Polyacrylonitrile membranes for microalgae filtration: Influence of porosity, surface charge and microalgae species on membrane fouling

A comprehensive study on membrane fouling using polyacrylonitrile (PAN)-based membranes with different properties was performed for 8 microalgae species. Two sets of PAN membranes with different porosity and surface charge were prepared via phase inversion and further hydrolyzed to introduce a negative charge on the membrane surface. These membranes were then used for filtering microalgae which differ in a number of properties and are characterized by their dry weight, size, shape, presence of cell-wall, zeta potential, and transparent exopolymer particles (TEP) content. For most species, more fouling occurred in the more porous membranes. Negatively charged membranes offered species dependent benefits to reduce fouling. Remarkably, this benefit seemed to be partially influenced by TEP concentration, but not by the zeta potential of the microalgae. The results also show that fouling in microalgae filtration is dominated by the formation of a cake layer by the cells which is mainly influenced by cell shape and size, size distribution, and cell-wall rigidity. It was found that microalgae with non-spherical (Scenedesmus and Phaeodactylum), larger size and a rigid cell wall filtered better than those with no cell wall (Isochrysis) or a flexible one (Pseudanabaena), proven by their cake resistance values.