Hydrogen sulfide imparts odors and taste to drinking water and can be corrosive to distribution systems. Groundwater sources used to produce drinking water tend to have sulfide concentrations ranging from below 0.1 to over 3 mg/L. Under anaerobic conditions, hydrogen sulfide can be formed from reduction of sulfate and elemental sulfur through chemical or biological reactions. Therefore, to decrease the potential for hydrogen sulfide in water systems, control of all forms of sulfur should be consistent. Hydrogen sulfide in groundwater can be controlled through conversion or removal mechanisms. Conversion reactions result from chemical or biological reactions that oxidize hydrogen sulfide to elemental sulfur or sulfate, depending on the reaction conditions. Removal reactions include stripping, anion exchange, or formation of a precipitate that can be removed through solid/liquid separation processes. In many groundwater treatment systems, hydrogen sulfide is controlled through aeration, chlorine oxidation, or a combination of these two methods. In addition to chlorine, other oxidizers can be used including hydrogen peroxide, UV, ozone, or potassium permanganate. The main factors that influence whether hydrogen sulfide is oxidized to elemental sulfur and/ or sulfate are pH, temperature, and the type and dose of oxidant. In recent years alternative treatments technologies such as anion exchange, have become available. It is interesting to note that this technology was proposed as early as the middle of last century. Although large scale anion exchange has not been implemented, its application for the removal of hydrogen sulfide is feasible based on anion exchange principles. This research was designed to evaluate feasible options for controlling hydrogen sulfide from groundwater sources. The feasibility of using anion exchange was investigated through pilot-scale testing of four groundwater sources. In addition, the performance of typical and alternative chemical oxidizers to control hydrogen sulfide was evaluated.

Water supply systems aim, among other objectives, to protect public health by reducing the concentration of, and potentially eliminating, microorganisms pathogenic to human beings. Yet, because water supply systems are engineered systems facing variable conditions, such as raw water quality or treatment process performance, the quality of the drinking water produced also exhibits variability. The reliability of a treatment system is defined in this context as the probability of producing drinking water that complies with existing microbial quality standards. This thesis examines the concept of reliability for two physicochemical treatment technologies, conventional rapid granular filtration and ultrafiltration, used to remove the protozoan pathogen Cryptosporidium parvum from drinking water. First, fault tree analysis is used as a method of identifying technical hazards related to the operation of these two technologies and to propose ways of minimizing the probability of failure of the systems. This method is used to compile operators’ knowledge into a single logical diagram and allows the identification of important processes which require efficient monitoring and maintenance practices. Second, an existing quantitative microbial risk assessment model is extended to be used in a reliability analysis. The extended model is used to quantify the reliability of the ultrafiltration system, for which performance is based on full-scale operational data, and to compare it with the reliability of rapid granular filtration systems, for which performance is based on previously published data. This method allows for a sound comparison of the reliability of the two technologies. Several issues remain to be addressed regarding the approaches used to quantify the different input variables of the model. The approaches proposed herein can be applied to other water treatment technologies, to aid in prioritizing interventions to improve system reliability at the operational level, and to determine the data needs for further refinements of the estimates of important variables.

Research has shown biological filtration can be a successful treatment for manganese (Mn) removal from groundwater and surface water. In this study, bench-scale direct biofiltration was used to remove Mn and dissolved organic carbon (DOC) from a pH 6 surface water source in Halifax, Canada. The removal of Mn in pH 6 surface water was significantly (? = 0.05) removed with 200-300 µg/L phosphorus (P), and 500 µg/L hydrogen peroxide (H2O2). DOC removal was significantly (? = 0.05) improved with granular activated carbon (GAC) media, P enhancement at 200-300 µg/L, and H2O2 enhancement at 500 µg/L. Mn was likely removed by biological oxidation and physical adsorption to biogenic Mn and iron (Fe) oxides. These results show direct biofiltration of surface water at pH 6 can remove Mn below the 50 µg/L aesthetic guideline from a Mn loading of over 1 mg/L. Further research is required to verify the microbial mechanism.

The ability of six types of granular activated carbon (GAC) to quench H2O2 was evaluated by bench-scale H2O2 decomposition kinetics tests and pilot-scale H2O2 breakthrough tests. Bench-scale studies showed that carbon ageing significantly reduced the performance of H2O2 quenching by the GAC, but that the greatest impacts occurred within the first 25 000 bed volumes of water treated, with performance tending to stabilize afterwards. Pilot-scale studies suggested that both H2O2 exposure and exposure to natural organic matter were important factors in GAC ageing, with exposure to oxygen also suspected of being important. A continuously stirred tank reactor (CSTR)-in-series model was proposed for the prediction of H2O2 breakthrough in a GAC column.

The ability of six types of granular activated carbon (GAC) to quench H2O2 was evaluated by bench-scale H2O2 decomposition kinetics tests and pilot-scale H2O2 breakthrough tests. Bench-scale studies showed that carbon ageing significantly reduced the performance of H2O2 quenching by the GAC, but that the greatest impacts occurred within the first 25 000 bed volumes of water treated, with performance tending to stabilize afterwards. Pilot-scale studies suggested that both H2O2 exposure and exposure to natural organic matter were important factors in GAC ageing, with exposure to oxygen also suspected of being important. A continuously stirred tank reactor (CSTR)-in-series model was proposed for the prediction of H2O2 breakthrough in a GAC column.

Point-of-use (POU) and point-of-entry (POE) water treatment are forms of decentralized water treatment that are becoming increasingly sought alternatives for ensuring the safety of drinking water. Although the acceptance of POU and POE systems is still the subject of some debate, it is generally acknowledged that they have a role to play in drinking water treatment. However, some of the main drivers for the increase in the use of POU and POE alternatives include: (1) the emergence of new technologies with high removal efficiencies of target contaminants; (2) the enhanced certification system of POU and POE treatment devices and components which ensures that devices have been well engineered to achieve defined contaminant removal targets and do not add contaminants from materials of construction; (3) the inclusion of POU and POE systems as acceptable means to comply with drinking water standards; and (4) the concerns voiced by consumers in several surveys regarding the safety of centrally treated drinking water; which, regardless of whether or not these concerns are justified, have led to an increase in the use of POU and POE treatment systems. With the commercialization of these devices the task of selecting a suitable device for treatment has become cumbersome. When the inherent complexity of a particular drinking water treatment task is added to the mix, a complex decision making situation is created. Thus the need for designing a decision support tool to compare and select POU and POE treatment systems was evident. Currently the best decision aid for selecting POU and POE systems is NSF International’s listing of the devices and their contaminant reduction claims. A significant contribution of this research is the depiction of an appropriate conceptual framework for developing usable and valid decision support systems (DSSs) to select or design water or wastewater treatment systems. A thorough investigation of the methods used to develop DSSs benchmarked a systematic approach to developing DSSs, which includes the analysis of the treatment problem(s), knowledge acquisition and representation, and the identification and evaluation of criteria controlling the selection of optimal treatment systems. Finally, it was concluded that there is a need to develop integrated DSSs that are generic, user-friendly and employ a systems analysis approach. Another significant contribution of this research is applying a systems analysis approach to outline aspects of implementation, management, and governance of POU and POE water treatment systems. The analysis also included a timeline of the progress of POU and POE treatment from regulatory, industry and certification, and research perspectives. Results of the analysis were considered the first step of a conceptual framework for the sustainability assessment of POU and POE treatment systems which acts as the basis for developing a decision support system that will help select sustainable POU or POE treatment systems. In the context of POU and POE treatment, sustainability encompasses providing: (a) safe drinking water to help maintain good human health and hygiene; (b) minimum negative impact on the environment; (c) better use of human, natural, and financial resources; (d) a high degree of functional robustness and flexibility; and (e) cultural acceptance thus encouraging responsible behavior by the users. The most significant contribution of this research is developing, for the first time, a set of sustainability criteria, objectives, and quantifiable indicators to properly assess the sustainability of the various POU and POE alternatives. Twenty five quantitative and qualitative indicators covering technical, economic, environmental, and socio-cultural aspects of implementing a POU or a POE system were defined. Results of a survey of experts’ judgment on the effectiveness of the developed list of indicators generated 52 comments from 11 experts, which helped in refining and enhancing the list. The conceptual framework for assessing the sustainability of POU and POE systems represented a blueprint for building the decision support system. Decision logic and cognitive thinking was used to formulate the calculation of the 20 refined indicators. The Analytical Hierarchy Process (AHP), a recognized Multi-criteria Decision Analysis (MCDA) tool, was employed to construct the structural hierarchy of sustainability indicators. Pairwise comparison was used to help in the analysis of indicators' relative importance and develop the indicators’ weights. A survey was designed to develop the relative weights of the indicators based on the average response of 19 stakeholders to a series of pairwise comparison questions pertaining to the relative importance of the indicators. Finally, the practical contribution of this research is the development of, for the first time, a new Decision Support System for Selecting Sustainable POU and POE Treatment Systems (D4SPOUTS) suitable for a particular water treatment case. The MCDA technique explained above is combined with designed screening rules, constraints, and case characteristics to be applied to a knowledgebase of POU and POE treatment systems incorporated in the DSS. The components of the DSS were built using Microsoft® Excel® and Visual Basic® for Applications. The quality of the DSS and aspects of its usability, applicability, and sensitivity analysis are demonstrated through a hypothetical case study for lead removal from drinking water. This research is expected to assist water purveyors, consultants, and other stakeholders in selecting sustainable and cost effective POU and POE treatment systems.

The monitoring of water distribution systems (WDSs) has been a very popular subject of study since the terrorist attacks of September 11, 2001, and the subsequent passing of laws motivating the study of WDS monitoring to provide system protection in the event of a terrorist attack. Inhibiting many WDS monitoring studies to date is the large amount of computational expense required to conduct meaningful studies, especially for larger WDSs that are of most interest. In this study, methods were developed to determine the "importance" of WDS nodes in being considered as locations for sensors used to monitor a WDS in order to make sensor placement optimization more efficient. Single-objective protection goals considered individually in optimization were maximizing detection likelihood, minimizing expected detection time, and minimizing expected contaminated demand volume. A multiobjective protection goal accounting for all three single-objective goals concurrently was also considered; the formulation of the multiobjective optimization problem was intended to minimize tradeoffs among individual protection goals. Sensor placement optimization was carried out with the Iterative Subset Search Method (ISSM) employing genetic algorithms developed in this work; ISSM used nodal importance rankings to search a small subset of nodes for the optimal solution initially then broadened the search incrementally until convergence to a best solution occurred. To demonstrate the effectiveness of the methods developed, sensor placement was performed according to each of the protection goals for three study systems--one small and two large--and a variety of attack conditions. Desirable sensor node solutions that provided for significant protection were found in all cases, and in many cases sensor placement results were comparable to or better than those of other works. Nodal importance narrowed the search for optimal sensor nodes to a relatively small proportion of WDS nodes in most cases.

Water supply systems aim, among other objectives, to protect public health by reducing the concentration of, and potentially eliminating, microorganisms pathogenic to human beings. Yet, because water supply systems are engineered systems facing variable conditions, such as raw water quality or treatment process performance, the quality of the drinking water produced also exhibits variability. The reliability of a treatment system is defined in this context as the probability of producing drinking water that complies with existing microbial quality standards. This thesis examines the concept of reliability for two physicochemical treatment technologies, conventional rapid granular filtration and ultrafiltration, used to remove the protozoan pathogen Cryptosporidium parvum from drinking water. First, fault tree analysis is used as a method of identifying technical hazards related to the operation of these two technologies and to propose ways of minimizing the probability of failure of the systems. This method is used to compile operators’ knowledge into a single logical diagram and allows the identification of important processes which require efficient monitoring and maintenance practices. Second, an existing quantitative microbial risk assessment model is extended to be used in a reliability analysis. The extended model is used to quantify the reliability of the ultrafiltration system, for which performance is based on full-scale operational data, and to compare it with the reliability of rapid granular filtration systems, for which performance is based on previously published data. This method allows for a sound comparison of the reliability of the two technologies. Several issues remain to be addressed regarding the approaches used to quantify the different input variables of the model. The approaches proposed herein can be applied to other water treatment technologies, to aid in prioritizing interventions to improve system reliability at the operational level, and to determine the data needs for further refinements of the estimates of important variables.

Thesis (PhD.(Medical Virology)--Faculty of Health Sciences)-University of Pretoria, 2007. / Includes bibliographical references.

Neste projeto de pesquisa avaliou-se a etapa de filtração no processo de tratamento de água para abastecimento público. Para isto, foi utilizado um sistema de filtração piloto composto por quatro filtros rápidos por gravidade de camada profunda. Os filtros piloto foram alimentados com água decantada da Estação de Tratamento de Água Rio Grande, e operados com taxa de filtração de 500 m3/m2/dia. A concepção dos filtros variou em termos de material filtrante (areia e antracito), diâmetro dos grãos e altura do leito. Os filtros foram avaliados em termos de turbidez, contagem de partículas, evolução de perda de carga e velocidade ascensional de água de lavagem. Na Etapa 1, operando-se filtros de areia e antracito com diferentes diâmetros, o filtro de antracito com 1,3 mm de diâmetro e 120 cm de altura apresentou melhor comportamento no tocante aos parâmetros avaliados. Na etapa 2, comparando-se filtros de areia e de antracito com mesmo diâmetro (1,3 mm) e altura de leito (120 cm), mais uma vez o filtro de antracito foi superior. Acredita-se que os índices físicos justifiquem esse comportamento. Na Etapa 3, conclui-se que o aumento de altura de leito dos filtros de areia (1,3 mm) e antracito (1,3 mm) de 120 cm para 160 cm foi benéfico para ambos os materiais filtrantes em termos de qualidade do efluente, mas muito mais significativo para o antracito, e não se observou alteração de comportamento no tocante à evolução de perda de carga. Com o ensaio de fluidificação e expansão do leito filtrante, conclui-se que, considerando-se o mesmo tempo de duração da lavagem e a mesma expansão do leito, o filtro de antracito possibilitou a utilização de menor velocidade ascensional de água de lavagem, que representa grande economia com relação aos custos do sistema de lavagem. Assim, em todos os aspectos estudados, o uso de antracito (1,3 mm) como material filtrante para filtros rápidos por gravidade de camada profunda se mostrou mais vantajoso. / This project researched the filtration stage in the water treatment process for public use. The research used a pilot filtration system based on four rapid gravity depth bed filters, with a filtration rate of 500m3/m2/dia. The water used in the experiment came from sedimentation tank of the Rio Grande water treatment facility. During the experimental phase the filters were loaded with different depth, used different filter media (sand and anthracite) and used grain with different effective size. The filters were evaluated in terms of turbidity, particle count, head loss and superficial velocity of backwashing water. In the first part of the study, when analyzing the results of filters loaded to a depth of 120 cm using both sand and anthracite with different size, the anthracite filter with effective size of 1.3 mm was the one with the best results. In the second part of the study, when comparing anthracite and sand with same the effective size, the anthracite also presented better results. Finally when increasing the depth of the filter, both sand and anthracite filters showed improved performance in terms of effluent quality, but anthracite filters kept outperforming sand filters. In both case, there were no evidences of changing in the head loss development. When performing fluidization and expansion experiments, considering the same backwashing cycle time and expansion of filter media, the anthracite filter allowed lower superficial velocity which represents relevant economies in the washing system costs. Therefore the use of anthracite (1.3mm) as a filter medium for rapid gravity depth bed filters is recommended.