Crossflow microfiltration of microalgae biomass for biofuel production

Abstract

Crossflow microfiltration (MF) was successfully implemented for harvesting microalgae suspensions from a culture medium. In this study, investigations were carried out to harvest Chlorella sp. using a cellulose acetate (CA) membrane. Electrophoretic mobility profile during the cultivation process showed a maximum electronegative value of −2.56±0.07μmcm/Vs on the 9th day of the experiment which were taken as a fresh cultures in each cultivation process. The effects of hydrodynamic conditions on the permeation flux are also discussed. The results show that the permeate flux increases with an increasing crossflow velocity (CFV) and transmembrane pressure (TMP). The flux is higher when the pressure is high, suggesting that the resistance of the membranes to mass transfer increases; hence, the applied pressure (driving force) has to be increased to obtain a higher flux. Furthermore, an increase in the CFV leads to a higher shear velocity, which makes it more difficult for microalgae to be deposited on the membrane, thus giving a better flux. The analysis of various resistances encountered in membrane filtration which involves the resistance of membrane itself and cake as well as those due to pore blocking and concentration polarization was studied. The experimental results obtained here show that the cake resistance (Rc) played a more major role in the filtration rate than the resistance due to concentration polarization (Rcp) and pore blocking (Rb) under the conditions examined. An increase in the CFV and a decrease in the TMP result in a reduction in the cake layer formation.