Purification of harvested rainwater using gravity-driven ceramic membrane: A visualization study combining Micro-CT...

Rainwater harvesting is a viable solution for providing clean water in regions where conventional water sources are scarce or contaminated. However, the harvested rainwater often contains microorganisms, suspended particles, and other impurities that must be removed before consumption. Gravity-driven ceramic membranes (GDCMs) are an efficient choice for purifying harvested rainwater due to their energy-saving properties. Nevertheless, there is a lack of understanding regarding the impact of biofilms on the pore and seepage properties of GDCMs. In this study, we conducted a visualization investigation that integrated indoor seepage experiments with microcomputed tomography (micro-CT) and COMSOL simulations to delve into the fouling behavior and underlying mechanisms. The findings revealed that the growth of biofilm altered the surface pore structure of GDCM without impacting the internal pores. The surface pores of GDCM formed three specialized structures. Moreover, the probability density of small surface pore sizes increases substantially. It induced only subtle alterations to the coordination numbers, but resulted in a rapid reduction in the seepage flux. Simulation results indicate that the attachment of biofilms leads to the formation of high-pressure regions, primarily concentrated in the surface layer of less than 5% area. Here, the pores are abruptly constricted, and the pressure dissipates rapidly. As a result, the original seepage paths are obstructed, compelling the water to find and flow through longer alternative routes. To maintain a stable flux in the presence of biofilm, GDCM pore throat channels with different pore structures were evaluated, revealing that uniform channels were more effective than extremely complex channels.