Microalgae have the potential to be the feedstock for biofuels and laboratory scale electroflocculation was studied as a harvesting technique for marine microalgae. The effects of the electrode separation and mechanical mixing on the energy consumption were also assessed. Results were used to design a commercial scale electroflocculation plant for the estimation of the harvesting cost. By combining electroflocculation with mixing and settling, an overall energy consumption of 0.33 MJ In-3 has been achieved. On a large scale, the mixing can be made energy efficient by the use of a baffled hydraulic mixer. The total cost for the harvesting, including electrical energy, electrode metal dissolution and capital depreciation, is estimated to be $0.19 kg(-1) of the ash free dry mass. Hence, electroflocculation has the potential to be more economical than other harvesting techniques for marine microalgae. (C) 2013 Elsevier Ltd. All rights reserved.