Direct filtration of natural and simulated river water with air sparging and sponge ball application for fouling control

Membrane filtration is increasingly used for converting surface water to drinking water. This study investigated the effectiveness of air sparging in reducing fouling during direct membrane filtration of river water. Air sparging via side-stream filtration in tubular membranes at crossflow velocities (CFV) between 0.5-1.0 m/s enhanced the permeability by up to a factor of 4.6, given that the water used showed a high propensity of fouling. Sponge ball application to remove fouling proved, for model solutions with silt and clay, that chemical cleaning with NaOCl cannot erase fouling on the membrane surface by 100%. Residual fouling, indicated by flux increase above the initial flux observed after sponge ball cleaning, remains. Repeated sponge ball application appears to reduce the residual fouling. In terms of seasonal water sampling, the fouling potential declined from spring to fall due to a decrease of natural organic matter (NOM), colloids and mineral load (indicated by total organic carbon and turbidity). Air sparging (AS) effectiveness, measured by the ratio of AS-enhanced versus non-enhanced permeability, decreased with the dwindling fouling potential of the raw water. When model solutions were investigated (silt 5 g/L and clay 10 g/L), the enhancement factor for the silt slurry was less than that for the clay.