Semester

Summer

Date of Graduation

2012

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Civil and Environmental Engineering

Committee Chair

Lian-Shin Lin

Abstract

The occurrence of emerging or newly identified contaminants in our water resources is of rising concern for human health and the environment. Nanomaterials rise to be among the major emerging contaminants in recent years because of their broad applications. The existing conventional water and wastewater treatment plants are not designed for removal of these contaminants. To date, little is known about the fate and impacts of these contaminants in the water systems.;Engineered nanomaterials such as titanium dioxide (TiO2) are known to produce reactive oxygen species (ROS) under irradiation of ultraviolet or visible light. A sub-lethal level of ROS could trigger microbial defense mechanisms which protect microorganisms from environmental oxidative stress and its damages. This microbial resistance to environmental oxidative stress may increase the threat to human health. Conversely, excessive amounts of ROS have a cytotoxic effect on microorganisms by causing membrane and DNA damages. The damages can reduce microbial viability, making the microorganisms more susceptible to other oxidants such as chemical disinfectants used for wastewater disinfection. As a result, the interactions of nanomaterials with microorganisms are expected to affect the efficiency of chemical disinfection. Understanding the potential of ROS generation for nanomaterials and its relationship with bacterial inactivation is important to track the impact of nanomaterials in the water purification systems. In this thesis, the relationships between reactive oxygen species production rates and Escherichia coli inactivation rates of five engineered titanium-oxide nanomaterials with a range of shapes, sizes, crystal structures, and chemical composition were studied. Hydroxyl radical (·OH) and superoxide ion (O2 .-) production rates of the nanomaterials under long-UV irradiation were estimated using species-selective probe molecules and spectrophotometric measurements. The bacterial inactivation rates were estimated by a series-event kinetic model and were compared across the five materials on a per unit surface area basis. Photo-energy utilization efficiency of these nanomaterials for ROS production varied with not only with the type of materials but also with irradiation intensity and nanomaterial loading. Degussa P25 was found to have a distinctly different correlation between ·OH production rate and bacterial inactivation rate from that of the remaining nanomaterials. The results support the use of a metric of multiple ROS or biological responses for more accurately characterizing and predicting disinfection efficiency or other cytotoxic effects of metal-oxide nanomaterials across a range of physicochemical properties.

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