Ultrafiltration and microfiltration membrane performance, cleaning, and flux recovery for microalgal harvesting

Membrane material, pore size, and cleaning strategy are important factors for microalgal membrane harvesting. In this study, harvesting of Scenedesmus acuminatus cultivated in pilot scale using nine ultrafiltration and three microfiltration membranes was carried out in cross-flow filtration system to compare their filtration performance and flux recovery after physical and chemical cleaning. The 0.45-μm PVDF-AsahiKASEI membrane had the highest average flux of 513.6 L m −2 h −1 among 12 membranes and 50-kDa PVC-Litree membrane had the highest average flux of 98.0 L m −2 h −1 among nine ultrafiltration membranes for 60 L S. acuminatus suspension harvesting. There were significantly positive correlations between membrane pore size, pure water flux, and average flux for S. acuminatus suspension harvesting. Generally, ultrafiltration membrane had moderate total fouling index (TFI) and high proportion of hydraulic reversible fouling index (HRFI) of more than 95%. The 0.45-μm PVDF-AsahiKASEI membrane had a low TFI but the lowest proportion of HRFI, associated with the residual microalgal cells, debris, and colloids on the inner surface and top ends of some cells inserted to big membrane pores, demonstrated by SEM image and reduced porosity from 65.9 to 60.2%. Compared to soaking cleaning, circulation cleaning strategy had a better flux recovery efficiency for 0.45-μm PVDF-AsahiKASEI membrane, proving that it would be a potential way in membrane chemical cleaning. This study demonstrated that microfiltration with high flux has great potential in microalgal harvesting if flux recovery efficiency can be significantly increased using suitable cleaning strategy such as circulation cleaning strategy.