Date of Award

Spring 1-1-2010

Document Type

Thesis

Degree Name

Master of Science (MS)

First Advisor

Angela R. Bielefeldt

Second Advisor

R. Scott Summers

Third Advisor

Joseph N. Ryan

Abstract

Ceramic water filters are used in many developing countries as a household water treatment technology, often produced locally using regionally-available materials, and constructed in various forms (i.e., as discs, candles, or pots) that all rely on similar mechanisms of filtration and inactivation. A common production technique involves application of an anti-microbial, colloidal silver coating to the porous ceramic filter. The silver coating has shown improvements in microbial log reduction values over uncoated ceramic filters both in the laboratory and in the field. However, a more complete understanding of the silver coating requires knowledge of specific characteristics of the colloidal silver solution, including particle size, composition, and charge, and to understand how these characteristics affect silver particle deposition, anti-microbial activity, and potential optimization of the silver coating. Additionally, as water passes through the ceramic filter, the silver coating will release from the ceramic surface, decreasing the effectiveness of the filter by reducing the presence of silver.

A colloidal silver solution was prepared according to procedures recommended for ceramic pot filter production. The solution was then characterized for particle size distribution, trace contaminants, and zeta potential. Silver nanoparticles were adsorbed onto a silica substrate and assessed with a quartz crystal microbalance. Preliminary experiments showed adsorbed silver releasing from an unmodified quartz sensor (gold electrode surface) into flowing 10% (v/v) influent solution of tryptic soy broth at approximately 50 times the rate of release of adsorbed silver caused by flowing Millipore ultrapure water alone. Experiments were conducted to determine the effects of water quality, including pH, turbidity, ionic strength, and natural organic matter, on the release of silver nanoparticles from the silica substrate. The most significant release was caused by waters containing sodium hypochlorite, suggesting that cleaning of silver-containing ceramic filters should be performed with caution.

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