Creating circular pathways for nutrients in aquaculture using biochar

Global food production drives planetary-boundary transgressions, including nitrogen and phosphorus cycle disruption, land use change, and climate change. Increasing nutrient circularity can improve sustainability. This study explores an integrated approach that combines a recirculating aquaculture system (RAS) with biochar from forestry-residue pyrolysis to improve process-level nutrient retention while producing carbon-rich biochar with potential for soil-carbon storage upon land application. In RAS, biochar acts as a filter, capturing nutrients and transforming waste into nutrient-enriched biochar for agriculture. Substance Flow Analysis shows that integration increases nitrogen retention from 30.6 % to 44.6 % and phosphorus retention from 25.5 % to 99.6 % versus separate RAS and pyrolysis. This demonstrates the potential of linking aquaculture, forestry, and agriculture with biochar to support more circular and sustainable food production. This early-stage study examines how and to what extent the approach influences nutrient flows under different assumptions and evaluates a simple recovery-efficiency indicator for assessing circularity in integrated systems.