Assessing the environmental footprint of microalgae biofuel production: A comparative analysis of cultivation and harvesting scenarios

This study investigated the impact of fixed combinations of three flocculants and four buoy-beads under two cultivation systems on the harvesting efficiency, as well as the environmental performance in different scenarios. Results showed that the harvesting efficiency exhibited a tendency of initially increasing and then decreasing with rising concentrations of buoy-beads and flocculants, with an optimal harvesting efficiency of 98.03 %. Life cycle assessment (LCA) compared the environmental performance of five scenarios. Ecotoxicity Soil Chronic (ESC) and Aquatic Eutrophication EP(P) (AEP(P)) were major environmental impacts. The scenario employing re-frying oil emulsion (RFOE) and aluminum sulfate flocculation (R+A) contributed significantly to Human Toxicity Water (HTW) and Aquatic Eutrophication EP(N) (AEP(N)) with normalized values of 0.0137 and 0.0147, respectively. In the assessment of Global Warming Potential (GWP), R+A was responsible for a high amount of Greenhouse Gas (GHG) emissions (2.826 kg CO2 eq/100 g of dry algal biomass in photobioreactor (PBR) and 2.917 kg CO2 eq/ 100 g of dry algal biomass in open raceway ponds (ORP)). Notably, sodium alginate microspheres (SAMs) and aluminum sulfate flocculation (S+A) was considered a more environmentally favorable option, 0.773 kg CO2 eq and 0.864 kg CO2 eq GHG emissions of PBR and ORP, respectively. Furthermore, the less GHG emissions of PBR than ORP, making it a more effective solution for reducing emissions and mitigating global warming trends.