Life-cycle assessment of biofuel production from microalgae via various bioenergy conversion systems

Microalgae is an alternative feedstock for biofuel production and has been considered to be a potential biotechnology. However, the systems for industrial biofuel production from microalgae are still costly and unsuitable. In addition, the complex and changeable processes contained in different bioenergy conversion systems make it difficult to reasonably compare these systems. This study aim to obtain an optimal microalgae-based industrial system using life-cycle assessment, and to unify the uncertainties caused by the discrepancies of each process. Two types of bioenergy conversion systems were modelled and compared: (1) transesterification, hydrothermal liquefaction, and pyrolysis for renewable diesel production and (2) anaerobic digestion without/with hydrothermal pretreatment for biogas production. The life-cycle impacts of these systems were quantified in terms of net energy ratios (NERs) and greenhouse gas (GHG) emissions. The results show that anaerobic digestion system with hydrothermal pretreatment is more industrially feasible and eco-friendly at the industrial scale due to its low NER (0.71) and GHG emissions [-60.84 g CO2-eq (MJ biogas)(-1)]. (C) 2019 Elsevier Ltd. All rights reserved.