Impacts of applied voltage on forward osmosis process harvesting microalgae: Filtration behaviors and lipid extraction efficiency

Abstract

Microalgae are promising source of biofuels, while harvesting process is the obstacle for the further development. Herein, a treatment system that combined electrochemical process with forward osmosis (FO) membrane filtration process was developed to achieve microalgae harvesting. The conductive FO membranes were used as both electrode materials and basic separation system. With −5 V electric field being applied, 57.6% of reduction in water flux loss was observed, while microalgae recovery efficiency increased by 17.3%. The lipid content also increased to nearly 38%. Meanwhile, the inevitable reverse diffusion of solutes in the FO process and the concentration process of the microalgae solution increased the salinity of the microalgae solution, which is generally regarded as an obstacle for the application of FO. However, in the electrically-assisted FO system, it not only improved the efficiency of the electrochemical process, but also can increase the lipid content. The lipid extraction efficiency of the −5 V electric field increased from 17.7% and 28.5% to 20.4% and 31.1%, respectively, with one and two times extractions. The synergistic effect of the reverse diffusion of Cl− and electrochemical process was conducive for the improvement of the lipid extraction efficiency, and is expected to reduce the energy consumption of the lipid extraction process.