Identifying Life Cycle Environmental Hotspots in Phosphorus Recovery from Wastewater Using Modified Biochars

Biochar offers a potential sustainable pathway for recovering phosphorus from wastewater to agriculture. Magnesium-modified biochar has demonstrated an enhanced phosphate adsorption capacity and excellent bioavailability. This study aims to identify the life cycle environmental hotspots in phosphorus recovery from wastewater using magnesium-modified biochars derived from bamboo, corn, and wood and compared them with common phosphate fertilizers. The results show that the biomass supply stage and the modification stage are the main environmental hotspots in most impact categories. As the phosphorus load of wastewater decreases, the phosphorus recovery stage could become the hotspot. Although phosphate-loaded magnesium-modified biochars in the base case do not have a better overall environmental performance than most phosphate fertilizers (especially those without nitrogen), they have significantly lower mineral resource scarcity and ecotoxicity. The sensitivity analysis suggests that the results are sensitive to the background inventory selected. The analysis indicates that the biochar yield, the phosphate adsorption capacity of the biochars, the source of modification chemical, and the source of biomass feedstock are key areas for technological and inventory improvement. In the future, a comprehensive field application inventory and a diverse set of background inventory are needed to better assess this sorption-based phosphorus recovery pathway.