Environmental sustainability of a biochar integrated nature-based solution in Finland: A comparative LCA with a rain garden and a sand filter

Biochar based stormwater filters are gaining popularity worldwide due to their high effectiveness in removing pollutants. However, the comprehensive evaluation of the environmental impacts of these novel approaches is limited, leaving an unclear picture of their overall environmental sustainability. This study aims to address this gap by conducting a comparative, cradle-to-grave life cycle assessment (LCA) to evaluate a biochar integrated nature-based solution (NBS) implemented in Finland. The analysis includes comparisons with two hypothetical systems: a rain garden (RG) and a sand filter (SF), along with a baseline (BL) scenario representing no-treatment. When comparing the impacts of treatment systems with the BL, a clear burden shift can be identified among the eleven impact categories evaluated in this study. The treatment systems offer water treatment benefits during the operational phase across the categories of freshwater and marine eutrophication, freshwater and marine ecotoxicity, and human toxicity (non-cancer). While NBS and RG provide the most significant water treatment benefits compared to SF, they also cause the most substantial infrastructure-related impacts. In contrast, SF demonstrates up to 90% lower impacts across categories, including global warming, human toxicity (cancer), terrestrial acidification and ecotoxicity, fossil depletion, and land use. In all treatment systems, the construction phase contributes the most to life-cycle impacts (50–100%) in these categories. The results further show that stormwater-specific impacts are highly sensitive to influent concentrations and treatment performance, highlighting the importance of considering site-specific water quality data when evaluating the benefits of water treatment.