Biogenic magnetite nanoparticles for the magnetic separation of microalgae

The biotechnological potential of microalgae is significant in various industrial sectors, but inefficient and expensive harvesting techniques hinder its widespread use. Regarding cell separation and concentration, few works used magnetic materials to harvest the cells. In general, the interaction between the mineral particles and cells is greatly influenced by pH and salinity conditions, which can limit their range of applications. Biogenic magnetite nanoparticles (BMs) produced by magnetotactic bacteria have unique magnetic properties and surface chemistry that can be applied for microalgae harvesting. In our experimental procedure, it was defined that 80 μg BMs·mL⁻¹ under a more acidic pH was ideal for the process with cell density ranging from 3·10³ to 1,2·10⁴ cells/mL. At pH 3.1, it was possible to magnetically concentrate up to 80.08 ± 2.08 % and 75.26 ± 2.45 % of Scenedesmus sp. and Desmodesmus sp. biomass, respectively. BMs also showed a reasonable recovery rate (52.08 %) when challenged under hypersaline conditions (40 g NaCl·L⁻¹) at pH 3.1 for Nannochloropsis sp. In this condition, synthetic magnetite nanoparticles (SMPs) and flocculants are ineffective in biomass harvesting. Thus, this work describes the process and efficiency of a magnetic nanotool capable of magnetically concentrating microalgae for downstream applications.