Characterization of stone powder sludge foams and their application to wastewater treatment: Role of pore connectivity

Ceramic foams with different relative densities (i.e., different extension ratios) were successfully prepared from stone powder sludge (SPS) via a foaming and gelcasting method. Ceramic foams with various relative densities were characterized in terms of porosity, specific surface area, and water absorption capacity. The porosity of the ceramic foams ranged from 35% to 78%, depending on the extension ratio. The specific surface area and water absorption capacity increased as the relative density decreased (i.e., increasing extension ratio), resulting in enhanced pore connectivity. The feasibility of the SPS foams as microorganism-immobilized carriers and the effect of inner pores on simultaneous nitrification/denitrification were tested through wastewater treatment experiments. The results from fixed-bed reactors packed by SPS carriers with different relative densities revealed that the organic removal efficiency for all reactors was greater than 90%. In addition, the nitrification/denitrification experimental results suggested that the increase of the NH4+-N loading rate resulted in the improvement of nitrification efficiency and the decrease of nitrogen loss in all reactors. However, no significant correlation between relative density (i.e., extent of inner pore development) and nitrification/denitrification efficiency was found.