Environmental assessment of the valorization of glycerol for the production of hyperthermophilic β-glucosidase under a biorefinery approach

Bioethanol production technologies from lignocellulosic biomass are not yet optimized and do not compete economically with first-generation bioethanol production. Strategies have been investigated to produce more active, stable and temperature-tolerant enzymes to be used for biomass hydrolysis such as the hyperthermophilic β-glucosidase produced by Yarrowia lipolytica. The use of this strain offers an additional competitive advantage, as it can use glycerol stream from the biodiesel process as a carbon source. In this way, not only is a by-product of biofuel production used, but the enzyme could be applied in the production of lignocellulosic ethanol, increasing the value chain by closing the bioeconomy cycle. To this end, large-scale process modelling of β-glucosidase production has been developed to collect the inventory data needed for life cycle assessment methodology. The fermentation stage is the largest contributor to environmental impacts, with electricity being the main hotspot identified, contributing more than 50% in most impact categories. Residual glycerol has also been identified as a critical input, with a significant contribution in some categories. To improve the environmental profile, a sensitivity analysis has been carried out considering reductions in electricity and heat consumption, and other alternative oil-based resources for the production of biodiesel. This analysis identified that large environmental reductions could be achieved, which makes the valorization of the glycerol obtained as a side stream of biodiesel production more realistic.This research has been supported by the project Enhancing diversity in Mediterranean cereal farming systems (CerealMed) project funded by PRIMA Programme and FEDER/Ministry of Science and Innovation-Spanish National Research Agency (PCI 2020-111978) and by a project granted by Xunta de Galicia (project ref. ED431 F2016/001). The authors belong to the Galician Competitive Research Group (GRC ED431C 2017/29) and to the Cross-disciplinary Research in Environmental Technologies (CRETUS Research Center, ED431E 2018/01)S