BACKGROUND Given the small size of microalgae, and the low biomass concentrations obtained in light-limited cultures, the cost of algae harvesting is a significant barrier to commercial-scale production of biofuel from algae. A downward- flow inclined gravity settler was evaluated for its effectiveness in dewatering the microalgae Scenedesmus dimorphus and Chlorella vulgaris. RESULTS Experimental results showed that S. dimorphus can be concentrated up to 8-fold using a single settler stage, with a biomass recovery of 80%. Separation efficiency was independent of biomass concentration between 1 and 5 gdw L-1, suggesting that a two-stage sequential system of settlers may maximize biomass recovery and concentration effectively. Efficiency of separation of C. vulgaris was slightly lower than that of S. dimorphus, most likely due to the fact that S. dimorphus exist in aggregates of four or more cells and thus may settle more easily. CONCLUSION The downward-flow inclined gravity settler demonstrated consistent results with 72% efficiency in biomass recovery and low operating costs. This separation system warrants further investigation at the industrial scale, for the harvesting of algae from dilute cell suspensions, with applications to biofuels. (c) 2013 Society of Chemical Industry