirtiness level reduction (all samples <50RUL, from internal and external area); but, also, presence of bacterial load of 3 log of bacteria/mL and 10,6% of culture positive. The microorganisms isolated from endoscope flush after reprocessing were Staphylococcus aureus, Staphylococcus epidermidis, Staphylococcus hominis, Staphylococcus capitis, Roseomonas gilardii and Micrococcus luteus. Endoscope biopsy channel analysis showed that samples from Brazil had higher contamination level than the ones from Australia (p<0,001). All channels analyzed presented biofilm and damage on their surfaces, however Brazilian samples showed particularities, like, blood cells, neutrophils and fungus. So, ever with low microbial load on endoscopes there is a potential risk of crossinfection associated with biofilm, compromising reprocessing quality and safety. Additionally, there´s the need of scientific and technologic improvement on endoscope reprocessing against biofilm