Acidified-flocculation process for harvesting of microalgae: Coagulant reutilization and metal-free-microalgae recovery

Chemical flocculation is considered to be an overall low-cost and up-scalable process for harvesting of microalgae. In this study a new flocculation approach utilizing metal coagulant (Fe2(SO4)3) and sulfuric acid (H2SO4) was introduced for harvesting of Chlorella sp. KR-1, which overcome two main issues of contamination and reuse of coagulant. Reduction of pH successfully released precipitates attached to the microalgae, and the remaining acidic solution containing recovered ferric ions could be reused for harvesting up to three times with high, better-than 98% efficiencies. Moreover, the acid-treated microalgal biomass could be directly used for lipid extraction without additional catalyst. High extraction yields of around 32% were achieved with FAME conversion efficiencies of around 90%. The integrated approach devised in the present study is expected to make the best use of the age-old yet effective harvesting means of flocculation, which can be a practical and economical option in microalgal biorefinery.