A mechanistic mathematical model was developed to predict the performance of cationic polymers for flocculating salt water cultivated microalgae. The model was validated on experiments carried out with Neochloris oleoabundans and three different commercial flocculants (Zetag 7557 (R), Synthofloc 5080H (R) and SNF H536 (R)). For a wide range of biomass concentrations (0.49-1.37 g L-1) and flocculant dosages (0150 mg L-1) the model simulations predicted well the optimal flocculant-to-biomass ratio between 43 and 109 mg(flocculant/gbiomass). At optimum conditions biomass recoveries varied between 88% and 99%. The cost of the usage of commercial available flocculants is estimated to range between 0.15 $/kg(biomass) and 0.49 $/kg(biomass). (C) 2015 Elsevier Ltd. All rights reserved.