Date of Award

May 2015

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Engineering

First Advisor

Zhen He

Second Advisor

Ying Li

Committee Members

Hector Bravo, Jin Li, Yin Wang, Ernie Lee

Keywords

Disinfection, Drinking Water, Photocatalysis, Water Softening

Abstract

Trends in drinking water treatment in recent years have been moving toward the use of membrane separation in order to reduce contaminants in water. There are many forms of membrane separation technology such as ultrafiltration, nanofiltration, microfiltration, reverse osmosis, and extruded ion exchange membranes. These membranes have many different applications and may be used to remove many materials from water such as salts, viruses and bacteria, selectively remove cations or anions, or remove organics.

Microbial desalination cells (MDCs) are an emerging concept which use bioelectric potential produced from organics via microbial metabolism to accomplish desalination. MDCs consist of three compartments, the anode, the cathode, and a salt compartment, which is between the anode membrane and the cathode membrane. This study reported a bench-scale laboratory experiment for evaluating the effectiveness of using MDC technology to remove hardness from several different hard water samples collected from across the United States, ranging in concentrations from 220 to 2080 mg/L as CaCO3. It was found that the MDC generally removed more than 90% of the hardness from the tested water samples driven by electron movement in batch operation. Electricity production was highly related to the conductivity of the hard water samples. It was also found that the MDC could remove 89% of arsenic, 97% of copper, 99% of mercury, and 95% of nickel at the testing concentration in a synthetic solution. These results provided a proof-of-concept that MDCs can be used to soften hard water that is driven by an electric current.

Photocatalysis is an attractive technology for the disinfection of microorganisms in drinking water. Titanium dioxide (TiO2) is widely recognized for its disinfecting capabilities under the irradiation of ultraviolet (UV) light. Metal ions such as silver and copper serve as good dopants for TiO2 in order to increase the photoactive yield and are also known for their bactericidal properties. This report details a method for the combination of silver and copper ions onto TiO2 and the evaluation of its disinfection efficiency. TiO2, Ag-TiO2, Cu-TiO2, and Ag-Cu-TiO2 were applied onto a glass-fiber membrane substrate and irradiated with a UV light taken from an existing point-of-use UV disinfection filter. When activated with UV light, the Ag-Cu-TiO2 membranes exhibited stronger bactericidal and virucidal activity than UV alone, TiO2, Ag-TiO2, or Cu-TiO2. For experiments conducted in the dark, bactericidal activity of the Ag-Cu-TiO2 membranes was greater than that of Ag-TiO2 or Cu-TiO2 suggesting that the silver and copper worked in a synergistic antibacterial effect unrelated to photoactivity. These results have shown that a silver-copper doped titanium dioxide membrane can be effective for removing bacteria and viruses from drinking water.

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