3-44: Optimal coagulant doses to promote elevated biomass recovery efficiency

Because of the world energy crisis, global warming and restrict feedstock availability, alternative liquid  fuels  to petro fuel must be developed. Among the huge list of potential feedstocks for biofuel production, experts agree that a future overall approach would adopt an algal-based biorefinery model to convert biomass in biofuel (biodiesel, bioethanol, biogas and biohydrogen). However, a major challenge to scale up algal-based fuels is the improvement of the processes to harvest cells, which would increase the commercial potential  of those. Harvesting microalgae can be difficult and costly, because of their small cell size and their low concentration. The choice of harvesting technique depends mainly on the characteristics of the microorganism and occurs in two stages process. In this research, flocculation followed by gravitational sedimentation was evaluated to promote the Chlorella vulgaris harvesting. Different dosages of organic coagulant and Al₂(SO₄)₃ were tested in a wide range of biomass concentrations and pHs to maximize the biomass recovery efficiency (RE).  The results showed that is possible to use pHs between 4-11 with the organic coagulant and between 7-8 with Al₂(SO₄)₃ obtaining more than 98% of RE with 0,08g_{org_coag}/g_biomass and 0,40g_Al2(SO4)3/g_biomass. Also, it was observed that organic flocculants are generally more effective, because can absorb several particles at once, forming a three-dimensional matrix that are easier to harvest. Finally, the use of low amounts of organic coagulant to promote biomass harvesting in a wide range of pH and with elevated RE is economically feasible. Acknowledgements: PETROBRAS, FAPESP, CAPES and CNPQ.