Aquaculture systems generate nutrient-rich effluents containing high loads of nitrogen, phosphorus, and organic matter, which can cause serious environmental harm if not properly treated. As a result, farmers are compelled to invest significant resources in waste management. Transforming these "wastes" into resources is a central challenge for sustainable aquaculture. Aquaponics—an integrated system that combines aquaculture with hydroponics—offers a promising solution by enabling the recovery and reuse of water, nutrients, and organic compounds. However, traditional one-loop aquaponics systems utilize only a fraction of the available nutrients, particularly those locked in solid waste (sludge). These systems are also limited by the tight coupling between the fish and plant units, which restricts the ability to optimize conditions independently and reduces system flexibility. Any malfunction in one component can negatively impact the entire system, compromising stability and performance.
This study presents a novel, zero-waste multi-loop aquaponics configuration designed to overcome the limitations of conventional one-loop systems. Our system integrates three independently optimized subsystems: (1) a recirculating aquaculture system (RAS), (2) deep-water hydroponics, and (3) anaerobic digestion units—one for fish sludge and another for plant residues. These digesters maximize nutrient mobilization and recovery. The system was deployed in a desert environment and operated under near-zero discharge conditions. Anaerobic supernatants were returned to the hydroponic loop as a nutrient-rich solution, while biogas was harvested as a renewable energy source.
Compared to traditional decoupled and coupled systems, the novel multi-loop system showed substantial improvements in resource recovery and overall productivity. Nutrient recovery rates for nitrogen and phosphorus reached 76% and 80%, respectively—up to twice the efficiency of standard one-loop designs. Plant productivity increased significantly, reaching 11.8 kg of lettuce per kg of fish feed, representing a 1.6-fold improvement over conventional systems. Furthermore, the system used 2.1× less water and required 16% less energy per kg of feed, with biogas production offsetting 84% of energy demand. Photosynthetic CO₂ sequestration further contributed to reducing the system’s carbon footprint.
In summary, multi-loop aquaponics with integrated anaerobic digestion offers a scalable, circular, and resilient model for sustainable food production. By decoupling biological flows through engineered loops, this approach maximizes nutrient use, minimizes waste, enhances crop yields, and recovers may energy. These findings highlight its strong potential for sustainable agriculture in arid and urban settings where traditional farming methods are challenged.