Harvesting fresh water and marine algae by magnetic separation: Screening of separation parameters and high gradient magnetic filtration

[Display omitted] ► Magnetic separation for efficient harvesting of fresh water and marine algae. ► High separation efficiencies >95% can be obtained. ► Fumed silica-coated magnetite as alternative to precipitated magnetite. ► Separation efficiency depends on particle concentration, pH and medium composition. ► Scalability is possible by means of high gradient magnetic filtration. In this study, the focus is on magnetic separation of fresh water algae Chlamydomonas reinhardtii and Chlorella vulgaris as well as marine algae Phaeodactylum tricornutum and Nannochloropsis salina by means of silica-coated magnetic particles. Due to their small size and low biomass concentrations, harvesting algae by conventional methods is often inefficient and cost-consuming. Magnetic separation is a powerful tool to capture algae by adsorption to submicron-sized magnetic particles. Hereby, separation efficiency depends on parameters such as particle concentration, pH and medium composition. Separation efficiencies of >95% were obtained for all algae while maximum particle loads of 30 and 77g/g were measured for C. reinhardtii and P. tricornutum at pH 8 and 12, respectively. This study highlights the potential of silica-coated magnetic particles for the removal of fresh water and marine algae by high gradient magnetic filtration and provides critical discussion on future improvements.