A comprehensive approach to simulation of cartridge filtration using CFD

Household water treatment (HWT) systems are widely used for the provision of potable water in many countries with their low-cost key to attaining universal and equitable access to safe and affordable drinking water, Sustainable Development Goal 6.1. Removal of suspended particles (turbidity) from water sources via cartridge filters is often the first step of a HWT system, with the primary treatment increasing the efficiency of a subsequent disinfection step. Whilst the performance of cartridge filters (removal efficiency and pressure drop) can be determined experimentally in long experiments with high volumes of water, numerical simulation adds fundamental insight to the influence of fluid dynamics on particle deposition and vice versa. In this study, a novel computational fluid dynamic (CFD) model was developed to simulate the fundamental mechanisms underpinning the removal of particles within the widely used 10 in. cartridge filter, informed by and complemented with laboratory validation. The Eulerian approach was used to simulate fluid flow with the Lagrangian approach adopted for particle tracking. Rosin-Rammler distribution was implemented with respect to the particle size distribution of the diatomaceous earth particles used in the experiments. Given particles were non-spherical (disk shape), Wadell's sphericity was included to account for the effect of particle shape on drag force. A porous domain was implemented to simulate the filter element through addition of a source term to the momentum equations, with the likelihood of particle deposition, detachment and rebound also considered. Laboratory based validation studies confirmed the novel CFD model to accurately model removal of turbidity and predict the pressure drop across the filter with Root Mean Square Percentage Error (RMSPE) of less than 3%. The simulated location of particle deposition on the filter elements closely matched images taken at several stages during filtration experiments with the model aiding understanding of pattern of particle removal along and within the porous filter structure. This novel and comprehensive modelling methodology can be utilized to simulate the filtration process at the macro-scale, permitting evaluation of new filter designs and materials for advanced filtration systems; ultimately improving HWT system performance and reducing costs to users.