The effect of compositional and geometrical changes to the bending strength of the Ghanaian ceramic pot filter

Abstract

Pure Home Water (PHW) is a non-profit organization with the goal of providing safe drinking water through household water treatment and storage (HWTS) to the inhabitants of Ghana, particularly in the Northern Region. To this end, PHW has pursued the distribution and training in the use of the Kosim ceramic pot filter (CPF), and now wishes to pursue its manufacture. Laboratory studies have found the CPF to be between 97.8 and 100% efficient in the removal of E. coil bacteria. One of the main reasons for a household's discontinued use of the CPF is breakage. In a follow up monitoring of 1,000 homes receiving CPFs after an emergency flood distribution in 2008, the rate of breakage was found to be 12%. To address this critical problem, the author performed a three-point bending test on rectangular-prism clay samples with varying recipes and thicknesses in an attempt to determine bending strengths associated with the recipes with the aim of moderating the lip failure due to the possible failure mechanism of bending stress. Filter recipes were assigned numbers 1 through 14 based on combustible type, presence or absence of grog, combustible volume, and manufacturing process. The recipes which incorporated only fine, sieved combustible materials yielded the highest mean bending strengths. Statistically significant decreases in bending strength were realized with the increase of combustible mass. The inclusion of grog was generally found to have no statistically significant impact on the bending strength. Experimentally observed gains in bending strength with increased thickness supported theoretical strength gains with the square of the thickness. The variable of firing condition was found to be a significant but unquantifiable variable in the bending strength of the samples. In all cases, the lower bound of a 95% confidence interval of the mean bending strength of the materials was found to exceed the expected bending stress on the filter lip due to predicted loading conditions. It is recommended that PHW pursue the manufacture of a fine-and-waste rice husk recipe with a 3:8 combustible-to-clay ratio without the inclusion of grog. It is recommended that the lip of the filter be thickened to 25 mm. It is recommended that pyrometric cones be placed in the spy-hole and door of the kiln during each firing and monitored once an hour until the guide cone bends, and once every fifteen minutes thereafter until the firing cone bends, at which time firing should cease. It is recommended that consultation with kiln designer Manny Hernandez be maintained so as to create even firing conditions within the kiln.