Final Report: Sustainability of the Filtrón for Microbial Disinfection

EPA Grant Number: SU832500
Title: Sustainability of the Filtrón for Microbial Disinfection
Investigators: Summers, R. Scott , Bielefeldt, Angela , Shah, Jay , Cornejo-Warner, Pablo
Institution: University of Colorado at Boulder
EPA Project Officer: Nolt-Helms, Cynthia
Phase: I
Project Period: September 1, 2005 through August 31, 2006
Project Amount: $9,992
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2005) RFA Text |  Recipients Lists
Research Category: P3 Challenge Area - Built Environment , Pollution Prevention/Sustainable Development , P3 Awards , Sustainability


A significant portion, ~20%, of the world’s population lives without access to safe water. Point of use (POU) devices for disinfection have been under-utilized as a tool to provide access to safe water. One such effective POU for producing potable water is the Filtrón; a ceramic filter coated with colloidal silver, which is manufactured locally in several developing countries, first started by Potters for Peace in Nicaragua. The production of the filters is a locally sustainable micro-enterprise and provides an income source. While filter production requires some technical expertise and implementation requires some education, they are relatively inexpensive and do not require massive infrastructure, which is essential in that they are implemented in communities that survive on little to no monetary income. While the Filtrón performance has been successfully demonstrated in the lab and in the field, its long-term performance and sustainability has not been critically evaluated, which is the objective of this study.

The effectiveness of the Filtrón is attributed to the micro-pores in the ceramic that are sized small enough to exclude microbial pathogen passage and by the colloidal silver coating which can inactivate microorganisms, as well as prevent their regrowth in the filter. The long-term effectiveness of both mechanisms will be evaluated. The first task is to evaluate the performance of filters that have been in use for several years relative to the bacterial effectiveness of new filters. We have initially utilized new filters and filters that have been in use for a number of years in Nicaragua for long term effectiveness study. Once the performance of these filters has been established, we will evaluate methods of regenerating the filters with diminished capacity. These methods include physical cleaning and reapplication of the colloidal silver. Our next task is the evaluation of the microbial regrowth in the used and new filters. Our last task is the evaluation of the initial silver concentration on the microbial effectiveness. Different amounts of colloidal silver will be coated onto new filters and the impact on microbial effectiveness evaluated.

Summary/Accomplishments (Outputs/Outcomes):

The filters tested in each trial had initial filtration rates in the 1-2 L/hour range, consistent with recommendations for efficient flowrate. All control trials showed no growth of bacteria on the plates prior to microbial solution addition. All trials exhibited a significant reduction in bacteria concentration after filtering.

From our results, it is evident that the new filter exhibits over a 3-log reduction in microbial concentration at both 2- and 4-hour intervals of sampling during filtration. The old filter, approximately 4 years household use time in Nicaragua, has close to a 2-log reduction in microbial concentration. While this indicates a difference in microbial effectiveness between the used and new filters, the used Filtrón still exhibits a significant reduction in microbial concentration.


Current results show a difference in microbial removal effectiveness between the new and used filter. The old filter still removes bacteria at close to a 2-log reduction. Thus, there is evidence of long term sustainability of the Filtrón. The project, thus far, has established sustainable effectiveness of the POU device, the Filtrón, for effective removal of microorganisms from drinking water. Clean, safe drinking water is essential to both human health and economic security, so the project has and will continue to evaluate the long term performance of a device that provides this essential need.

There is still much work that needs to be done. Additional research objectives of our study include the evaluation of filtration rate, evaluation of methods to regenerate or extend the use life of the Filtrón, assessment of microbial regrowth in the filters, and evaluation of different initial colloidal silver coatings. If the filters clog and the flow rate decreases substantially, families can not rely on the filters to produce a sufficient amount of water for their needs. If the silver slowly leaches out of the filter and decreases effectiveness, then an evaluation of what methods are needed to regenerate the capacity of the filter including scrubbing, or reapplication of colloidal silver.

Supplemental Keywords:

drinking water, pathogenic microorganisms, disinfection, filtration, point-of-use, household, RFA, Scientific Discipline, Water, Environmental Chemistry, Drinking Water, Environmental Engineering, alternative disinfection methods, pathogens, sustainable development, ceramic filters, filtration, disinfection of waters, microbial risk management, point of use, drinking water treatment