A novel semi-empirical model for lifetime prediction of gravity based ceramic filter and permeability estimation

By reducing chemical, physical, and microbial contaminants, gravity-based ceramic water filters have proven to be a promising alternative for drinking water treatment. Acceptance of these filters, however, is contingent on a sufficient flow rate and the filtration efficiency. The lifetime and filtration efficiency of these filters depend on the active sites present at the internal surface exposed to the water in contact with the porous media and porous structure. The filtration rate of these filters is calculated using the Darcy equation. In literature semi–empirical relations are available between absolute permeability (K), porosity (ϕ), specific surface area (S) and Kozeny– Carmen constant (Ckc). Grain diameter and tortuosity can be calculated for these porous structures. In the present study, the Kozeny–Carmen constant (Ckc) is calculated for sintered ceramic material where the pore structure is difficult to approximate to a well-defined internal geometry. The sintered porous structure is obtained by mixing the clay material with an equal volume of sawdust in partially saturated water condition and sintered at a peak temperature of 850°C. Pore structure from the sintered material is digitally generated using micro-CT scanning at the machine resolution of 28.3 µm followed by image processing. Since sintered ceramic material exhibits pore space ranging from sub-micrometre to mm scale, low resolution scanning is used to capture the large region of interest (RoI). Digital geometries are simulated for the flow field inside the pore structure. Simulated permeability is calculated, which is compared with experimental permeability values. Results show that the permeability is a function of log normal porosity values. A correction factor (CF) is introduced and calculated for all simulated data to eliminate the error introduced in the simulated results due to the low resolution of the micro-CT scanner. From these results, an empirical relation between the permeability and porosity is determined. The predicted lifetime of a ceramic filter is based on the change in porosity caused by particle depth filtration and the corresponding pressure gradient available for gravity-based filtration at respective times during operation. Thus, a novel relationship between Kozeny–Carmen constant (Ckc) and porosity (ϕ) is proposed for predicting the lifetime of the ceramic water filter material.