Optimization of chemical flocculation of Scenedesmus obliquus grown on municipal wastewater for improved biodiesel recovery

Cost-efficient harvesting of microalgae is a major challenge for large-scale biomass production. The present study aimed to optimize and model the flocculation process for efficient harvest of the biodiesel promising green microalga Scenedesmus obliquus grown in municipal wastewater. In addition, the influence of applied flocculation on biodiesel recovery was measured. Ferric sulphate showed the highest relative flocculation efficiency in comparison with the other tested flocculants. At initial OD680 of 1, the flocculent dose required to achieve 99.5% flocculation efficiency was 150 mg L-1 after 40 min. In addition, relatively higher flocculation efficiencies of S. obliquus cells were observed at lower initial OD680. The suggested polynomial model showed satisfactory and accurate results, with high positive correlation (0.956) between the calculated and measured flocculation efficiency. Furthermore, fatty acid methyl esters (FAMEs) yield of the flocculated biomass showed 40.9% significant increase (P < 0.01) over the centrifuged cells. It can be concluded that flocculation using ferric sulphate is greatly advantageous, as in a single step it served a dual propose of algal biomass harvest and enhanced FAMEs recovery at doses much lower than that used in wastewater treatment plants. (C) 2017 Elsevier Ltd. All rights reserved.