Power induced by bubbles of different sizes and frequencies on to hollow fibers in submerged membrane systems

To shed light onto the relationship between sparging conditions and fouling control in submerged hollow fiber membranes, the effects of bubble size and frequency on the hydrodynamic conditions induced in membrane system were studied. Two general classes of bubbles were considered: coarse (0.75–2.5 mL) and pulse (100–500 mL). The power transferred (Ptrans) onto membranes could be used to characterise the multiple effects induced under different sparging conditions. Ptrans is proportional to root mean square of shear stress (τrms), the area of zone of influence (i.e. the fraction in the system where high velocity and high vorticity (turbulence) are induced by the bubble) and their rise velocity. At a given sparging rate, the power transferred onto membranes was less with coarse bubble sparging than pulse bubble sparging and increased with the size of pulse bubbles. For all cases, the power transfer efficiency was consistently higher for pulse bubble sparging than for coarse bubble sparging. The power transfer efficiency to the system was greatest for the small pulse bubbles considered when a small amount of power is required for fouling control. However, when fouling is extensive, large pulse bubbles may be required to generate the required amount of power for fouling control. [Display omitted] •Power transferred can be used to quantify the effectiveness of air sparging for fouling control.•Power transferred onto the membranes was affected by sparged bubble size & frequency.•The resulting power transfer efficiencywas affected by sparged bubble size & frequency.•Significantly greater power transfer efficiency for pulse bubble than for coarse bubble sparging.