Comparative life-cycle assessment of microalgal biodiesel production via various emerging wet scenarios: Energy conversion characteristics and environmental impacts

Abstract

Various scenarios for biodiesel production from wet microalgae were recently reported to eliminate the energy consumption of microalgae drying. However, the comparative investigations on the environmental impacts and energy consumption of those scenarios were limited. In present study, four emerging scenarios (LE-PEF, IST-EAC, IST-MAT and LE-MHT) using different strategies and different solvents were analyzed and compared in term of net energy ratio (NER), greenhouse gas (GHG) emissions, ecotoxicity, and human toxicity. The results show that although the energy consumption of microalgae drying is eliminated, new energy consumption and environmental impacts were arising as solvent usage increased. The LCA results revealed that the solvent used during biodiesel production was the dominant contributor to the environmental impacts and energy consumption. The best NER (0.73), GHG emissions (−41.12 g CO2-eq MJ−1), human toxicity (2.15E-14 case MJ−1), and ecotoxicity (2.4E-4 PAF m3 d MJ−1) was observed in LE-MHT, mainly ascribed to the minimal usage of organic solvent. LE-PEF resulted in the worst environmental impact, owing to its over usage of chloroform, which is characterized by high global warming potential and high toxicity. Due to the extensive usage of solvent during in-situ transesterification, high NERs were reported for both IST-MAT and IST-EAC. The comparison between IST-MAT and IST-EAC demonstrated that the human toxicity was significantly decreased when hexane was replaced by ethyl acetate. The energy conversion characteristics and environmental performance could be further improved by minimizing solvent usage, using eco-friendly solvents, and increasing lipid recovery.