Climate dependent feasibility of closing water and nutrient cycles in industrial aqua-agriculture

In integrated aqua-agriculture, matching waste-derived nutrient supply with crop demand while maintaining optimal fish and crop conditions remains challenging. We formulate a closed-loop aquaculture-hydroponics network with anaerobic digestion as a constrained optimal-control problem and combine static sizing with climate-driven dynamic flow optimization for contrasting climates. Under weak seasonality (Jakarta), internal wastes (aquaculture water, fish sludge, and plant residues) support discharge-free operation with water, nitrogen, and phosphorus use-efficiencies of 100%, 79%, and 72%. As seasonality increases (Cairo, Amsterdam), feasibility and robustness decline due to shifting demand and limited phosphorus recoverability. Using manure as co-digestion substrate restores closed-cycle operation without synthetic fertilizers. The optimizer prefers pig manure in Cairo and chicken manure in Amsterdam, reflecting climate-specific N:P deficits. Relative to climate-matched decoupled aquaponics, optimized integrated networks cut water, nitrogen, and phosphorus waste by 86%, 46%, and 35%. Overall, the framework enables climate-robust design of circular aqua-agriculture networks, reducing resource use and pollution.