Document Type

Thesis - University Access Only

Award Date

2012

Degree Name

Master of Science (MS)

Department / School

Civil and Environmental Engineering

First Advisor

Delvin E. DeBoer

Abstract

Several surface water treatment plants obtain their source water from the four reservoirs behind the dams on the Missouri River in South Dakota. These treatment plants must treat their water to meet the requirements of the Disinfectants/Disinfection Byproducts (D/DBP) Rule. The D/DBP Rules require coagulation and/or softening plants to achieve total organic carbon (TOC) removal percentages that vary with the source water quality. Organic carbon compounds (measured as TOC concentration) are precursors to disinfection byproducts (DBPs). Maximum contaminant levels (MCLs) for the organic DBPs, including total trihalomethanes (TTHMs) and haloacetic acids (HAAs) of samples collected in the distribution system, are also mandated by the D/DBP Rule. This study examines the impacts of TOC removal and disinfection modifications by Missouri River water treatment facilities on DBPs in the water provided to their distribution systems. Historical data related to water quality changes in the Missouri River reservoir system were interpreted and changes in source water quality due to treatment process operations and TOC removal efficiency were evaluated. Additional factors to the formation of DBPs such as TOC concentration, pH, chlorination time and temperature were considered. The impact of disinfection technologies on DBP production at varying levels of enhanced coagulation was examined and an analysis of jar testing was performed in accordance to the Stage 2 Enhanced Coagulation Jar Test Protocol. Simulated Distribution System (SDS) tests were also conducted to relate TOC removal to DBP formation. Results of this study concluded that the Missouri River water quality is affected by the hydraulics and hydrology of the reservoir operations. The TOC concentrations of the four reservoirs have increased to greater than 4.0 mg/L as Lake Oahe filled during the latter part of the 2000-2010 decade. As indicated by recent raw and treated water quality data and results from enhanced coagulation jar tests, coagulation facilities treating Missouri River water have difficulty meeting the enhanced coagulation requirements of the D/DBP Rule, whereas softening facilities routinely met the enhanced coagulation requirements. Furthermore, enhanced coagulation jar test results verified that the Missouri River reservoir water may not be amenable to enhanced coagulation. Due to the reactive nature of the treated water TOC, most coagulation systems have implemented chloramination to establish a secondary disinfectant that controls DBP formation in their distribution systems. SDS tests conducted in this thesis validated the benefits of chloramination as a DBP compliance technique. Conclusions from this study were used to provide an educational workshop attended by Missouri River water system employees and other interested parties.

Library of Congress Subject Headings

Water -- Purification -- Disinfection -- Missouri River -- By-products
Water treatment plants -- Missouri River

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Rights Statement

In Copyright