Distribution of surface shear stress for a densely packed submerged hollow fiber membrane system

• Surface shear stress was characterized for different air sparging of a UF module.
• Shear stress was greatest on the outside plane of a densely-packed membrane module.
• Pulse bubble sparging was most efficient (high shear stress at low air flow rates).

Surface shear stress induced by different air sparging regimes on a submerged hollow fiber ultrafiltration module with horizontally-oriented, densely packed fibers was characterized. Continuous and intermittent (cycling on and off) coarse bubbles (0.75–2.5 mL), as well as large pulse bubble (150 and 500 mL) sparging were considered for a range of air flow rates. The power required to induce surface shear stress on the surface of the hollow fibers was substantially lower when using large pulse bubble sparging compared to both continuous and intermittent coarse bubble sparging. Results indicated that the air flow required for pulse bubble sparging was more than 80% lower than that required for coarse bubble sparging to induce comparable surface shear stress (and corresponding fouling control). This study demonstrates the potential value and efficiency of pulse bubble air sparging as a fouling control option in densely packed hollow fiber membrane systems.