Removal of colloidal particles in ceramic depth filters based on diatomaceous earth

Safe drinking water is still not accessible to more than 15% of the world's population. Decentralised water treatment with ceramic filter candles at the point-of-use (POU) level provides a low-cost and single-stage filtration process with which pathogenic microorganisms can be removed. However, the retention performance of such depth filters scatters for microbiological contaminants in literature. The purpose of this study was to gain a better understanding on the removal mechanisms in ceramic depth filters based on the natural material diatomaceous earth (DE). Therefore, we manufactured so-called ceramic filter candles by ram-extrusion process and subjected these filters to a detailed physical characterisation regarding porosity, pore size distribution, specific surface area, flowrate, surface charge and microstructure. Next, we investigated experimentally the removal of colloidal latex (polystyrene) particles having diameters from 100 to 500 nm under various ionic strengths. Such particles were found to be removed due to adsorption of the colloids. Extended DLVO-theory was used to investigate the forces that account for the adsorption suggesting that hydrophobic interactions drag latex particles onto specific adsorption sites of the filter. It is hypothesised that these specific adsorption sites originate from the unique nano-structured surface of the diatomaceous earth. Furthermore, we believe that such latex particles may be suitable to model the removal of microorganisms if the surrogate and the target pathogen have similar characteristics. (C) 2011 Elsevier B.V. All rights reserved.