Date of Graduation

12-2011

Document Type

Thesis

Degree Name

Master of Science in Civil Engineering (MSCE)

Degree Level

Graduate

Department

Civil Engineering

Advisor/Mentor

Julian L. Fairey

Committee Member

James C. Young

Second Committee Member

Wen Zhang

Keywords

Applied sciences, Disinfection by-products, Dissolved organic matter, Fluorescence, Ion exchange, Parallel factor analysis

Abstract

Disinfection by-products (DBPs) form as an unintended result of drinking water disinfection, from chemical reactions between disinfectants (e.g., free chlorine) and naturally occurring dissolved organic matter (DOM). At present, 11 DBPs are regulated in treated drinking waters due to potential adverse health effects, including four trihalomethanes (THMs). Despite nearly 40 years of DBP research, compliance with DBP regulations remains a challenge for many drinking water treatment plants (DWTPs), including the four DWTPs located on the Beaver Lake Reservoir in Northwest Arkansas. Due to the high net negative surface charge on DOM, anion exchange is one potentially viable method for removing DOM from drinking water sources. Here, magnetic ion exchange, or MIEX®, was evaluated for removal of DBP precursors. Raw water samples were collected monthly between April-August, 2011 from four DWTPs on Beaver Lake. The waters were adjusted to pH values of 6, 7, and 8 and treated with fresh MIEX® resin at a dose of 6 mL/L. After treatment, the samples were dosed with free chlorine and the DBP formation potential (DBPFP) was measured. Three DBPs - chloroform (TCM), dichlorobromomethane (DCBM), and dichloroacetonitrile - formed at measurable concentrations which varied by sample location and date, indicating spatial and temporal variability in the DOM throughout the study period. TCM was the predominant DBP formed and was removed to the greatest extent (75-82%) by MIEX® treatment, with no apparent trends with source water pH. In an attempt to related DOM properties to DBPFP, fluorescence excitation-emission matrices (EEMs) were collected for 200 raw and MIEX® treated water samples. A statistical algorithm, parallel factor (PARAFAC) analysis, was used to decompose the EEMs into four principal component fluorophore (three humic-like and one protein-like) groups, each with a maximum intensity, FMAX value. FMAX values of two of the humic-like fluorophore groups more were strongly correlated with TCM formation potential (r2 values of 0.81 and and 0.74) than specific ultraviolet absorbance at 254 nm (SUVA254, with an r2 of 0.01). These results highlight for the first time the usefulness of fluorescence-PARAFAC to assess DBP formation and control using MIEX® treatment and may be extended to optimize treatment conditions for DBP-precursor removal by ion exchange.

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