Using magnetic materials to harvest microalgal biomass: evaluation of harvesting and detachment efficiency

Using naked iron oxide (Fe₃O₄) and yttrium iron oxide (Y₃Fe₅O₁₂) nanoparticles as flocculants, the harvesting efficiency of Chlorella vulgaris biomass was investigated. The harvesting process includes two steps, which are the separation of microalgae from the culture solution with the magnetic nanoparticles and then the separation of the algae from the magnetic nanoparticles. The optimal dosages and pH values for the magnetic harvesting of microalgal biomass were determined. Results showed that Y₃Fe₅O₁₂ nanoparticles were more efficient in microalgal biomass harvesting than Fe₃O₄ nanoparticles. In an effort to achieve more than 90% of harvesting efficiency, optimal dosages for Fe₃O₄ and Y₃Fe₅O₁₂ to harvest microalgal biomass were 10 and 2.5 g/L, while the appropriate pH values were 6.2 and 7.3, respectively. The harvesting efficiency of Fe₃O₄ and Y₃Fe₅O₁₂ nanoparticles increased as the pH value decreased. The experimental results also showed that under a higher pH value Fe₃O₄ nanoparticles were much easier to be separated from the flocs than Y₃Fe₅O₁₂. 62.9% of Fe₃O₄ nanoparticles could be de-attached from the aggregates, when the floc pH value reached 12.3.