Colloidal- Ag -impregnated alkali-activated foams for point-of-use water disinfection
Alkali-activated materials are a new potential alternative to conventional ceramics in point-of-use water disinfection. Alkali-activated materials are prepared from industrial side streams or natural minerals at low temperature but have similar properties to conventional ceramic filter which is widely used for water disinfection. In this study, alkali-activated foams with different compositions were prepared by using the direct foaming method. Their porosity was adjusted to result similar water permeability as with typical point-of-use ceramic filters. The foams were characterized for their mechanical strength and shrinkage. The optimized foam (based on metakaolin) was coated with colloidal Ag solution and its chemical stability (i.e., leaching of Ag, Na, Si, and Al) was studied. The disinfection performance of the foams with and without Ag were investigated in a 10-week experiment, where clean water was pumped through the foams continuously with a municipal wastewater pulse once per week. The inactivation of Escherichia coli from wastewater was 2.84 log10 for Ag-modified foam, which was 1.27 units higher than blank foam. Moreover, from DNA based methods it was observed that both foams with and without Ag were effective in reducing microbial load from the influent wastewater. Furthermore, the changes in community composition, antibiotic resistome and metal and biocide resistome by the foam with Ag was significant.   The environmental impact of alkali-activated foam compared to conventional ceramic filter was evaluated by life cycle assessment.