The effect of sawdust on the pore structure and properties of low-cost ceramic water filter materials

Abstract

Low-cost ceramic water filters are a very effective point-of-use technology for removing bacteria and protozoa from drinking water. The filters are made from locally sourced clay and a porogen materials such as sawdust. It is recommended that the sawdust be sieved to 30-sieve (600 μm) to make reliable filters. However, the size distribution of sawdust is usually broad and can extend below 100 μm. This study divided 30-sieve sawdust into four narrower size distributions and made filter disks for measurement of hydraulic conductivity and bulk density. Additionally, the microstructure of the materials was examined in three dimensions by micro-CT. The results showed that, independent of sawdust particle size, the void volume fraction in the filter increased linearly with the weight fraction of sawdust. In contrast, the permeability coefficient increased non-linearly as the fraction of sawdust increased. The magnitude of the permeability was higher for the larger sawdust particles when the sawdust fraction was 10 wt% or higher. Three-dimensional imaging of the pore structure in the filters suggested that the non-linear increase in permeability with increasing weight fraction of sawdust may be associated with increased interaction of the cavities created by the sawdust.