Researchers from Institute of Process Engineering, Chinese Academy of Sciences (IPE) have developed a simple and rapid method by in situ magnetic separation with Fe₃O₄ nanoparticles to improve microalgae harvesting.

Microalgae are good resources for biofuel production and have great potential in application of biological fields because of their dilute nature. Microalgae harvesting is a significant factor in wastewater recycling and environmental management. Several separation methods for microalgae recovery have been reported including centrifugation, filtration, flocculation and flotation.

In situ magnetic separation is an economic and efficient method for biomolecules separation from liquid solution. Using Fe₃O₄ nanoparticles as the magnetic particles, the recovery efficiency of Botryococcus braunii and Chlorella ellipsoidea reached above 98% within 1min on the condition of an external magnetic field.

Magnetic nanoparticles with an average diameter of 10nm were synthesized by a chemical precipitation method. Effects of stirring speed, pH and nanoparticle dose on recovery efficiency (RE) were discussed. When increased stirring speed from 40rpm to 120rpm, the microalgae RE improved. However, further increase of stirring speed over 120rpm did not improve RE further. Low pH was good for harvesting cells of B. braunii and RE of C. ellipsoidea reached highest at pH 7.0. RE increased as more nanoparticles used. The results showed that adsorption isotherms of both cells on magnetic particles were fitted with Langmuir model well. The electrostatic attraction between the magnetic nanoparticles and microalgal cell was the mainly reason for adsorption mechanism.

The research paper "A simple and rapid harvesting method for microalgae by in situ magnetic separation"  has been published on Bioresource Technology.