Development of continuous marine microalgae harvest system by use of electrolysis

Abstract

Recently, microalgae have received much attention as an attractive biomass for the commercial production of advanced biofuels, including biodiesel and aviation fuels. Despite the various benefits associated with the production of biofuels using microalgae, the cost of microalgal biofuel production is still significantly higher than that of fossil fuels. Downstream processes for microalgal biodiesel production commonly includes cultivation, harvest, extraction and conversion steps. For the economic feasibility of microalgal biodiesel, each downstream process should be economic and simplified. In this study, the continuous microalgal harvest system (combined algal cultivation and harvest steps) was designed to reduce biodiesel production cost and water footprint. The harvest methods such as continuous centrifuge and cross flow filtration can be applied to this type of continuous system. However, these technologies face high operating expenses which frustrate an economical microalgal harvest for the biodiesel production. Herein an electrolysis-based harvest technique as a new alternative was applied in the continuous system. Electrolysis-based harvest technique requires lower operation cost compared to continuous centrifuge and cross flow filtration. Also, both polyvalent metal ions and microbubbles generated during electrolysis result in the fast and efficient algal flocculation compared to chemical coagulants. Neutral pH of medium during and after harvest would be another advantage to apply electrolysis-based harvest technique in continuous harvest system. To achieve the feasibility of an electrolytic harvest method in continuous harvest system, the electrodes were subject to a polarity exchange (PE, changing current direction) in the middle of the operation. PE creates two distinct phases, electro-coagulation (phase 1) and electro-flotation (phase 2) simply by changing the polarity of a pair of metal and inert electrodes. In continuous system, better harvest ...