Effect of bubble size – Hollow fiber membrane

According to the data available from the public domain, small bubbles are more effective for short hollow fiber membranes (110-400 mm) and tightly held long hollow fiber membranes (820 mm)than large bubbles at a same air flow rate. However, large bubbles appear more effective for long hollow fiber membranes held loosely, e.g. ZW500dTM, SADFTM, etc. […]

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Effect of bubble size – Flat sheet membrane

In flat sheet submerged membrane, membrane panels are stacked against each other with 5-7 mm spaces in between two panels. All the bubbles released from the diffusers located underneath the membrane panels rise through the in-between spaces while physically contacting with membrane surface. Large bubbles are likely more effective in membrane scouring due to the […]

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Air flow rate vs fouling rate

As expected intuitively, membrane fouling rate can be mitigated by increasing scouring air flow rate in immersed membrane process. Air bubbles not only contact directly with membranes, but also increases bubble induced water flow on membrane surface. In addition, in the case of hollow fiber membrane, rising bubbles also increase random fiber movement that causes […]

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Fundamentals of air scouring

Mechanism Air sparging induces shear forces at the membrane surface as rising air bubbles travel near the membrane. The shear forces increase the mass transfer in the concentration polarization layer on membrane surface, which facilitates particle transport away from the membrane surface. Two mechanisms are predominantly responsible for the high surface shear forces in both […]

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Fundamentals of air scouring in MBR

Overview The permeability decline associated with particle deposition on the membrane surface is a major hurdle in membrane filtration. In traditional crossflow filtrations using pressure vessels and circulation pumps, membrane fouling could be controlled reasonably using high cross flow velocity, but excessive energy costs and negative impacts on microorganisms by pump shear stress were the […]

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