New Method for the Deposition of Metallic Silver and Metallic Copper on Full-Size Porous Ceramic Water Filters

Abstract Performance of a new method for the deposition of metallic silver and metallic copper in ceramic water filters was investigated. Ceramic water filters were manufactured at two PureMadi filter production facilities in South Africa. Silver or copper was applied to the filters in solution as silver or copper nitrate AgNO 3 or Cu(NO 3 ) 2 and mixed with clay and sawdust. The mixture was pressed into a pot shape and fired in a kiln. During firing the ionic silver or copper is reduced to metallic nanopatches dispersed through the porous ceramic media. For comparison testing, filters were also manufactured using a conventional silver application method consisting of painting an aqueous suspension of silver nanoparticles (AgNPs) onto filters postfiring. Resulting filters were evaluated in flow-through experiments and in stagnant water experiments (to consider a worst-case scenario for silver release). Flow-through experiments quantified total coliform and Escherichia coli removal and metal concentration in the effluent. Total coliform and E. coli removal was greater for AgNO 3 filters (log reductions of 4.06 and 4.11) relative to AgNP filters (log reductions of 3.85 and 3.92). AgNO 3 filters also resulted in lower silver concentrations in the effluent, potentially increasing the effective life span of the filter. Filters made with Cu(NO 3 ) 2 performed slightly worse than AgNP filters, but were still effective with log total coliform and E. coli removals of 3.33 and 3.54, respectively. The new method of silver application could potentially reduce production costs, improve performance, and increase safety of production for workers.