Microalgae harvesting by an axial vibration membrane: The mechanism of mitigating membrane fouling

Membrane fouling by algae and extracellular organic matter (EOM) is a major problem in algae harvesting. In this study, the axial vibration ultrafiltration-membrane (AVM) is able to limit membrane fouling during filtration effectively. A membrane can achieve high critical flux at a high shear rate. During filtration, AVM is capable of operating with less fouling at a constant flux. The result from “extended Derjaguin, Landau, Verwey, Overbeek” (XDLVO) calculation indicates that with the increase of shear rate, it is more difficult for algae to foul the membrane. At a frequency of 5 Hz, the average inertial lift force is 0.024 nN, and the interaction force becomes a long-range attractive force that draws algae to the membrane; there are still certain smaller algae, algae debris and EOM that deposit on the membrane; leading to many algae depositing on the membrane. At a frequency of 10 Hz, the average inertial lift force is 0.12 nN, and there is a long-range repulsive region preventing algae from depositing on the membrane; however, the result shows that the mechanism of fouling mitigation by vibration is preventing algae from approaching the membrane, which reduces the deposition of algae on the membrane.