Date of Award

2013

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil Engineering

First Advisor

Vinka Oyandel-Craver

Abstract

Nanotechnology is an emerging and fast-growing technology. Currently, there are more than 1,317 nanotechnology-based products on the market. Silver nanoparticles account for more than 23% of all nano-products. The extensive application of the silver nanoparticle (AgNP) results in their inevitable release into the environment. Silver nanoparticles are known as excellent antimicrobial agents, and therefore they could be used as alternative disinfectant agents. On the other hand, released silver nanoparticles could pose a threat to naturally occurring microorganisms.

In Chapter 1, we introduce the background information on the environmental fate, toxicological effects, and application of AgNP and review the current knowledge on the physicochemical and antimicrobial properties of AgNP in different aqueous solutions, as well as their application as alternative disinfectants in water-treatment systems.

In Chapter 2 of this dissertation, we discuss the evaluation of AgNP’s antimicrobial properties at different water chemistry conditions. It was found that the aggregation of silver nanoparticles depends on the properties of the background ions, such as Na+ and Ca2+, at different water chemistry conditions. Divalent cations can significantly enhance the aggregation, while monovalent cations and anions do not have such a significant influence. A saturation-type fitting curve was established, showing the survival of bacteria under different water chemistry conditions as a function of the size of the nanoparticles.

In Chapter 3, we talk about the evaluation of the antimicrobial properties of AgNP when coated with different organic compounds using natural water conditions. The results obtained showed that silver nanoparticles in surface water, ground water, and brackish water are stable. However, in seawater conditions, AgNP tend to aggregate. This study also shows that the antimicrobial activity of AgNP can be impaired by the presence of a humic substance and high concentrations of divalent cations. These results are helpful in explaining how discharged AgNP behave in natural aquatic systems as well as their environmental toxicological effects on naturally occurring microorganisms.

In Chapter 4, we discuss the investigation of the effect of silver nanoparticles on a model virus-MS2 bacteriophage. A negligible deactivation effect on MS2 phage was found regardless of the type of AgNP and the water chemistry conditions used.

In Chapter 5, we talk about the comparison of AgNP-impregnated point-of-use ceramic water filters and ceramic filters impregnated with silver nitrate. This study was performed using different water chemistry conditions and different manufacturing materials. The results showed that AgNP-impregnated ceramic water filters are more appropriate for this application due to the lesser amount of silver desorbed compared with silver nitrate-treated filters. The bacterial removal performance of the silver-treated ceramic filters and concentration of viable bacteria in the filters are dose-dependent on the amount of silver applied. However, the data showed that influent water chemistry conditions did not have a significant effect on the performance of the filters. This study established evidence-based silver application guidelines for the ceramic water filter manufacturers around the world.

In Chapter 6, the discussion centers in the comparison of a polymer-based quaternary amine functionalized silsesquioxanes compound and AgNP. The results showed that the quaternary ammonium functionalized silsesquioxanes-treated ceramic water filter desorbed less from the filters and achieved higher bacteria removal than the filters impregnated with AgNP. This indicates that the quaternary ammonium functionalized silsesquioxanes compound could be considered as a substitute for silver nanoparticles due to its lower price and higher performance. However, more information regarding the possible chronic health effects of the silsesquioxanes compound is needed.

In Chapter 7, we present the main conclusions and recommended future work based on the dissertation results.

Share

COinS