Biofouling metallic membranes in algae-laden water treatment: Performance, mechanism, and the role of the pre-coated layer

Abstract

Biofouling is the primary factor limiting the performance of ultrafiltration membrane systems in drinking water treatment. This study systematically investigated the application effect and biofouling behavior of metallic membranes in the treatment of algae-laden water and evaluated the mitigation effect and mechanism of the pre-coated layer on biofouling. The findings demonstrate that the metallic membrane can almost completely remove algal cells (>99.99 %) and macromolecular organics in EOM (Extracellular Organic Matter) but has limited effects on micromolecules, such as humic acid and fulvic acid, in EOM (47.29 % and 17.72 % for TOC (Total Organic Carbon) and UV254, respectively). During direct filtration, algal cells can form a cake layer in front of the metallic membrane to reduce the membrane flux, whereas the presence of EOM makes the cake layer denser and hastens the decline in flux. In addition, irreversible membrane fouling is exasperated in acidic or Ca2+-rich solutions, whereas an increase in algal cell particles exacerbates reversible membrane fouling, causing a faster decline in flux. According to the membrane mechanism analysis, the fouling mechanism ranges from complete pore blocking to standard and intermediate blocking throughout the direct filtration process. In contrast, the application of a pre-coated kaolin layer significantly decreases membrane fouling compared with direct filtration. The pre-coated layer can prevent direct contact between the foulants and the membrane surface during the early stages of filtration, resulting in a delayed complete pore blockage stage. On the other hand, XDLVO (Derjaguin-Landau-Verwey-Overbeek) data reveals that the force between kaolinite and algae (−102.323 mJ/m2) is greater than that between kaolinite and metallic membranes (−61.424 mJ/m2), resulting in better backwashing efficacy. These findings support the use of metallic membranes in drinking water treatment.