Removal Mechanisms of Contaminants in Ceramic Water Filters

In this paper, the removal mechanisms of organic (e.g., nitrate) and inorganic (e.g., lead) contaminants were investigated in ceramic water filters with organic (i.e., activated carbon) and inorganic (i.e., hydroxyapatite) additives. The ceramic water filters were characterized using atomic force microscopy, nitrogen sorption analysis, X-ray pair distribution function analysis, and scanning electron microscopy. It was found that adhesion controlled the efficiency of the ceramic water filters in the removal of contaminants. The conventional ceramic water filters had no adhesive interactions with the contaminants. A small amount of contaminants was removed by physical trapping in the pores. However, the addition of organic additives increased the adhesion between the organic contaminants and ceramic water filters (i.e., from 16 to 170 nN). This resulted in an increase of the efficiency from 0.9 to 6.7 mg·g-1 in the removal of nitrate for a 20 wt.% addition of activated carbon. The removal of nitrate was completed once the surface was fully covered (surface adsorption mechanism). It was limited by the specific surface area of the materials. On the other hand, the inorganic additives increased the adhesive interactions of the ceramic water filters with the inorganic contaminants (i.e., from 33 to 153 nN). The efficiency in the removal of lead increased from 12.2 to 67.1 mg·g-1 with a 2 wt.% addition of hydroxyapatite. The removal was achieved by substitution of lead atoms (Pb) for calcium atoms (Ca) in the hydroxyapatite. Hence, the novelty of this work lies in the fact that doped ceramic water filters remove a wide range of contaminants from water via the combination of trapping, adsorption, and substitution mechanisms. Such filters are also suitable in terms of mechanical performances (i.e., 8.7 MPa) for application in household water treatment.