Algal cells harvesting using cost-effective magnetic nano-particles.

Innovative iron-based nanoparticles were synthesized, characterized and tested for the first time for harvesting single and mixed algal culture from real wastewater. The tailor-made magnetic nanoparticles (MNPs; Fe-MNP-I and Fe-MNP-II) achieved a percentage algae harvesting efficiency (%AHE) higher than 95% using a concentration of MNPs (C) of 25 ± 0.3 (std. dev = 0.08) mg.L, mixing speed (M) of 120 ± 2 (std. dev = 0.10) rpm, short contact time (C) of 7 ± 0.1 (std. dev = 0.05) min and separation time (SP) of 3 ± 0.1 (std. dev = 0.09) min. The optimum operational conditions for harvesting of Chlorella vulgaris (C.v) were determined at (C = 40 ± 0.4 (std. dev = 0.5) g.L, SP = 2.5 ± 0.4 (std. dev = 0.1) min, M = 145 ± 3 (std. dev = 1.50) rpm and C = 5 ± 0.3 (std. dev = 0.10) min using surface response methodology. Langmuir model describes better the adsorption behavior of algae-Fe-MNP-I system, while both Langmuir and Freundlich fit well the adsorption behavior of algae-Fe-MNP-II. The maximum adsorption capacity of Spirulina platensis (SP.PL) (18.27 ± 0.07 (std. dev = 0.19) mg.mg) was higher than that for Chlorella vulgaris (C.v) (11.52 ± 0.01 (std. dev = 0.34) mg.mg) and mixed algal culture (M.X) (17.20 ± 0.07 (std. dev = 0.54) mg.mg) over Fe-MNP-I. Zeta potential measurements revealed that the adsorption mechanism between MNPs and algal strains is controlled by electrostatic interaction. The synthesized MNPs were recycled 10 times using alkaline-ultrasonic regeneration procedure.