Microfiltration of Chlorella sp.: Influence of material and membrane pore size

Four membranes were used to separate Chlorella sp. from their culture medium in cross-flow microfiltration (MF) experiments: cellulose acetate (CA), cellulose nitrate (CN), polypropylene (PP) and polyvinylidenefluoride (PVDF). It was found that the hydrophilic CA and CN membranes with a pore size of 1.2 ${\mu}m$ exhibited the best performances among all the membranes in terms of permeation flux. The hydrophobicity of each membrane material was determined by measuring the angle between the water (liquid) and membrane (solid). Contact angle measurements showed that deionized (DI) water had almost adsorbed onto the surfaces of the CA and CN membranes, which gave $0.00^{\circ}$ contact angle values. The PP and PVDF membranes were more hydrophobic, giving contact angle values of $95.97^{\circ}$ and $126.63^{\circ}$, respectively. Although the pure water flux increased with increasing pore diameter (0.8 < 1.2 < 3.0 ${\mu}m$) in hydrophilic CA and CN membranes, the best performance in term of filtration rate for filtering a microalgae suspension was attained by membranes with a pore size of 1.2 ${\mu}m$. The fouled membrane pore sizes and pore blocking were inspected using a scanning electron microscope (SEM). MF with large pore diameters was more sensitive to fouling that contributed to intermediate blocking, where the size of the membrane pores is almost equivalent to that of cells.