Dewatering of microalgae suspensions by cake filtration with filter cloths

Abstract

Microalgae are a promising bioresource because they produce various materials that can be used as fuels, nutraceuticals, cosmetics, and pharmaceuticals. Additionally, microalgae production is not highly competitive with food production. However, it is quite expensive to harvest microalgae because they are small and suspended in culture broth at dilute concentrations during cultivation. Many studies have been conducted to develop a cost-effective and energy-efficient system for the harvest of microalgae. In this study, cake filtration of a microalgae suspension with a filter cloth was investigated, which is an inexpensive method compared with using conventional microfiltration and ultrafiltration membranes. Because particles deposited on the membrane serve as a secondary membrane during cake filtration, no expensive membrane is needed. To perform cake filtration under optimum conditions, the effects of filter cloths with different pore sizes (0.8–14 μm) on the filtration performance were examined using a constant pressure filtration apparatus. Moreover, filtration behavior was analyzed using existing filtration models. The results showed transition of filtration modes from blocking filtration to cake filtration as the process progressed. Based on these results, we proposed filtration of a preconcentrated suspension using a rough filter cloth having a pore size larger than the algal cell size and then verified the system. Using this system a high solid concentration of cake (18.4 wt%), which was desirable for subsequent processing, was achieved. Furthermore, both relatively high permeate flux and low solid contents in the filtrate were achieved by cake filtration.