Investigating submerged ultrafiltration (UF) and microfiltration (MF) membranes for seawater pre-treatment dedicated to total removal of undesirable micro-algae Original Research Article

In this study, an original use of low-energy-consuming submerged MF/UF membranes was investigated for the total removal of toxic micro-algae (Alexandrium sp.) from seawater. Experimentally, a non-toxic micro-alga (Heterocapsa triquetra) which has morphological and dimensional (15–20 µm) similarities with Alexandrium sp., one of the smallest toxic micro-algae in seawater, was ultra- and micro-filtered. A lab-scale membrane screening was operated on 10 kDa, 300 kDa and 0.2 µm membranes by filtration of 30,000 cells mL− 1 of H. triquetra suspension (equivalent to a major natural phytoplanktonic bloom). The most promising results were obtained with microfiltration membrane (0.2 µm): the highest steady state permeate flux reached 29 L h− 1 m− 2 under 0.3 bar of transmembrane pressure after 180 min of filtration. More than 99%, 87% and 98% of micro-algae, Total Suspended Solid (TSS), and turbidity were eliminated, respectively. Combining hydraulic permeability versus time with modified fouling index (MFI) determination and membrane autopsy (FEG-SEM and AFM observations), it is observed that fouling is mainly due to cake formation.