Abstract for: AICHE Student Conference, Salt Lake City, UT, November 6 – November 9, 2015
Towards Water Disinfection using Silver Nanoparticle-Modified Ceramic Membranes
Michael F. Desmarais1, Vinka Oyanedel-Craver2, Geoffrey D. Bothun1
1Department of Chemical Engineering, University of Rhode Island, Kingston, RI
2Department of Civil & Environmental Engineering, University of Rhode Island, Kingston, RI
Every year, more than 840, 000 people die globally from water related diseases. To address this challenge, particularly in developing countries, effective low-cost technologies are needed for water disinfection. A promising approach is to integrate these technologies within household water treatment and storage (HWTS) systems, such as ceramic filters made with indigenous materials. Previous work has shown that HWTSs with clay filters can achieve partial water disinfection when the filters are treated with colloidal silver – the colloidal silver deactivates the bacteria and leads to an approximate 2-log reduction in bacteria concentration. While effective, (1) ceramic filters made from clay exhibit large variability in porosity and pore size, which make it difficult to predict flux and biofouling behavior, and to determine mechanisms of bacterial reduction. Furthermore, (2) colloidal silver is often physically-adsorbed onto the filters, making it difficult to control the spatial organization within the filters and causing it to leach out.
To address these limitations, the first goal of this project is to determine flux and evaluate fouling layer growth using well-defined ceramic membranes with and without physically-adsorbed silver nanoparticles (AgNPs; 95 nm diameter coated with polyvinylpyrrolidone, or PVP). The ceramic membranes were composed of a zirconia (ZrO2) support layer with a titania (TiO2) active layer with a pore size of 1.4 µm. Membrane permittivity was measured by dead-end filtration with and without AgNPs in the absence and presence of E. Coli. Inlet and outlet samples were colonized on agar plates to compare the bacterial reduction between the trials with and without AgNPs. For both membranes the results were comparable, indicating that the bacteria that passed through the membranes were not deactivated by AgNPs. This result suggests that AgNPs either inhibit bacteria contained within the biofilm that make direct contact with the AgNPs on the membrane surface, but they do not deactivate bacteria in the permeate, or that proper adherence of AgNPs to the ceramic surface was not achieved. The membranes were also examined by scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS) to observe the biofilms and silver distribution.
The second goal of this project is to examine a new templating method for forming AgNPs on the same membrane surfaces. In this method, AgNPs were formed on ceramic membranes coated with polydopamine through the reduction of silver nitrate at reaction times of 15, 30, 90, and 180 min. For all samples, noticeable coloration differences were observed when compared to ceramics without AgNPs confirming AgNP formation. Preliminary results for the polydopamine method are promising and show that AgNPs can be formed on the surface of ceramic membranes. Additional experiments are being conducted to determine the optimal conditions for AgNP formation and to evaluate the membrane flux and fouling behavior.
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