Date of Award

August 2013

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Engineering

First Advisor

Jin Li

Committee Members

Ching-Hong Yang, Shangping Xu, Hector Bravo, Qian Liao

Keywords

Biofilm, E.Coli O157:H7, Graphene Oxide, Lipopolysaccharide, Phosphate, Transport

Abstract

Groundwater is an important source for drinking water supply. Microbial contaminants have been implicated in two-third of the waterborne disease outbreak. Understanding the fundamental processes, the governing factors and the interfacial interactions that contribute to the deposition of microbial contaminants to porous media will help to elucidate the microbial attachment/transport profile and is highly needed for bioremediation in the environment as well as water purification industry.

In this study, the effects of (1) chemical factors including ionic strength, pH and concentration of phosphate, (2) biological factors including lipopolysaccharide (LPS), biofilm and biofilm extracellular polysaccharide (EPS), and strain type on E.coli O157:H7's transport and deposition in saturated sand columns were investigated. The contributions of surface charge, hydrophobicity and steric force to bacterial attachment were quantitatively assessed by calculating extend DLVO theory and steric interaction. Moreover, the role of LPS in protecting bacteria from antibacterial effect of graphene oxide(GO) was studied. At last, the role of surface functional groups in antibacterial activities of carbon nanotubes was examined.

The overall findings in our study are as follows: (1) The transport of E.coli O157:H7 through saturated porous media is enhanced with increasing ionic strength and pH condition; (2) The presence of phosphate in water body encourages the transport of E.coli O157:H7 cells through porous media; (3) LPS on the cell surface facilitate E.coli O157:H7's transport in sand columns; (4) The retention of E.coli O157:H7 in sand is significantly lower than E.coli JM109 under various solution chemical conditions; (5) The association of E.coli bacteria with biofilm coated on the porous media substantially increase the attachment of cells; (6) XDLVO integrating with steric interaction can qualitatively explain our observations about the retention of E.coli O157:H7 on sand surface; (7) The LPS component can protect E.coli O157:H7 cells from antibacterial activities of GO sheets; (8) Carbon nanotubes functionalized with amine groups have the highest bacterial removal efficiency. The adsorption of bacteria to the nanomaterials fits to Langmuir isotherm equation and can be expressed by pseudo second order kinetics equation.

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