Dissertations / Theses on the topic 'Water purification disinfectant'

The aim of this study was to evaluate the effectiveness of water treatment processes of two drinking water plants to remove immunotoxins and steroid hormones. Raw and treated drinking water was screened for effects on inflammatory activity using the biomarker IL-6, humoral immunity using the biomarker IL-10 and cell mediated immunity using the biomarker IFN-&gamma
. In vitro human whole blood culture assays were used in order to elucidate potential immunotoxicity.

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.

Chloramine is a widely used alternative disinfectant for chlorine in potable distribution water. This alternative was investigated and employed to show its effect for suppressing coliforms, trihalomethanes(THMs), disinfection by-products (DBPs), and corrosivity.Coliform analyses were performed with m-Endo(total coliform) and m-T7 agar(injured coliform) by using a standard Membrane Filtration method. Heterotrophic bacteria were monitored with HPC agar(PCA) and R2A agar (nutrient limited agar). EPA methods 502.2, 524.2, and 504 were used to determine levels of Trihalomethanes(THMs) and Disinfection by-products(DBPs).In our study, we observed no significant differences in coliform counts, that could be attributed to the switch in disinfectant. The most common coliform identified was Enterobacter cloacae. We also noted that m-T7 performed better than m-Endo in the detection of coliforms. We also observed a low level of corrosion (0.4-3.8 mils/year) in the distribution system (DS). Higher counts of heterotrophic bacteria were enumerated on R2A when compared to HPC. DBP values decreased two fold when compared with DBP values for the two previous years during which chlorine was used as the disinfectant.
Department of Biology

Tap water collected according to standard methods was examined for microbial presence. Epifluorescent diagnoses using redox probe 5-cyano-2,3ditolyl tetrazolium chloride (CTC), 4',6-diamidino-2-phenylindole (DAPI), and acridine orange (AO) were employed for direct evidence of microorganisms. Evidence of total (DAPI or AO), respiring (CTC) bacteria, and heterotrophic plate count (HPC) was determined on multiple occasions during the summer, fall, and winter 1996-1997. Pseudomonas aeruginosa, Acinetobacter sp., Bacillus licheniformis, and Methylobacterium rhodinum were isolated and identified by the API and Biolog system using GN and GP procedures. On the basis of comparisons presented in this study between the CTC method and the standard HPC procedure, it appeared that the number of CTC-reducing bacteria in the tap water samples was typically higher than that determined by HPC, indicating that many respiring bacteria detected by the CTC reduction technique fail to produce visible colonieson the agar media used. In the seasonal data obtained by the CTC method, no difference was shown among respiring bacterial counts obtained from June through January. In the examination of P. aeruginosa viability in presence of chlorine, the number of CTC-positive bacteria exceeded the number of CFU by more than 2 logs after exposure to chlorine, suggesting that reliance on HPC overestimate the efficacy of disinfection treatment. In inactivation assays using the Biolog MT plate, no sensitivity to chlorine or chloramine disinfectants was noted even at high concentration levels (5 mg/liter). Following initial drop, bacterial activities increased as contact time increased. Thus, it appears that the MT microplate provides too low a cell concentration, too great a contact time, and/or too low a concentration of tetrazolium dye within the well for successful analysis of disinfectant capability to selected bacterial strains isolated from distribution water.
Department of Biology

Errata pasted onto front end-paper. Bibliography: leaves 113-120. To obtain robust and quantitative data on the influence of UV absorption and suspended solids on UV disinfection an experimental study using commercial disinfection technology was undertaken.

Water disinfection systems utilizing electrolytically generated copper:silver ions (200:20 to 400:40 ug/L) and low levels of free chlorine (0.1 to 0.4 mg/L) were evaluated at room (21-23°C) and elevated (39-40°C) temperatures in filtered well water (pH 7.3) for their efficacy in inactivating Legionella pneumophila (ATCC 33155). A contact time of 24 hr was necessary for copper:silver (400:40 ug/L) to achieve a 3 log₁₀ reduction in bacterial numbers at room temperature. As the copper:silver concentration increased to 800:80 ug/L (K = 7.50 x 10⁻³ log₁₀ reduction/min), the inactivation rate significantly (p ≤ 0.05) increased. In water systems at room temperature with and without copper:silver (400:40 ug/L), the inactivation rates significantly increased as the free chlorine concentration increased from 0.1 mg/L (K = 0.397 log₁₀ reduction/min) to 0.4 mg/L (K = 1.047 log₁₀ reduction/min). All disinfection systems, regardless of temperature or free chlorine concentration, showed increased inactivation rates when 400:40 ug/L copper:silver was added; however, this trend was significant only at 0.4 mg/L free chlorine.

The validation of UV reactors is currently accomplished by biodosimetry, in which the reactor is treated as a "black-box" and hence cannot account for the dependence of the dose delivery on the complex hydrodynamics and the spatial variation in UV intensity. Alternative methods, such as fluorescent microspheres as non-biological surrogates and computational fluid dynamics (CFD) simulations, have been developed; however, each method has its shortcomings. In this study, a novel technique for the spatial and temporal assessment of the hydrodynamics and the UV dose delivered and the link between these two factors in a lab-scale UV reactor using three dimensional laser induced fluorescence (3DLIF) is developed. This tool can also be utilized for the optimization of UV reactors and to provide data for validation of CFD-based simulation techniques. Regions of optimization include areas around the UV lamp where short-circuiting occurred, a longer inlet approach section that enhances the performance of the reactor by reducing short circuiting paths and a longer outlet region to provide greater mixing. 3DLIF allows real time characterization of mixing and dose delivery in a single lamp UV reactor placed perpendicular to flow by capturing fluorescence images emitted from a laser dye, Rhodamine 6G, using a high speed CCD camera. In addition to three-dimensional mixing, the technique successfully visualized the two-dimensional, transient mixing behaviors such as the recirculation zone and the von Karman vortices and the fluence delivery within the reactor, which has not been possible with traditional tracer test techniques. Finally, a decomposition technique was applied to the flow and fluence delivery based concentration data to reveal similar structures that affect these phenomena. Based on this analysis, changing the flow in the reactor, i.e. the Reynolds number, will directly affect the fluence delivery.

Les infeccions causades per Legionella són un greu problema de salut pública al nostre país. La majoria de casos esporàdics i de brots epidèmics es relacionen amb aigües de consum que han estat sotmeses a un o més processos de desinfecció. Tot i això, Legionella spp. no només és capaç de sobreviure a aquests tractaments sinó que es multiplica al llarg dels sistemes de distribució convertint-se en un risc ambiental. Els principals factors que afavoreixen la supervivència i multiplicació de Legionella als sistemes d’aigua resideixen en la pròpia biologia del bacteri, que ha demostrat en moltes ocasions ser resistent a condicions físico-químiques extremes, així com les interrelacions que estableix amb altres microorganismes com els protozous, amb els que comparteix hàbitat. Els protozous, i en concret les amebes de vida lliure dels gèneres Acanthamoeba o Hartmannella s’han descrit en els últims anys com habitants freqüents dels sistemes de distribució d’aigua. Aquestes sobreviuen a condicions adverses mitjançant la formació d’estructures de resistència anomenades cists. La font nutricional de les amebes són els bacteris els qual fagocita i digereix. Tot i això, alguns d’aquests bacteris han desenvolupat estratègies per sobreviure la digestió amebiana i no sols això sinó que com en el cas de Legionella, poden fins i tot aprofitar els resursos cèl•lula hoste per multiplicar-se. A més, en estat endosimbiont Legionella queda protegida de l’efecte de desinfectants fet que podria originar una ràpida recolonització dels sistemes d’aigua un cop acabats els tractaments de desinfecció. Tres dels desinfectants més utilitzats a nivell europeu per tractar l’aigua de consum són el clor, la temperatura i la radiació UV. Tot i que el seu ús està regulat en nombroses normatives estatals, aquestes s’apliquen sense tenir en compte les amebes de vida lliure i les interrelacions que aquestes poden tenir amb altres microorganismes. L’objectiu principal d’aquest treball va ser estudiar l’eficàcia d’aquests tres desinfectants de l’aigua aplicant les mateixes condicions d’estudi sobre Legionella spp.; amebes de vida lliure en els dos estats de vida, trofozoïts i cists; i sobre els simbionts que estableixen Legionella i Acanthamoeba. En primer lloc es van obtenir soques de Legionella spp., i amebes de vida lliure de diferents orígens, tant ambientals com de col•lecció i es van optimitzar els protocols de cultiu dels diferents microorganismes, especialment pel que fa a les amebes. A continuació es van posar a punt mètodes quantitatius que ens permetessin comparar la viabilitat cel•lular després de cada tractament amb els tres desinfectants. I es van establir les condicions d’assaig per a cada un dels desinfectants. Finalment es van establir co-cultius per observar si l’associació entre Legionella i Acanthamoeba modificava d’alguna manera l’eficàcia dels desinfectant envers aquests dos microorganismes. La formació de co-cultius i el seu monitoreig mitjançant la tècnica del FISH ens va permetre observar com la soca de Legionella passava d’un estat plactònic a un estat d’emdosimbiont a l’interior dels trofozoïts. Analitzant la susceptibilitat de les diferents soques de Legionella, d’amebes de vida lliure, tan en estat de trofozoït com de cist, així com de Legionella com a endosimbiont d’Acanthamoeba per cadascun dels tractaments aplicats, es van proposar diferents models per descriure’n la cinètica d’inactivació. A partir d’aquí els resultats obtinguts es van comparar amb altres estudis publicats i se’n van extreure unes conclusions finals. Els resultats mostraren que clor, temperatura i radiació UV tenen un efecte desinfectant diferent pel que fa a les diferents soques de Legionella i amebes de vida lliure. Les diferències observades entre els diferents tractaments poden ser atribuïbles a la concentració de desinfectant, el temps d’exposició i a les diferències intrínseques de cada soca per cada microorganisme utilitzat. Pel que fa a la susceptibilitat de les amebes, trofozoïts i cists es van comportar de maneres diferents, sent els trofozoïts més sensibles que els cists. Finalment, L. pneumophila va resultar ser més resistent als tractaments amb desinfectants aplicats associada a trofozoïts d’Acanthamoeba en comparació amb el bacteri en condicions axèniques. Per tant, a l’hora d’aplicar tractaments de desinfecció, cal tenir en compte la complexa ecologia de Legionella com a endosimbiont d’amebes perquè aquests siguin eficaços i evitar així processos de recolonització.
Legionella infections are serious problem which causes concern to health public services in our country. Despite all measures and controls realized, most sporadic cases and outbreaks have been related to drinking water systems that have been subjected to one or more disinfection processes. Legionella spp., not only survive these treatments but multiplied over the distribution system becoming a potential environmental hazard. The main factors that promote Legionella survival and proliferation in water systems are the bacteria biology itself, since Legionella is able to survive under a wide range of environmental conditions, as well as the relationship that Legionella establishes with other microorganisms that live in the same habitat as protozoa. Protozoa, and specifically free-living amoebae of the genera Acanthamoeba and Hartmannella have been described as common inhabitants of drinking water distribution systems. These amoebae survive in front harsh environmental conditions by forming resistant structures called cysts. Amoebae feed mainly on bacteria which are engulfed by phagocitosis and digested intracellularly. However, some of these bacteria have developed some strategies to survive amoebae digestion and some of them, as Legionella are able to use host cellular resources to multiply within it. In addition, as an endosimbiont, Legionella remains protected from disinfectants which could lead to a rapid recolonization of water distribution systems once disinfection treatments have been applied. Three of the most commonly used water disinfectants in Europe for drinking water treatment are chlorine, temperature and UV radiation. Although its use is regulated by many national guidelines, its efficacy relies mainly on bacterial inactivation without considering other microorganisms such as free living amoebae and its relationships with other microorganisms as Legionella. Therefore, the main objective of this work was to study the effectiveness of these three water disinfectants applying the same study conditions, on Legionella spp.; free-living amoebae considering its two life stages; and on the simbionts between Legionella and Acanthamoeba. First of all, several strains of Legionella spp., and free-living amoebae from different origins (environmental and from culture collections) were obtained and culture protocols were optimized, especially for free-living amoebae. Second, test conditions were established for each of the disinfectants and a quantitative method was implemented in order to compare cell viability after every disinfection treatment. Finally, to see whether the association between Legionella and Acanthamoeba modifies the effectiveness of the three disinfectants towards these two types of microorganisms, co-cultures of Legionella and Acanthamoeba were realized. Co-culture formation was monitored by using a FISH method, which led us observe how axenic Legionella changed to an intracellular state within Acanthamoeba trophozoites. Analyzing the susceptibility of the Legionella spp. strains; free-living amoebae strains, either trophozoites and cysts stages; as well as Legionella as an Acanthamoeba endosymbiont, for each of the treatments applied, inactivation kinetics models were proposed. Results obtained were compared with studies published by other authors and final conclusions were considered. Results showed that, chlorine, temperature and UV radiation have a disinfectant effect on the different Legionella strains used, as well as on free living amoebae. Differences on the disinfectant effect could be atributted to disinfectant concentration, exposure time and strain intrinsic characteristics. Regarding free living amoeba, trophozoites and cysts had a significantly different behaviour, being trophozoites more sensitive to disinfectants than cysts. Finally, L. pneumophila as and endosymbiont of amoeba strains showed a greater resistance to disinfectant compared with the axenic state. Because of that, when applying disinfections treatments, the complex ecology of Legionella as an amoeba endosymbiont should be considered in order to prevent a system recolonization.

In recent years, a compound N-nitrosodimethylamine (NDMA), a probable human carcinogen, has been identified as an emerging disinfection by-product (DBP) since its formation and detection were linked to chlorine-based disinfection processes in several water utilities in the U.S. and Canada. Numerous organic nitrogen compounds present in water may impact the formation of NDMA during disinfection. Amine-based water treatment polymers used as coagulants and flocculants have been suggested as potential NDMA precursors due to the presence of amine functional groups in their structures, as well as the possible presence of dimethylamine (DMA) residues in polymer products. To minimize the potential risk of NDMA associated with water treatment polymers, the mechanisms of how the polymers behave as NDMA precursors and their contribution to the overall NDMA formation under actual water treatment conditions need to be elucidated. This research involved a systematic investigation to determine whether amine-based water treatment polymers contribute to NDMA formation under drinking water and wastewater treatment conditions, to probe the involved reaction mechanisms, and to develop strategies to minimize the polymers NDMA formation potential. The investigation included five research tasks: (1) General screening of NDMA formation potential of commonly used amine-based water treatment polymers, (2) NDMA formation from amine-based water treatment polymers under relevant water treatment conditions, (3) Probing the mechanisms of NDMA formation from polyamine and PolyDADMAC, (4) Effect of water treatment processes on NDMA formation from amine-based water treatment polymers, and (5) Developing strategies to reduce polymers NDMA formation potential. Direct chloramination or chlorination of high doses of polymers in deionized water at longer than typical contact time was used in the general screening of the NDMA formation potential of water treatment polymers and in the studies to identify reaction mechanisms. On the other hand, realistic dosages of chloramines and polymers and contact time were used in simulating representative water treatment conditions to evaluate the contribution of polymers to the overall NDMA formation in real systems. On the basis of the study results, strategies were developed to reduce the NDMA formation potential of amine-based water treatment polymers, which include modification of polymer structures and treatment parameters.

Hydrodynamic behavior in reactors used for water treatment, particularly in ozone contactors with serpentine flow, is known to strongly affect the process efficiency. However, exact flow characteristics inside these reactors are not well understood, as traditional approach either considers these reactors as black box or relies on less accurate Reynolds-Averaged Navier-Stokes (RANS) simulation. In order to provide a deep understanding of the hydrodynamics and solute transport phenomena in these reactors, high resolution numerical studies using the Large Eddy Simulation (LES) method are performed. The reactor geometries investigated in this research are Constant Baffle Spacing Multi-Chamber (CBSMC) ozone contactors and a Variable Baffle Spacing ozone contactor Model (VBSM). The LES results in two multi-chamber ozone contactors (CBSMC -Normal-Width and -Half-Width) suggest that the flow through these reactors is characterized by the presence of extensive short-circuiting and large internal recirculation. The results also suggest that the flow is highly three dimensional with a pair of symmetric counter-rotating secondary vortices. LES studies based on VBSM, the baffle spacing of which varies between 0.5 times to 5 times the size of the base chamber; suggest that the width of the recirculation zone grows at about the same rate as the baffle spacing. Instantaneous turbulent eddies are prevalent in the chamber and increase turbulent mixing. The elevated levels of turbulence are found in the short-circuiting flow path. The tracer is dispersed along the short-circuiting path and strongly into the recirculation zone due to turbulent diffusion. Baffle spacing greater than the entrance gate height, but also smaller baffle spacing, worsens the disinfection efficiency. Finally, the turbulent Schmidt number of RANS simulation was investigated by employing the previously validated LES simulation. Due to the presence of very strong turbulent diffusion in the reactors, the turbulent Schmidt number is found out to be much less than the values commonly used, and is also specific to the baffle spacing.

A study was conducted to evaluate the sorption characteristics of six disinfection byproducts (DBPs) on four sorbents. To investigate sorption of volatile organic compounds (VOCs), specially designed experimental batch and continuous flow modules were developed. The investigated compounds included: chloroform, 1,2-dichloroethane (DCE), trichloroethylene (TCE), bromodichloromethane (BDCM), methyl tertiary butyl ether (MTBE), bromate and bromide ions. Sorbents used included light weight aggregate (LWA), an inorganic porous material with unique surface characteristics, Amberlite® XAD-16, a weakly basic anion exchange resin, Amberjet®, a strongly basic anion exchange resin, and granular activated carbon (GAC). Batch experiments were conducted on spiked Milli-Q® and lake water matrices. Results indicate considerable sorption of TCE (68.9%), slight sorption of bromate ions (19%) and no appreciable sorption for the other test compounds on LWA. The sorption of TCE increased to 75.3% in experiments utilizing smaller LWA particle size. LWA could be a viable medium for removal of TCE from contaminated surface or groundwater sites. Amberlite® was found unsuitable for use due to its physical characteristics, and its inability to efficiently remove any of the test compounds. Amberjet® showed an excellent ability to remove the inorganic anions (>99%), and BDCM (96.9%) from aqueous solutions but with considerable elevation of pH. Continuous flow experiments evaluated GAC and Amberjet® with spiked Milli-Q® and tap water matrices. The tested organic compounds were sorbed in the order of their hydrophobicity. Slight elevation of pH was observed during continuous flow experiments, making Amberjet® a viable option for removal of BDCM, bromate and bromide ions from water. The continuous flow experiments showed that GAC is an excellent medium for removal of the tested VOCs and bromate ion. Each of the test compounds showed different breakthrough and saturation points. The unique design of the continuous flow apparatus used in the study proved to be highly beneficial to assess removal of volatile organic compounds from aqueous solutions.

Orientador: Jose Euclides Stipp Paterniani
Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Civil
Made available in DSpace on 2018-08-02T03:02:10Z (GMT). No. of bitstreams: 1 Pires_MarcoRoberto_D.pdf: 5271302 bytes, checksum: 360fb9a15e870769155cec24f76d1dab (MD5) Previous issue date: 2002
Resumo: Desinfecção de esgotos com radiação ultravioleta vem sendo utilizado, principalmente, em países europeus e nos EUA. A fotorreativação dos microrganismos tem sido avaliada para determinar seu grau de interferência na desinfecção. Este trabalho teve como objetivo avaliar a radiação ultravioleta para diferentes qualidades de efluentes e estudar a fotorreativação. Foram utilizados dois reatores diferentes, sendo um com lâmpadas emersas e outro imersa. Os reatores foram testados em seis efluentes diferentes para quatro vazões diferentes para cada reator. Os coliformes totais e fecais foram analisados para avaliar a eficiência dos reatores. Ensaios de fotorreativação em condições controladas foram realizadas. De forma geral, o Reator I foi mais eficiente que o Reator TI, e a qualidade do efluente muitas vezes foi mais importante que a dose aplicada como apresentada no Ponto de Coleta 3 para coliformes fecais, em que a inativação foi maior para a vazão 4 (com menor tempo de exposição à luz) em vez de ocorrer para a vazão 1 (com maior tempo de exposição). Doses de radiação ultravioleta mais altas implicam em valores iniciais e finais de fotorreativação menores, porém para atingir o valor máximo necessita de mais tempo. Quanto maior a dose de radiação ultravioleta aplicada menor é o grau de fotorreativação; os coliformes totais tem melhor correlação para análises desta natureza quanto comparado com a E.co/i
Abstract: Disinfection of effluents with ultraviolet radiation has been used in Europeans countries and United States. The photoreactivation of microorganism have been estimated to determine the influence on the disinfection. The objective of this work had to evaluate the ultraviolet disinfection to different qualities of effluent and photoreactivation. Two different kinds of reactors were used in experimental analyzed. The reactors were tested to six different effluents for four flows. Total and fecal coliforms were analyzed to estimate the efficiency of reactors. Assays of photoreactivation were analyzed in controlled conditions. In most of case, the Reactor I was more efficient than Reactor II, and effluent quality was more important than the dose uv applied. Dose uv higher imply in initial and final values of lower photoreactivation. The total coliforms have better correlation than E.coli
Doutorado
Saneamento e Ambiente
Doutor em Engenharia Civil

Disinfection by-products (DBPs) are a major group of water contaminants and their role in causing adverse health outcomes, including adverse pregnancy outcomes, endocrine disruption, respiratory related adverse health outcomes and cancer has been subject to extensive epidemiological and toxicological research and review. Determination of safe exposure to DBPs, particularly within drinking water supplies, has been a topic of extensive debate, with a wide range of acceptable levels set across the industrialized world. The focus of the research in this thesis was on two of the main health outcomes associated with DBP exposure, namely adverse pregnancy outcomes and asthma related symptoms. To assess adverse pregnancy outcomes in Perth, an extensive classification quantification of the major DBPs in Perth drinking water was conducted. A registrybased prevalence study was carried out to assess birth defects in relation to high, medium and low DBP areas (defined by the water sampling and analysis). It was found that women living in high THM areas are 22% (odds ratio (OR) 1.22, 95% confidence interval (95% CI) 1.01-1.48) more likely of having a baby with any birth defect. High exposure was also strongly associated with an increased risk of having a baby with a cardiovascular defect (62% increased risk). Low birth weight and prematurity were also assessed; however these outcomes were not associated with an increased risk through an increase in exposure. Following on from this analysis, a population risk assessment model was developed for DBPs in high exposure environments. This involved a three step process: (i) Firstly a questionnaire-based validation and reliability study was used to assess water consumption patterns of a population of pregnant women in Perth. (ii) Secondly a prediction model for teratogenic burden of DBPs in Perth was developed, related to the exposure patterns of the population of pregnant women involved in the validation and reliability study. (iii) Finally, combining the information collected in (i) and (ii), along with the regression slope estimates for birth weight from the prevalence study (defined in Section 2.2.1), a dose-response model for THMs and birth weight was developed. Predictive simulations for birth weights at given THM levels were then conducted. It was estimated that pregnant women in Perth are exposed to between 0.3 – 4.10 µg/day ingested TTHM, and of this, the more toxic brominated forms accounted for between 0.27 – 3.69 µg/day. Based on a dose-response model used, birthweights calculated for the ‘hypothetical’ exposures ranged from 3403.2g for the highest exposure to 3503.5g in the lowest exposure, which is a difference of over 100g. Although the resulting reduction in birth weight is not extreme, there is still a significant reduction in birth weight present as exposure to TTHMs increases. This is the first doseresponse model to be developed to assess an adverse pregnancy outcome based on pregnant women exposure data, and will be a useful tool for assessing varying exposures throughout not only Australia but also throughout the industrialised world, where DBP exposure is highly prevalent.

An increase in the number of bacteria resistant to most of the antibiotics or biocides in common use is a problem faced by industries and the community at large. More bacteria are resistant to moderate levels of biocides, with the bacteria in biofilms being the most difficult to control. High levels of biocides are used and this has detrimental effects on the environment, as biocides are toxic to humans, being carcinogenic, corrosive and producing intolerable odours. Electrochemical activation technology provides an alternative way of controlling microorganisms. ECA water was shown in other countries to have antimicrobial properties. Anolyte, the positively charged solution is benign to fumes and corrosion caused by other biocides. Since anolyte is eco-friendly and present no problems to the environment, it provides a good alternative for controlling microorganisms instead of chemical control. The minimum inhibitory concentration (MIC) of anolyte and its antimicrobial properties against different microorganisms in suspension was evaluated. The I: 1 0 and neat anolyte gave a 100% kill of all organisms tested while 1 :20 dilution gave variable killing percentages ranging from 31 % to 100%. Minimum inhibitory concentration was found to be 20% for most Gram positives and 50% for most Gram negatives. Anolyte did have some antimicrobial properties with MIC differing amongst different organisms. Biofilm control using different concentrations of anolyte and sodium hypochlorite was evaluated. Neat and 1: 10 anolyte removed biofilm while 1: 100 did not have effect on biofilm. The 100 and 300 ppm sodium hypochlorite were effective in removing the biofilm while 10, 25 and 50 ppm could not remove it. Hand wash trials and hospital disinfection using anolyte resulted in a decrease in the number of cfu/25cm3 after treatment. Effective disinfection of hands and hospital equipment was achieved. Different surfaces in a milking parlour were treated with anolyte to test its suitability to disinfect a milking parlour. High numbers of microorganisms and spreaders were observed from the plates before the surfaces were cleaned with anolyte. All spreaders were identified as sporeformers. Results were generally better when anolyte was used as a disinfectant, being able to eliminate spreaders as well. Treatment of chicken carcasses with anolyte to evaluate its effect on their shelf life was also tested. The number of colony forming units on chicken carcasses decreased after treatment of the carcasses with anolyte. Anolyte is therefore a naturally safe disinfectant that could be used in most fields including water distribution systems and industries for biofilm control, hospitals for minimising cross infection, food industries for increasing quality and shelf life of food and also in households for washing hands.
Dissertation (MSc (Microbiology))--University of Pretoria, 2006.
Microbiology and Plant Pathology
unrestricted

The removal of microbial populations from potable water has been a practice with great importance towards public health, as it has resulted in the reduction of literally millions of cases of infectious disease. In the United States, pathogenic organisms are most commonly removed from drinking water through the application of chlorine. Ninety-nine per cent of all U.S. potable water treatment facilities that disinfect, rely on chlorine as their sole or primary disinfectant, and over 175,000,000 Americans regularly consume chlorinated water. In 1974, Rook and Bellar et al. published studies which indicated that chlorine reacted with organic matter in water during treatment to produce a wide-range of halogenated by-products. Since that time, numerous analyses have been performed to isolate and identify the by-products of chlorination. Toxicologic and epidemiologic studies have been performed, some of which suggest that the use of chlorine as a disinfectant may be contributing to the incidence of chronic disease in the United States. Because of the concern that the use of chlorine for potable water disinfection may be contributing to chronic disease, Amendments to the Safe Drinking Water Act (SDWA) have been promulgated which strictly regulate disinfectants and disinfection by-products. Future disinfectant and disinfectant by-product regulations (1992) will have a major impact on the purveyors of potable water in the U.S.. Probably the largest challenge U.S. water treatment utilities now face is in the attempt to control for disinfectants and disinfectant by-products while maintaining the microbiological integrity of the water supply. The SDWA Amendments and their supporting regulations will result in major changes in the way water quality parameters are measured, and the way disinfection and treatment strategies are practiced. This thesis looks closely at the role of chlorine as a disinfectant, the by-products arising from chlorine reacting with organic matter, as well as the rationale behind the disinfectant and disinfectant by-product regulations. After examining the chemical, toxicologic and epidemiologic evidence which fueled the new SDWA regulations, available treatment strategies for meeting the new regulations will be detailed and examined. A water treatment strategy which best appears to maximize the reduction of waterborne disease and minimize the risk of chronic disease will then be offered.
Graduation date: 1992