In this study, the combination of capture mechanisms in ceramic water filters (doped with hydroxyapatite and alumina) was considered for the removal of contaminants from drinking water. It was found that hydroxyapatite and alumina were conserved during the firing process of the ceramic water filters up to 950°C. The nanopores resulting from the conservation of the additives increased the specific surface area of the ceramic water filters from 3.7 to 21.0 m 2 · g −1 . On the other hand, the microscopic pores associated with the processing of the ceramic water filters (i.e., pressing and drying) and the combustion of the sawdust reduced the filtration time from 24 to 4 h. The efficiency of the resulting filters in removing bacterial, chemical, and viral contaminants from water was investigated using E. coli, fluoride, and MS2 as model contaminants. The contaminants were found to be captured from water by trapping in the pores, substitution in the hydroxyapatite, and adsorption on the surface of alumina. Hence, the ceramic water filters incorporating hydroxyapatite and alumina combined the different capture mechanisms. They had an efficiency of 99.998%, 99.970%, and 99.450% in the removal of bacterial, chemical, and viral contaminants, corresponding to log reduction values (LRVs) of 4.69, 3.47, and 2.26, respectively.
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.
A clay ceramic with organic additives (biomass and biochar) was investigated for the development of highly porous accumulators to capture heavy metals in thermal conversion systems. The structure was characterized using X-ray pair distribution function analysis, differential scanning calorimetry, and scanning electron microscopy. It was found that the organic additives transformed into porosity during firing. The morphology of the pores also corresponded to the morphology of the organic additives. Hence, the clay ceramic with a 15-wt% addition of biochar had a porosity of 46 vol% with 20-μm interconnected pores after firing. The resulting accumulator was found to capture cadmium (a model for heavy metals with high volatility) via condensation of the cadmium vapor as 2-μm beads in the pores. The cadmium capture efficiency reached up to 57% using a 15-wt% addition of biochar. Furthermore, cadmium was captured at higher temperatures than the condensation temperature in the atmosphere. This means that heavy metals may be captured before they condense in fly ash to promote the recycling of this material.
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