Effect of improvement actions on the life-cycle environmental and economic performance of synthetic biofuels from date palm waste in Tunisia

The use of biowaste to produce synthetic fuels is often proposed to overcome sustainability issues associated with conventional fossil fuels. Several routes and processes from waste feedstock to final fuels have proven to be technically feasible, whereas economic and environmental aspects typically differ from one system to another depending on the specific conditions and context. In a previous study on the life-cycle sustainability performance of synthetic diesel and gasoline from Tunisian date palm waste, critical concerns on the use of grid electricity and conventional oxygen were reported. In order to further explore the potential environmental and economic suitability of this biofuel production pathway, this article revisits and extends the former case study by assessing the effect of implementing renewable electricity and alternative oxygen. In particular, the use of photovoltaics (PV) to provide electricity to the synthetic fuel plant, as well as its use in local oxygen production, is considered. System Advisor Model (SAM) software is used to simulate a PV plant, including the estimation of the levelised cost of energy. Life Cycle Assessment (LCA) and Life Cycle Costing (LCC) are applied to estimate the environmental and economic life-cycle profile of the synthetic biofuels when the potential improvement actions are implemented. When compared to the original system, a slight decrease in total production costs is found, yet considering higher capital costs related to PV installation. Regarding the environmental dimension, findings on the suitability of the alternative system depend on the specific impact category and the reference target, with significant potential savings (e.g. climate change) but also greater potential impacts (e.g. use of minerals and metals) when benchmarked against both the original bioenergy system and conventional fossil fuels. This evinces complex decision-making when multiple sustainability aspects are taken into account, but suggesting the suitability of the proposed measures if the long-term benefits of climate change mitigation and the current national decarbonisation targets are prioritised.