Oil production by six microalgae: impact of flocculants and drying on oil recovery from the biomass

Oil production in batch photoautotrophic cultures of the following microalgae is reported: the freshwater microalgae Chlorella vulgaris, Choricystis minor, and Neochloris sp.; the marine microalgae Nannochloropsis salina and Cylindrotheca fusiformis; and C. vulgaris grown in a full-strength seawater medium. In all cases, the solvent extraction of lipids from freeze-dried biomass is compared with extraction from the fresh biomass paste. For all algae, the oils could be extracted equally effectively from freeze-dried samples and the paste samples (67–88 % moisture by weight). Moisture content determinations of the biomass using the freeze-drying method and the high-temperature oven drying were found to be equivalent for all algae. The biomass recovered by flocculation with metal salts (aluminum sulfate, ferric chloride) followed by centrifugation had a certain amount of the flocculant irreversibly bound to it. Washing failed to remove the adsorbed flocculants. For all algae, the adsorbed flocculants did not interfere with oil recovery by solvent extraction. The solvent system of chloroform–methanol–water proved highly effective for quantitative extraction of the lipids from all algae.