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Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Civil Engineering

Year Degree Awarded

Spring 2014

First Advisor

David A. Reckhow

Subject Categories

Civil and Environmental Engineering

Abstract

Drinking water disinfection byproducts (DBP) are a group of inorganic and organic compounds formed during water disinfection. Epidemiologic studies suggest an association between rectal, and colon cancer and exposure to DBPs in chlorinated surface water. Therefore, DBPs are a growing public health concern; one that has been mitigated by multiple regulations of US Environmental Protection Agency (EPA) including the Stage 2 Disinfectants and Disinfection Byproducts Rule (Stage 2 DBPR). Tremendous efforts and cost have been spent on controlling DBPs in drinking water; however, human exposure has been poorly characterized. In addition to ingestion exposure, inhalation and dermal absorption during showering for example could also be significant exposure pathways. This dissertation focuses on investigating DBP formation and degradation in heated water (~50oC) in both lab simulated tests and field studies.

The first objective of this dissertation was to investigate the temporal variability of regulated DBPs and non-regulated DBPs in cold and hot tap water at a residential home, in a water plant and in a simulated distribution system test. The results showed that the residence time of water in hot water tanks plays an important role on the formation and degradation of DBPs in the hot water plumbing. There was no obvious difference between the concentrations of TCAA (trichloroacetic acid) in long-heated hot tap water and cold tap water. The terminal DBPs for cold and hot tap water were measured and compared to the instantaneous DBP formation in cold and hot tap water. The heating of tap water in the water tank was found to increase the extent of THM formation.

The second objective of this dissertation was to investigate the impact of heating scenarios on the formation and degradation of DBPs. A field study involving homes equipped with either tankless heaters or tank heaters was conducted. The concentrations of DBPs were measured for cold and hot tap water of each home. A lab-controlled heating test was later on set up to investigate the formation and degradation of DBPs in short term and long term heating to understand the difference in DBP concentrations in the hot tap water out of different types of water heaters. The results from the field study revealed that the differences in DBP levels in the hot tap water out of the two types of heaters were statistically significant for chlorine residual, total trihalomethanes (TTHMs), dichloroacetic acids (DCAA), dichloroacetonitrile (DCAN), trichloroproprane (TCP) and chloropicrin (CP). Bench scale heating tests showed that long term heating changed the concentrations of DBPs significantly.

The third objective of this dissertation was to investigate the thermal formation and degradation in various conditions. Especially, the impact of water age on DBP formation and degradation in cold and heated water was investigated. The results of this study demonstrate that DBP concentration profiles in heated water were quite different from the DBP concentrations in the cold tap water. Chloroform concentrations in the heated water remained constant or even decreased slightly with increasing distribution system water age, despite the fact that its levels always increased with water age in the cold water.

The final objective of this dissertation was to propose a method to model chlorine decay, not only in the distribution system, but also applicable to home heating scenarios. A robust two-site chlorine decay model of combined effects of pH, temperature in water distribution system and heating condition was proposed. A single set of readily interpretable parameters were estimated by stochastic search using differential evolution.

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