Porosity, flow, and filtration characteristics of frustum-shaped ceramic water filters

This paper presents the results of an experimental study of the effects of porosity on the flow rate and Escherichia coli (E. coli) filtration characteristics of porous ceramic water filters (CWFs) prepared without a coating of silver. Clay-based CWFs were fabricated by sintering composites of redart clay and fine woodchips (sawdust) in three different proportions by volume, viz: 50:50, 65:35, and 75:25. Sintering the greenware below 1,000 C produced reddish colored pot of three different degrees of porosity and micro-and nanoscale pores, which are the key to efficient filtration. The porosities and pore size distribution frequencies of the sintered clay ceramics were characterized using mercury intrusion porosimetry (MIP). The porosity of the CWFs ranged from ∼36% to ∼47% and increased with increasing sawdust content in a linear fashion, and the pore size varied from ∼10 nm to ∼100 μm. The volume flow rates of water through the CWFs were investigated by measuring the cumulative amount of water flow as a function of time. The flow rate was found to increase with increasing porosity of the CWFs. The effective intrinsic permeabilities of the CWFs were then obtained from Darcy fits to the flow rate data. These were compared with values obtained using the Katz-Thompson method. Both approaches gave comparable results of permeability between ∼1 millidarcy to ∼50 millidarcy. The tortuosity of the CWFs was found from Hager's equation to range from ∼10 to ∼60. In general, while the permeability of the CWFs decreased with increasing clay content, tortuosity increased with increasing clay content. The CWFs removed E. coli from aqueous suspension very efficiently with average log reduction values between 5.7-6.4. The implications and limitations of the results are discussed for the effective filtration of water in the developing world.