From poor quality soil to valuable biofuels: Sustainability assessment of phytoremediation-based soil decontamination integrated with biofuel production

Phytoremediation has the potential of becoming a sustainable method of restoring contaminated soil to agricultural use, especially if the harvested biomass is valorised by production of biofuels. In the Phy2Climate research project, phytoremediation of sites contaminated with heavy metals and hydrocarbons was combined with innovative biomass processing technologies to produce clean biofuels and bio-coke. Sustainability of the investigated technology was determined by performing a Life Cycle Assessment (LCA). In total, 3 cases of phytoremediation were investigated (differing in the type of contamination and used plant species), together with 3 variants of biorefinery configuration. Inventory data collected from the project partners, literature reviews and own mathematical modelling were fed into a model prepared in LCA for Experts software. Special focus was put on taking into account the amount of removed contaminants. The LCA revealed favourable environmental impacts, with most indicators scoring negative values (expressing avoided burdens). Most negative impacts of the processing chain are offset by the avoided use of fossil fuels, especially coke. Impacts in toxicity-related categories are also favourable, although ultimately they will be strongly case-specific and dependent on the type of the removed contamination. As an additional sustainability metric, thermo-ecological cost (TEC) of the biorefinery products was calculated. TEC expresses the cumulative consumption of non-renewable exergy of natural resources burdening all stages of fabrication of a given product. For all investigated variants, the values of TEC are lower than 1 J of non-renewable exergy per 1 J of biorefinery products, which highlights the sustainability of these biofuels.