Document Type

Thesis - University Access Only

Award Date

2003

Degree Name

Master of Science (MS)

Department / School

Civil and Environmental Engineering

First Advisor

Delvin E. DeBoer

Abstract

The city of Sioux Falls, South Dakota had a need to investigate an alternative to their currently used preoxidant, potassium permanganate, as one of their preliminary treatment processes. The quality of their surface water source, the Big Sioux River, is substantially impacted by runoff, especially in the spring, which increases the turbidity and organic carbon in the water and subsequently escalates taste and odor problems. An alternative preoxidant suggested by the 200 l Master Plan (HDR Engineering, Inc. 200 l ), chlorine dioxide, was investigated and compared with potassium permanganate in this study. Bench-scale experiments provided an exploratory investigation of chlorine dioxide. The study was completed with the intention that if results of chlorine dioxide preoxidation appeared favorable, the city could then proceed with more extensive and costly pilot work with actual chlorine dioxide generators and continuously operated flowthrough systems. Potassium permanganate (KMnO4) has been the preferred preoxidant for surface water sources in the Midwest due to its many known treatment benefits. However, Sioux Falls currently feeds a large amount ofKMnO4, has frequent problems with the KMnO4 feeders, and would like to implement the use of an alternative chemical to reduce chemical feed problems, as well as to improve water quality. Chlorine dioxide (ClO2) may offer several advantages to a water treatment system. ClO2 has successfully oxidized taste and odor-causing compounds, decreased trihalomethane (THM) production, and inactivated Cryptosporidium. However, the use of ClO2 is not without constraints. Partial degradation of ClO2 to chlorite, which is regulated by the Disinfection/Disinfection Byproduct (D/DBP) Rule at 1.0 mg/L, occurs during the oxidation reaction and must be addressed when the application of ClO2 is considered. The objective ofthis exploratory research was to evaluate and compare the benefits of KMnO4 and ClO2 for preoxidation in order to determine which might be the better chemical for treatment of Big Sioux River water. Specific factors evaluated included impacts on taste and odor control, removal and nature of total organic carbon, coagulation, flocculation, sedimentation, oxidant demand, and THM production. The ClO2 decay and chlorite production kinetics were also investigated, as was the removal of chlorite using ferrous iron. Since a new pretreatment process, the Actiflo microsand ballasted clarification process, is currently under construction at the Sioux Falls Water Purification Plant, the impacts of this treatment unit also were ·considered. The effect of the injection point of ClO2 (prior to the Actiflo sedimentation system vs. postsedimentation) was addressed. The impacts of each treatment chemical were determined using bench-scale experiments, such as jar tests and simulated distribution system tests. Since treatment is affected by temperature and raw water quality, the testing plan was repeated during three periods - summer, fall/winter, and spring - to simulate several possible river conditions. The degradation of Cl02 was a rapid reaction that depended on water temperature. When evaluating the impact of order of chemical addition when both KMn04 and Cl02 were used, the addition ofKMn04 prior to Cl02 produced slightly less chlorite. In general, KMn04 appeared to be a better preoxidant for taste and odor control for Big Sioux River water. Cl02 did not appear to be an advantageous preoxidant for reduction of taste and odor. The specific taste and odor-causing compounds that exist in this water may not be amenable to Cl02 oxidation, since even at large doses of Cl02 a relatively strong odor still was detected. In some cases, KMn04 appeared to enhance flocculation, sedimentation, and filtration, but at excessive doses, settled and filtered water turbidities increased. In most cases, the addition of small doses of Cl02 appeared to have a minor effect on sedimentation and filtration. In general, the smallest dose of either preoxidant caused an increase in THM production. The THM production then decreased as the preoxidant dose was increased; however, the highest preoxidant dose usually created approximately the same amount of THM's as when no preoxidant was dosed at all, implying that the addition of a preoxidant would not decrease THM formation even if it is applied at high dosages. Reactions using ferrous iron were able to reduce chlorite to chloride. The simulated Actiflo treatment process decreased raw water odors according to one odor panelist and was able to remove total organic carbon (TOC) from the raw water. Results from tests to determine if Cl02 should be added before or after the simulated Actiflo process had conflicting results. The oxidant demand decreased slightly when Cl02 was added, whether it was before or after the simulated Actiflo process. THM formation was lower when Cl02 was added after the simulated Actiflo treatment process. Alternately, lower turbidity values were obtained from the simulated Actiflo process when Cl02 was dosed before the simulated Actiflo process. After treating the water with the simulated Actiflo process and elements of the full-scale treatment process (excluding KMn04 addition), reasonably low turbidity values were obtained. Sioux Falls personnel have indicated that KMn04 addition is not only for taste and odor control, but also to aid in the filterability of the water. Since the combination of the simulated Actiflo process and full-scale treatment process components was able to decrease odors and obtain relatively low turbidity values, perhaps with the implementation of Actiflo, KMnQ4 addition may no longer be necessary.

Library of Congress Subject Headings

Water -- Purification -- South Dakota -- Sioux Falls -- Evaluation.
Chlorine dioxide.
Potassium permanganate.

Publisher

South Dakota State University

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Rights Statement

In Copyright