Effects of microalgal concentration and pH with flocculant on microfiltration

Abstract

To make algal biomass a suitable feedstock for fuel and bioproducts, a practical way of dewatering and concentrating algal cells must be devised. In this study, a system comprising microfiltration membranes combined with a flocculant was developed on a low-cost ceramic substrate for efficient harvest of Tetradesmus obliquus. The effects of tannin-based flocculant concentration, microalgal concentration, and pH on microfiltration were studied. Permeate flux was evaluated for 5400 s through experiments to analyze the total resistance and the fouling mechanism. Results show that the cake filtration model best represented the data. The experiments at pH 4 and 0.06 kg/m3 of microalgae (with flocculant) showed improved results with reduction in J/J0 (permeate flux/initial flux) of 39%. In addition, the effects of critical flux, transmembrane pressure, and fouling mechanism on microfiltration were investigated under the best conditions studied. Application of the stepping method to the critical flux yielded permeate flux of 2.2 ? 10-5 m3m?2s?1. The 70 kPa condition showed the highest permeate flux (3.0 ? 10?5 m3m?2s?1) and a low cake pore blocking coefficient (k) obtained by the modified Hermia model. This study showed that the use of Tanfloc at low pH can maximize microalgal separation in membrane processes.