Grantee Research Project Results
2013 Progress Report: Association of Pathogens with Biofilms in Drinking Water Distribution Systems
EPA Grant Number: R834870Title: Association of Pathogens with Biofilms in Drinking Water Distribution Systems
Investigators: Nguyen, Thanh (Helen) H. , Hozalski, Raymond , Liu, Wen-Tso
Institution: University of Illinois Urbana-Champaign , University of Minnesota
EPA Project Officer: Packard, Benjamin H
Project Period: June 1, 2011 through May 28, 2016
Project Period Covered by this Report: June 1, 2013 through May 28,2014
Project Amount: $600,000
RFA: Advancing Public Health Protection through Water Infrastructure Sustainability (2009) RFA Text | Recipients Lists
Research Category: Drinking Water , Water
Objective:
- To address the public health risk due to waterborne pathogen contamination of the distribution system.
- To identify the factors that influence the persistence of a model pathogen, Legionella, in multi-species biofilms grown on different pipe materials under conditions relevant to distribution systems.
- To use molecular biology and surface chemistry tools to characterize the microbial communities and the surface properties of the biofilms, respectively.
- To further investigate novel chemical and enzymatic treatments to weaken the biofilm to promote detachment and improved cleaning.
Progress Summary:
- We identified the effect of monochloramine exposure on biofilm physical structure and adhesion kinetics of an environmental Escherichia coli strain and a pathogenic L. pneumophila strain. Biofilms were grown with groundwater on PVC coupons in CDC reactors for 8 weeks prior to disinfection treatments for 12 weeks. The biofilm structure, such as biofilm thickness and roughness was determined with optical coherence tomography (OCT) and confocal laser scanning microscope (CLSM). The OCT results revealed that 12-week exposure to monochloramine led to smoother biofilm surface and the treatment did not eliminate the biofilm. Adhesion for E. coli and L. pneumophila was lower on the smoother treated biofilm surface compared to on rougher untreated biofilm surface.
- We used computational fluid dynamics (CFD) and particle tracing simulation to show that enlarged biofilm surface area and significantly changed direction of flow streamline along the rough biofilm asperities and the low flow zones surrounding the roughness asperities enhanced particle adhesion on rough surface.
- Higher flow rate was found to facilitate L. pneumophila detachment from a given biofilm, due to the higher shear stress revealed by CFD simulation. For 15 and 40 mL/min flow rates, detachment from the rough biofilm was lower compared to the smooth biofilm because larger low-shear-stress zones were created on the rough surface. At the flow rate of 100 mL/min, equally high detachment was found for both smooth and rough surfaces in agreement with the simulated shear stress profiles. This study identified that the biofilm physical structure and the local hydrodynamics are the key factors controlling L. pneumophila attachment and detachment.
- Pipe material was a much less significant factor in the accumulation of biofilm than the chlorine level. Approaches that worked well for weakening and removal of single species Staphyloccocus epidermidis biofilms (e.g., chelators) were not effective at removing undefined mixed community biofilms.
Future Activities:
- Biofilms will be grown from groundwater for 8 weeks and then exposed to monochloramine for up to 12 weeks. Biofilm samples will be characterized with respect to structure and cohesiveness, and the characteristics will be used to explain the detachment data of L. pneumophila.
- Adhesion of L. pneumophila cells under different environmental stress to copper coupons at different temperatures will be quantified. Mechanisms of adhesion will be determined.
- Long-term adhesion and detachment of L. pneumophila in a pipe system will be studied.
- Due to the long time required to grow biofilm that is relevant for a drinking water distribution system, we would like to request a 1-year no-cost extension. In addition, because of the departure of our EPA collaborator, Dr. Nicholas Ashbolt from EPA, we would like to have a different collaborator, Dr. Jorge Santo Domingo.
Journal Articles:
No journal articles submitted with this report: View all 8 publications for this projectSupplemental Keywords:
drinking water, pathogen, biofilms, drinking water distribution systemProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.