Sharon Walker, L

Sharon  Walker
Assistant Professor;
John Babbage Chair in Environmental Engineering

Mailing Address:

Chemical and Environmental Engineering
Bourns Hall /B355
University of California
Riverside, CA 92521

Phone: (951) 827-6094
Fax: (951) 827-5696


PhD 2004 Yale University
MS 2000 Yale University
BS 1998 University of Southern California

College/Division Affiliation:

Bourns College of Engineering

Center/Inst Affiliation(s):

Center for Plant Cell Biology

Areas Of Expertise:

Bacterial Adhesion and Transport in Natural and Engineered Systems; Water Quality Engineering

Research Summary:

My overall research goal is to establish the mechanisms contributing to pathogen interactions with surfaces.  Ultimately these mechanisms will influence the fate and transport of these pathogens in aquatic environments.  Particular emphasis is placed on groundwater systems; however, vadose zone and surface water systems are also studied.  This work is imperative for properly assessing the environmental impact of groundwater contamination from sources including urban runoff, septic tank/leach field systems, and animal manure from agricultural operations.  The information is also vital for effective design of water quality technologies including riverbank filtration, wastewater reclamation, and recharge into aquifers.  Additionally, with this crucial knowledge, design of surface coatings and processing can be optimized for minimal biofouling in marine environments. The specific areas of research currently being conducted are as follows:

Area 1. Role of chemical and physical heterogeneity on bacterial cell adhesion.  This research effort focuses on the interactions occurring between a model particle (bacterium as well as a polystyrene colloid) and collector surfaces in simulated seawater or groundwater environments.  Both the physical and chemical heterogeneous nature of the particle and collector surfaces is systematically modified and the extent to which altering this influences adhesion is quantified within a packed-bed column, a parallel plate (PP) flow cell, and the radial stagnation point flow (RSPF) system.  Collector surface modification is done utilizing a sintering technique or by zeolite coating, which allows for nanometer scale control of both chemical and physical surface features.  The intent of this work is to establish the role of heterogeneity on the adhesion of bacteria which lead to biofilm development.  (Collaborators: Prof. Yushan Yan, Chemical and Environmental Engineering Dept., UCR; Assistant Prof. Javier Garay, Mechanical Engineering Dept., UCR)


Schematic of Parallel Plate System


Area 2.  Influence of extracellular polymeric substances (EPS) on cell adhesion and transport. This project is examining the extent to which transport of pathogens in porous media is controlled via cell surface polymers. Specifically, the impact of bacterial metabolic and environmental conditions on EPS production and composition (relative amounts of protein, polysaccharide, and nucleic acid content) and subsequent influence on adhesion is being assessed using packed bed column experiments.   Parameters such as pore water content, temperature, solution chemistry, and bacterial cell condition are systematically varied to simulate subsurface conditions.  Additionally, the influence of these parameters on the genotype of the cell is being investigated, and ultimately the effect on pathogen virulence can be assessed.  (Collaborator: Professor Heather Smith, Riverside Community College; Funding: National Water Research Institute, UC Center for Water Resources, USDA CSREES HSI)

Area 3. Coupled role of physical and chemical interactions in pathogen transport in porous media.  This research effort combines experimental and theoretical methodologies at several spatial scales. Extended DLVO theory calculations and direct measurement of pathogen-pathogen interaction forces using atomic force microscopy (AFM) are being utilized to determine colloid-colloid and colloid-collector grain interaction energies. Packed bed column experiments and real time direct observation of pore-scale deposition processes using the RSPF are being conducted to determine the dominant deposition mechanisms.   In addition to current colloid studies, a model E. coli and Cryptosporidium will be utilized in the future.  (Collaborators: Prof. Bill Johnson at the University of Utah and Dr. Scott Bradford at the USDA-ARS Salinity Laboratory; Funding: USDA CSREES NRI)


Schematic of experimental systems in use for Area 3

Selected Publications:

List of publications from HubMed


Lab Personnel: +

Torkzoban, Saeed
Postdoctoral Researcher —
Chen, Gexin
Graduate Student — Bacterial Cell Adhesion
Gong, Amy
Graduate Student — Bacterial surface polymer composition
Haznedaroglu, Berat
Graduate Student — Pathogenic characteristics of Salmonella spp., and Rotavirus in groundwater environments
ShojaeTazehkand, Shiva
Visiting Graduate Student —
Borneman, Breanne
Undergraduate —
Salam, Christopher
Undergraduate —