Magnetophoretic separation of Chlorella sp.: Role of cationic polymer binder

•The electrostatic attraction initiates the effective attachment of magnetic nanoparticles onto microalgal cell surface.•The cationic polymer binders enable the electrostatic-mediated-attachment of SF-IONPs on cell surface that eventually promote up to 99% of cell separation efficiency.•PDDA is more preferable as binder than the ChiL because of their pH dependency.•Polymer binder has modified the surface property of the magnetic nanoparticles but maintains its magnetic responsive in core. Cationic polyelectrolyte promoted effective attachment of iron oxide nanoparticles (IONPs) onto microalgal cells through electrostatic attraction. Poly(diallyldimethylammonium chloride) (PDDA) and chitosan (ChiL), both are cationic polymer, are feasible to act as binding agent to promote rapid magnetophoretic separation of Chlorella sp. through low gradient magnetic separation (LGMS) with field gradient ▿B less than 80T/m in real time. Cell separation efficiency up to 98% for the case of PDDA and 99% for the case of ChiL can be achieved in 6min when 3×107cells/mL Chlorella sp. are exposed to 300mg/L surface functionalized-IONPs (SF-IONPs). Different polyelectrolytes do not give significant effect on cell separation efficiency as long as the particle attachment occurred. However, the PDDA is more preferable as the binder for all type of microalgae medium than the chitosan (ChiL) since it is not pH dependent. SF-IONPs coated with PDDA guarantee the cell separation performance for all pH range of cell medium, with 98.21±0.40% at pH 8.84. On the other hand, the ChiL performance will be affected by the cell medium pH, with only 22.93±31.03% biomass recovery at pH 9.25.