Magnetophoretic removal of microalgae from fishpond water: Feasibility of high gradient and low gradient magnetic separation

Microalgae blooms in commercial fish production ponds resulting in a deficit in the overall oxygen budget have posed serious challenges to aquaculture industry. In this study, we demonstrate the feasibility of rapid microalgae separation in real-time from fishpond water by magnetophoresis. By relying on the magneto-shape anisotropy of rod-liked iron oxide magnetic nanoparticle (IONPs), overall separation efficiency of microalgae cells up to 90% can be achieved in less than 3 min. The IONPs employed, with a saturation magnetization at 113.8 emu/g, are surface functionalized with cationic polyelectrolyte that promotes the attachment of these particles onto microalgae cells via electrostatic interaction. Kinetic of magnetophoretic separation process was monitored by suspension opacity measurements based upon a custom built light dependent resistor (LDR setup) sensor. Whereas, the overall separation efficiency of microalgae cells is determined spectrophotometrically at 685 nm wavelength. Performance of both high gradient magnetic separation (HGMS) with ∇B > 1000 T/m and low gradient magnetic separation (LGMS) with ∇B < 80 T/m were tested with varying particle concentration (50–500 mg/l) and the results obtained were interpreted in term of cooperative magnetophoresis theory. Cost analysis was conducted to verify the feasibility for large scale implementation of LGMS system with the cost involved at $0.13 for every one meter cube of treated fishpond water.

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► Rapid magnetophoretic separation of mixed strains of microalgae from fishpond water is feasible.
► The concentration of surface functionalized IONPs affect the microalgae removal efficiency.
► LGMS and HGMS systems achieve high separation efficiency.
► Kinetic behavior of both LGMS and HGMS systems are compared.
► LGMS system more cost effective for small scale fishfarm water treatment.