Date of Graduation

12-2013

Document Type

Thesis

Degree Name

Master of Science in Environmental Engineering (MSEnE)

Degree Level

Graduate

Department

Civil Engineering

Advisor

Julian Fairey

Committee Member

Wen Zhang

Second Committee Member

Ashley Pifer

Keywords

Applied sciences; Chlorination; Disinfection byproducts; Water treatment

Abstract

A disinfection byproduct (DBP) formation potential (FP) test can be used to indirectly measure the concentration of DBP precursors in natural waters, permitting assessment of various DBP-related treatment processes and control strategies. While these tests require a 7-day chlorine residual (CR) between 3-5 mg L-1 as Cl2, it is not well known if this recommended residual corresponds to the true DBPFP (i.e., the maximum concentrations) for trihalomethanes (THMs) and haloacetonitriles (HANs). In this study, THMs and HANs were quantified as a function of CR under three common disinfection regimes: (1) free chlorine at pH 7.0 (FC7), (2) monochloramine at pH 7.0 (MC7), and (3) monochloramine at pH 8.3 (MC8). Three source waters were collected, one from a drinking water source (LW) and two from the effluent of a wastewater treatment plant (WW1 and WW2), and used to generate a total of 90 sample waters for the DBPFP experiments. Trichloromethane (TCM) was the predominant THM formed in the sample waters, and, for MC8, achieved its maximum value of ~40 µg L-1 at a CR of 30 mg L-1 as Cl2 (referred to as CRMAX), and in excess of the 3-5 mg L-1 as Cl2 target residual. For the FC7 and MC7 disinfection regimes, TCM concentrations continued to increase beyond the maximum CR achieved in this study (73.6- and 17.1 mg L-1 as Cl2, respectively), indicating its true FP was not reached. CRMAX values for the bromine-substituted THMs and HANs varied by disinfectant type and pH, however none were between the 3-5 mg L-1 as Cl2 recommended residual, and were limited by the low bromide concentrations in the source waters (< 0.24 mg L-1). For dichloroacetonitrile, the predominant HAN formed, the CRMAX was 1.5-1.7 mg L-1 as Cl2 for FC7 and in excess of 15 mg L-1 as Cl2 for MC7 and MC8. The results of this study demonstrate the impact of CR on the formation of THMs and HANs, and can be leveraged to help assess various DBP-precursor removal processes and be used to guide development of more a more robust DBPFP test.

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