Air sparging backwash in ultrafiltration hollow fibres for drinking water production

Air sparging was applied to improve backwash efficiency for an ultrafiltration inside/out hollow-fibre module operating in dead-end mode. Air was injected into the retentate side only during the backwash period. The filtration experiments were performed on a semi-industrial scale pilot using a clay suspension as a model of surface waters. The backwash procedure consisted of two steps: in a first step (phase A), air was added to the feed water inside the fibre lumen at the bottom of the module. In a second step (phase B), cleaned water backwash was performed. Different air velocities were used and the kinetics of particle removal were studied with turbidity measurements of backwash waters. The experimental results showed that using an air-fluid mixing allows one to increase the quantity of particles removed from the hollow fibres. For the phase A, the removed mass is higher when the air velocity and duration of air injection increased. But, even at very low air velocity (0.08 m/s), a high backwash efficiency was observed. Experiments with filtration/air-sparging backwash cycles concluded that using air-fluid mixing in the backwash sequence allowed prevention of long-term fouling and reduced the rate of fouling during the filtration period.