There is no data currently on the possible effects of biofilm in drinking water storage tanks on the water's microbial quality aboard commercial aircraft.
Dr. Butterfield has recently begun a research project to help answer questions regarding aircraft tank biofilm and the effectiveness of current disinfection protocols in the control of biofilm. The project will include investigating the survival of a pathogen that might accidentally contaminate the water storage tanks.
Since aircraft tanks are lined with materials not commonly found in municipal drinking water systems (ABS and PETG plastics), the project will investigate biofilm formation on those materials under conditions similar to those found in an aircraft storage tank.
CDC biofilm reactors (BioSurface Technologies) are being used to simulate the tank environment. Using a programmable controller, the reactor contents are replaced with fresh tap water by controlling valves, feed pumps and reactor mixers. One reactor receives water amended with calcium to increase the water's hardness, another is amended with carbon compounds to increase the biodegradable carbon in the water, and another reactor receives un-amended tap water. The reactors are operated for two months before being sampling for biofilm and assessing the effectiveness of a disinfection regimen.
While associated with the Center for Biofilm Engineering Dr. Butterfield started to investigate the use of a granular media, packed biofilm column as a device to trap and assist in detection of pathogens or potential bioterrorist agents in drinking water.
His work has demonstrated that the biofilm was capable of capturing and retaining a slug-dose of Escherichia coli O157:H7.
In addition to effective capture of the pathogen, Dr. Butterfield developed techniques to efficiently sample biofilm from the entire depth of the media without physical removal of the media. He continued this research at the University of Washington using a variety of granular media and contaminant doses.
Bench-scale granular-media, packed biofilm columns. Left column: plastic media - Right column: porous glass media
Macrolite® media in a small, upflow biofilm column.
Novel Methods to Concentrate Pathogens in Water
One technique being used to concentrate pathogens in water is using hollow fiber ultrafiltration membranes. Since pathogens will not pass through the membrane, a large volume of water can be filtered and the pathogens concentrated into a much smaller volume, making pathogen detection easier to perform.
Hollow-fiber ultrafiltration membrane unit used to concentrate large sample volumes.
The goal of the project Long-term Microbial Safety of UV Light Disinfection Point-of-Entry Water Treatment Devices was to determine if pathogens could survive in a simulated home plumbing system following UV light disinfectionby by a typical point-of-entry device. Many pathogens and viruses are capable of attachment to drinking water biofilm and persisting for some time; some are known to have the potential for repair of damage created by the UV light.
Pathogens that may not have been totally inactivated by the UV
light could become part of the biofilm where they can undergo
possible repair, growth, or simple persistence. Any release of the
pathogen from the biofilm back into the water would allow entry to
the home water system and potential ingestion.
Conclusions of the Study
POE UV light disinfection units of the type examined in this study can provide a high level of disinfection and are most suitable for better quality water supplies, such as ground water, that have a low potential for fecal contamination. Inactivation of viruses could be an issue for these treatment systems if viral contamination occurs in concentrations greater than ~105 per liter. In those instances where a high concentration of virus is possible the UV-treated water could contain a sufficient level of virus particles to cause illness.
The viral indicator MS2 showed only weak persistence over the seven day sampling period, and no culturable MS2 were detected in the 3 and 7 day samples. The inability of MS2 to persist would indicate there is less risk of long-term contamination, even though others have found long-term persistence in distribution system models.
Culturable S. typhimurium were detected initially and at 3 and 7 days after inoculation, supporting the possibility for this pathogen to survive UV disinfection and persist in the system. UV light inactivation did not prevent capture of E. coli O157:H7 and S. typhimurium by biofilm. Although the biofilm samples were consistently negative for culturable bacterial pathogens, it was demonstrated that if any bacterial pathogens were not inactivated the potential exists for capture, persistence, and possible later contamination water as part of detached biofilm. Residual chlorination using free chlorine at very low doses would reduce the risk of long-term contamination in a system using POE UV disinfection.
Water reuse involves taking water of a lower quality, such as the treated effluent from a municipal wastewater treatment plant, treating the water to attain higher quality, and then using the water for a beneficial use such as irrigation or recharge of groundwater aquifers. Maintaining the microbial quality of reuse water within storage tanks and distribution pipelines is important to assure there is minimal risk to the end user with regard to waterborne disease. Biofilm on the walls of pipes and tanks can play an important role in determining the quality of the delivered reuse water.
In a first-of-its-kind study, actual water reuse distribution systems were investigated to determine changes in the quality of reuse water as it moved through the distribution system, the effects of biofilm in modifying the microbial quality of the reuse water, and operational characteristics that lead to improved reuse water quality. Pipe loops and rotating annular reactors were distributed throughout the reuse distribution systems and sampled for biofilm to determine the amount of biofilm present, basic composition of the biofilm, and if pathogen indicator organisms were present in the biofilm.
With respect to biofilm in the distribution systems there were two significant findings. The first had to do with the composition of the biofilm. The graph below presents monthly data for one point in a reuse system. Heterotrophic plate counts (HPCs) provide a general indication of the total amount of biofilm present on the pipe walls. Total coliforms made up an average of 47% of the total biofilm based on HPCs. E. coli were detected frequently, but not in great numbers. These results show that even though the reuse water was disinfected to a high degree and a chlorine residual was present in the reuse water, the biofilm in the pipe had numerous organisms that, if released back into the reuse water through sloughing of the biofilm, could lead to microbial degradation of the reuse water.
The second significant finding was that PVC pipe had less biofilm than did ductile iron (DI) pipe lined with cement mortar lining. This finding has also been found in drinking water distribution systems.
Toolbox to Assess Potential Microbial Contamination Risks in Small Water Systems
Small water systems have been the site of many waterborne disease outbreaks. The Walkerton, Ontario, Canada, E. coli O157:H7 waterborne outbreak was one example of the problems small water systems now face in providing safe drinking water.
Dr. Butterfield developed a toolbox (assessment methodology) that will allow small water systems to assess each component of their system to determine where their greatest potential microbial contamination risks are located.
The questionnaire and computer spreadsheet application have been combined with an interactive training tool and are available from the Montana Water Center's Technical Assistance Center.
Example chart from Ranking Tool showing relative potential risk scores for two water sources.
In May 2004, an international colloquium was held at Montana State University to explore, enhance and document the science that informs decision-making on the health risks associated with small water systems. Specific objectives were:
1) systematically explore those risks with water scientists, engineers, system managers and operators, risk assessors and regulatory authorities;
2) facilitate a full exchange of experiences and "lessons learned" among these experts regarding the protection of the public in small water systems in their nations; and
3) prepare a report to be used for education/outreach purposes, as a tool for policy makers, and to assist in focusing current and new research monies toward the development of novel solutions.