A novel method to recover microalgae by compound buoyant-bead flotation

To improve the recovery efficiency of buoyant-bead flotation (BBF), a novel compound buoyant-bead flotation technology (CBBF) using acidified fly ash cenospheres with heat-aided pre-flocculation was developed. The effects of cenospheres concentration (0.6–3 g L−1), flotation time (5–20 min) and pH values (2–10) were studied. Response Surface Methodology was utilized to optimize the CBBF process. The results showed that pH value had the greatest influence on the recovery process. When pH values were low, the Chlorella vulgaris (C. vulgaris) cells began to flocculate, which helped to form the “C. vulgaris-cenosphere” aggregates and improved the recovery efficiency. To avoid the addition of flocculants, heat-aided pretreatment was used to promote flocculation process. The maximum recovery efficiency (93.04 ± 0.60%) was obtained at cenospheres concentration of 2.83 g L−1, pH value of 2.41, flotation time of 17.05 mins and flotation temperature of 90 °C. Furthermore, it was demonstrated that this CBBF method can be also widely applied to other microalgae strains, such as Scenedesmus obliquus, Spirulina platensis, Microcystis aeruginosa and Anabaena variabilis. It can be concluded that the CBBF technology is a feasible and highly efficient (over than 90%) process for the removal of various microalgae.