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The removal of inorganic contaminants is a primary concern in drinking water treatment. Fluoride and arsenic both naturally occur in ground and surface waters throughout the world. Recent health concerns regarding extended exposure to high levels of fluoride in drinking water have prompted the United States Environmental Protection Agency (USEPA) to review the fluoride maximum contaminant level (MCL). Arsenic is one of the most well-known and toxic inorganic contaminants regulated by the USEPA. While typically associated with groundwater, arsenic could be an increasing concern for surface water sources in the future. Small water systems may not have the resources to adjust their treatment scheme to accommodate a lower fluoride MCL or target arsenic removal. In this study, enhanced alum coagulation was investigated as a treatment strategy for both fluoride and arsenic. Facilities with surface water sources face a particular challenge, as the presence of natural organic matter (NOM) may interfere with the removal of fluoride and/or arsenic during coagulation. This work builds upon previous investigation of the interactions between fluoride, NOM, and aluminum during coagulation by comparing two pilot studies in Texas and Colorado. Each pilot study confirmed that enhanced alum coagulation was able to remove fluoride during continuous flow experiments using natural source water; the comparison of the studies revealed that source water composition impacts the maximum efficacy of alum coagulation for fluoride removal. A higher influent organic concentration appears to reduce the maximum efficacy of fluoride removal. However, the use of pH control may also be a contributing factor to the discrepancy in fluoride removal between pilot studies. The pilot study with a lower maximum fluoride removal had a higher influent DOC concentration, but was run without pH control. Synthetic water jar testing confirmed the ability of alum coagulation to remove arsenic (V). A maximum arsenic removal of 99% was observed for As(V) at alum doses of 100 mg/L and above, and an alum dose of 20 mg/L achieved an As(V) removal of 97%. Aluminum residuals suggest that the presence of As(V) lowers the point of zero charge for aluminum hydroxide solid.
The definitive work on Dissolved Air Flotation Systems (DAF) for clarification of drinking water Dissolved Air Flotation for Water Clarification is a complete design and application source for the water industry divided into three parts: The first develops a fundamental basis for understanding how the process works, and might be adapted to work better. The second provides a reference for design engineers, water operators, and water managers regarding applications where DAF might be incorporated in an overall treatment scheme. The third develops the necessary DAF design concepts and to illustrate them by description of practical applications. Using DAF to remove particles is not only an important process for conventional drinking water plants, but may also be used as a pre-treatment process in membrane plants including reverse osmosis for water desalinization, and in water reuse applications. Dissolved Air Flotation for Water Clarification offers: Information on new applications of DAF in advanced water treatment, desalinization, water reuse, and industrial treatment in food, waste, and pulp and paper Detailed examples, including the world’s largest new DAF plant ever built – Croton, NY water treatment plant A single volume entirely devoted to DAF for drinking water clarification Coverage of conventional and pre-treatment processes SI and conventional units throughout
Coagulation and Flocculation in Water and Wastewater Treatment provides a comprehensive account of coagulation and flocculation techniques and technologies in a single volume covering theoretical principles to practical applications. Thoroughly revised and updated since the 1st Edition it has been progressively modified and increased in scope to cater for the requirements of practitioners involved with water and wastewater treatment. A thorough gamut of treatment scenarios is attempted, including turbidity, color and organics removal, including the technical aspects of enhanced coagulation. The effects of temperature and ionic content are described as well as the removal of specific substances such as arsenic and phosphorus. Chemical phosphorus removal is dealt with in detail, Rapid mixing for efficient coagulant utilization, and flocculation are dealt with in specific chapters. Water treatment plant waste sludge disposal is dealt with in considerable detail, in an Appendix devoted to this subject. Invaluble for water scientists, engineers and students of this field, Coagulation and Flocculation in Water and Wastewater Treatment is a convenient reference handbook in the form of numerous examples and appended information.
The dissolved air flotation (DAF) has been used in drinking water treatment for its excellent algae and natural organic matter (NOM) removal. DAF drinking water treatability test are often conducted in a DAF jar test apparatus. Although, DAF jar test studies showed that they were able to predict NOM removals at full-scale facilities well, they have not always been successful in predicting the turbidity removals. One possible reason of the DAF jar test inaccuracy results could be associated to the small jar diameter, which may create wall effects. Therefore, the first two objectives of this research are: a) to develop and test a new, larger diameter and larger volume batch bench-scale dissolved air flotation system (LB-DAF) to better simulate turbidity removals in drinking water applications; b) to confirm these results by comparing the LB-DAF and full-scale DAF turbidity removals for two other source waters. The raw water characteristics of the three plants were quite different and the testing was performed at different times of the year. The development/optimization of the LB-DAF evaluated the impact of different variables (i.e., mixing intensity, water depth/tank diameter ratio, impeller shape, saturator pressure and recycle ratio). The results showed that the LB-DAF predicted well the full-scale DAF turbidity removals at three water treatment plants, and these predictions were better than those of DAF jar tests. For the LB-DAF design and operational variables evaluated had a limited impact on the turbidity removals. The LB-DAF predicted well DAF full-scale turbidity removals regardless of water temperature. This is an indication of the robustness of the DAF system. Ballasted sedimentation (BS) is a compact coagulation/flocculation and sedimentation process combination that has become very popular because it is very compact and because it can handle large variations in raw water turbidity and NOM. The literature survey did not initially identify studies on the BS treatment of algal impacted waters, for which DAF is considered particularly suitable. Thus, the third main objective of this dissertation was to compare the efficiency of BS with that conventional gravity settling (CGS), and that of DAF for the treatment of an algal impacted water via jar tests. These comparisons were performed at the Belleville Water Treatment Plant using Bay of Quinte water, one of the most eutrophic zones of Lake Ontario. Unfortunately, a change of weather prior to the testing resulted in raw water samples with relatively low concentrations of algae and cyanobacteria. The testing showed that DAF and BS had very similar NOM, cyanobacteria/algae (chlorophyll a and phycocyanin) removals.; however, the BS required microsand addition, polymer addition and a slightly higher alum dose. Only for turbidity removal the DAF was somewhat superior. It is suggested that these comparison experiments be repeated with waters that are more impacted by algae and cyanobacteria.
The problem of reservoir eutrophication and resulting increase of algal activity is common for seven Dutch waterworks. In this context, the text investigates dissolved air flotation (DAF) as an alternative for algae removal, compared to conventionally applied sedimentation.