Ratio between autoflocculating and target microalgae affects the energy-efficient harvesting by bio-flocculation

► Bio-flocculation is a promising pre-concentration step for harvesting microalgae. ► Bio-flocculation reduces the energy for harvesting to at least 1.83 MJ kgDW−1. ► The ratio autoflocculating to target microalgae increases the recovery. ► Sedimentation rate increases with ratio autoflocculating to target microalgae.