On how to make aquaponics more circular

Aquaponics is a recognised food system for its circular nutrient management potentiality, as it redirects aquaculture waste into plant production. However, current practices still fall short of closing nutrient loops, with substantial losses occurring through dissolved effluents and solid waste. This review examines strategies to reduce losses, recover nutrients, internally recycle dissolved streams, and valorise solid side streams in aquaponics, with particular attention to nitrogen and phosphorus due to their dual role as essential, and often limiting, inputs in aquaculture and plant production as well as key pollutants with major eutrophication potential. First, we identify the fate of dissolved and solid nutrients from both aquaculture and hydroponic subsystems. Second, we evaluate strategies to recover these nutrients, exploring opportunities to recycle dissolved nutrients and water, reuse solid waste, and reduce system-wide impacts. Third, we discuss the importance of integrating these processes at a system level and reflect on how current innovations can be better aligned with circular bioeconomy principles. Our synthesis concluded that while the integration of these strategies into optimally efficient, circular aquaponic systems is an ongoing challenge, several key nutrient recovery technologies are themselves well-established and have been successfully implemented. Addressing the gap in knowledge and industry practice will require systems thinking, deeper cross-disciplinary collaboration, and applied research that goes beyond isolated interventions.