1. Impregnation of ceramic filters with silver nanoparticles View a poster of this research project. Silver is known to have an antibacterial effect, indeed this material has been used for this purpose for thousands of years (http://www.saltlakemetals.com/Silver_Antibacterial.htm). This material can be used in very small quantities due to an oligodynamic effect. Antibacterial action requires direct contact with the cell wall - as silver particles are adsorbed onto the bacterial surface. Heavy metal ions inhibit dehydrogenation, effectively deactivating the bacteria. The process denatures the enzyme proteins needed to reproduce. Since this is dependent on the surface of the cell wall coming into contact or near proximity with the silver the antibacterial effect is promoted if the silver is present as small nanoparticles with a high surface area per unit volume. Silver nanoparticles have been applied to low-cost ceramic water filters in a variety of ways including painting a nanofluid containing the particles onto surface of the filter. Alternatively, filters have been soaked in the silver nanofluid. When the nanofluid dries, the silver nanoparticles remain and are deposited on the clay structure. Controlled studies on the role of the silver nanoparticles in the antibacterial effectiveness of the filters have isolated the effect and shown that silver improves the already high capability of the ceramic filters to kill bacteria in the laboratory (V.A. Oyanedel-Craver and J.A. Smith, "Sustainable Colloidal-Silver-Impregnated Ceramic filter for Point-of-Use Water Filter," Environ. Sci. Technol. 42 927-933 (2008)). However, other studies conducted in the field and elsewhere have concluded that the treatment of the filters with nanoparticles has been less effective. It is not clear if these mixed results are associated with the differences in the impregnation techniques or the way in which the evaluations were conducted. It is apparent that greater physical understanding is required and standard practices must be developed for the manufacture and impregnation of the filters if more consistent results are to be obtained. In this project a team of students funded by the Mascaro Center for Sustainable Innovation examined the distribution of silver in ceramic filters that had been soaked in silver nanofluid. This work was performed on pieces of filter material that had been provided to the project by Professor Wukich of Slippery Rock University. The results were surprising in that the silver nanoparticles were found to segregate to the surface of the ceramic filter after the soaking procedure and during drying. In this circumstance the particles could easily be removed from the ceramic during scrubbing of the filter surface, a recommended step for maintenance. Additionally, the results of the soaking will be sensitive to the way in which the filter was dried. For example, drying in a steam of warm air will cause more evaporation on the surfaces of the filter most exposed to the dry air and this will cause more of the silver to segregate on these parts of the surface. Experiments are now underway to find new methods for improving the dispersion of the silver nanoparticles in the filter.
Figure 1: Segregation of silver on a filter sample 2. The use of ceramic filters on water boxes Houses in many countries around the world, including Brazil, have rooftop water boxes that store a quantity of water to ensure continuity of water supply. They are especially prevalent where there is no municipal water supply or the municipal water supply suffers from frequent drops in pressure.
Figure 2: Water boxes on the roofs of houses in a Brazilian favela
Unfortunately, the water boxes, if poorly constructed or maintained, can become a source of contamination even if the water entering the box is safe to drink ( Ilha, Marina. "Building and Water Systems." Oral Presentation: UNICAMP, Campinas Brazil. 9 June 2008.). The Pitt Ceramic Filter Project began an evaluation of ceramic filters for household water boxes. Previous studies of these filter materials have shown they can remove bacteria but the filtration rate is too low for water boxes. Calculations showed that a combination of additional head of water in the water box, geometry of the filter and a slight increase in permeability of the filter material would be enough to improve the flow rate to an acceptable level. However, the ability of the filters to eliminate bacteria at these new flow rates must be evaluated. Preliminary studies using a commercially available ceramic water filter purchased in Brazil showed that it was able to remove bacteria down to the minimum measurable level even though the flow rate was an order of magnitude higher than that measured for the PFP ceramic filters. Microstructural examination of this commercial filters (figure 3) showed that it did not contain the large cavities commonly caused by the addition of saw dust to the green clay in the PFP filter (figure 4). These results suggest that high flow rates are possible in clay derived ceramic filters without the large cavities that can easily compromise their strength, durability, and uniform performance. Research is currently being done to develop a procedure for clay processing that will result in more uniform microstructures and larger flow rates. This is also being explored as a means of controlling the distribution of silver in the filters as described above.
Figure 3: Microstructure of commercial Brazilian filter
Figure 4: Microstructure of the filter showing the large pores created by saw dust
For the Summer of 2008, our research focused on the concept of silver-impregnated ceramic water filters. Various aspects of the filter design and implementation were explored, including further work on silver location and impregnation methods. The theory of drying was applied to our study of current PFP filters. A PowerPoint summarizing the summer research can be downloaded below.
Download the presentation as a PDF file:
Summer 2008 Research Review (5.7 MB)
Upon the conclusion of the Summer '07 research experience, our research took an exciting leap forward. Dr. Ian Nettleship, a professor of Materials Science and Engineering, joined the project. Professor Nettleship had recently gained interest a simple, yet effective technology for the filtration of contaminated water. This filtration method, a ceramic water filter that has been impregnated with silver particles to filter particulates and kill bacteria in the water, is a technique currently practiced in developing countries, supported by an organization called Potters for Peace. Thus, through the 07-08 academic year, Curtis Larimer worked with this technology, observing the interactions between clay samples and various silver sources. A PowerPoint presentation of his results can be viewed below.
Senior Design Presentation - Curtis Larimer (1.8 MB)
The early focus of our research problem was to completely describe the drinking water system in Brazil. In doing so we were able to identify specific areas of need, lay out the parameters of each need, and deduct a solution. Fully describing the problem is the first step towards solving it. We have produced a PowerPoint presentation which summarizes our findings. Additionally, the presentation outlines some possible solutions that have been researched. After arriving in Brazil we were much more able to understand the subtleties of the drinking water system. We spent much of our research time in Brazil visiting facilities and companies related to the water system. We used the information gained to refine the goals of our project and succinctly summarize the challenges that lay ahead for drinking water in Brazil.
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IRES 2007 Final Presentation (1.8 MB)