A simple and rapid harvesting method for microalgae by in situ magnetic separation

A simple and rapid harvesting method by in situ magnetic separation with naked Fe3O4 nanoparticles has been developed for the microalgal recovery of Botryococcus braunii and Chlorella ellipsoidea. After adding the magnetic particles to the microalgal culture broth, the microalgal cells were adsorbed and then separated by an external magnetic field. The maximal recovery efficiency reached more than 98% for both microalgae at a stirring speed of 120 r/min within 1 min, and the maximal adsorption capacity of these Fe3O4 nanoparticles reached 55.9 mg-dry biomass/mg-particles for B. braunii and 5.83 mg-dry biomass/mg-particles for C. ellipsoidea. Appropriate pH value and high nanoparticle dose were favorable to the microalgae recovery, and the adsorption mechanism between the naked Fe3O4 nanoparticles and the microalgal cells was mainly due to the electrostatic attraction. The developed in situ magnetic separation technology provides a great potential for saving time and energy associated with improving microalgal harvesting.