Aerating static mixers prevent fouling

Abstract

To mitigate fouling and reduce concentration polarization at membrane surfaces, various measures have been investigated. One approach is to alter the hydrodynamics in a tubular membrane by inserting static mixers, which disturb the flow, enhance particle back-transport and increase the shear rate at the membrane surface. Another approach widely applied in wastewater treatment, but not limited to this application, is air sparging. Combining both measures - air sparging and static mixers - yields a novel device to mitigate fouling in tubular membrane filtration: aerating static mixers.Aerating mixers are static mixers with an incorporated air channel. They can be fabricated in one piece by means of 3D-printing. Thanks to the incorporated air channel, aerating mixers are able to direct air bubbles straight towards the membrane surface. That way, the fouling mitigation potential of static mixers is enhanced by the application of two-phase flow. We demonstrate that aerating mixers reduce fouling to a greater extent than static mixers or air sparging alone. Furthermore, we show that the novel aerating Kenics is superior to a Kenics mixer combined with air sparging from an external source. With the aerating Kenics, the total membrane resistance stayed nearly constant for the investigated range of fluxes, which reached up to 353LMH. Due to the significantly reduced TMP required to obtain the desired permeate fluxes, the systems where a static mixer was applied showed the lowest specific energy consumption. In case of the systems with air, the energy to compress the air contributed less than 13% to the total specific energy consumption.