Increasing the vibration frequency to mitigate reversible and irreversible membrane fouling using an axial vibration membrane in microalgae harvesting

During algae harvesting using membrane technology, membrane fouling caused by the deposition of algae cells and extracellular organic matter (EOM) poses a major challenge. In this study, axial vibration membrane (AVM) filtration was conducted at 0, 5 and 10 Hz. As the frequency increased, AVM could effectively reduce the reversible fouling caused by the deposition of algae cells on the membranes. With the increase of frequency from 0 to 10 Hz in the 2-h filtration experiments, the amount of algae deposited on the membranes sharply decreased from 8.64 to 0.03 g/m2. For the reversible EOM on the membranes, with increasing frequency, the protein and polysaccharide contents exhibited declining trends, and no humic-like material was observed. It was also found that both low-MW (<1 kDa) and high-MW (>200 kDa) EOM easily caused reversible membrane fouling. The irreversible EOM adhesion to the membrane consisted of protein, polysaccharide and humic-like material. With the increase of frequency the MW peak of irreversible EOM had a right shift tendency. At 0, 5 and 10 Hz, EOM with MW of 3.5, 4 and 5 kDa, respectively, was more easily adsorbed on the membranes and caused irreversible membrane fouling.