2.5.1. Magnetic Harvesting Experimental Procedure

The magnetic harvesting experiments of C. vulgaris biomass were carried out under ambient conditions in batch mode. The experimental procedure included the following steps: (a) The pH of the microalgal cultivation was fixed at the desired value through the addition of aqueous NaOH or HCl solutions, (b) in order to facilitate the flocculation between the algal cells and the particles, 10 mL of the microalgae cultivation was mixed with a given amount of magnetic particles for 10 min using a mechanical stirrer operating at desired rpm, and (c) the flocs were separated from the cultivation medium with the application of a strong magnetic field, imposed using the same permanent magnet which was employed during the synthesis of the magnetite particles, for 3 min.

Finally, the harvesting efficiency (HE%) of the process was calculated from Equation (1):

where, OD₀ is the initial absorbance of the microalgae cultivation at a wavelength of 600 nm, and OD₁ is the absorbance at the same wavelength of the supernatant liquid that separates from the microalgae-particles flocs after the application of the magnetic field. The OD₀ and OD₁ values were measured with the UV-VIS S-22 BOECO spectrophotometer.