Ultrafiltration (UF) is increasingly used for potable water treatment, but membrane fouling necessitates the application of periodical backwash, which increases running cost. A new backwash strategy, in which air scouring was only applied with sludge water discharging, was proposed to improve backwash performance in a water plant using UF. Four gravity-driven UF systems were simultaneously run at increasing air scouring intervals (3–24hours) and sludge water discharging intervals (12–24hours). The membrane fluxes were monitored to assess membrane fouling and the mix solution turbidity was also monitored to investigate deposition of particles. The results indicated that membrane fouling was not aggravated by the extension of air scouring and sludge water discharging intervals. Water backwash on its own induced a shift of particle deposition from the membrane surface to the bottom of the membrane tank due to limited cake layer breakage, enabling the extension of sludge water discharging intervals. For the gravity-driven system investigated, the running cost, including energy, water and chemical demand, was reduced by 16.67% as the air scouring and sludge water discharging intervals increased from 3hours to 24hours and from 12hours to 24hours, respectively.

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