Aquaponics (integration of aquaculture and hydroponics) is gaining renewed interest in enhancing food security (FAO, 2022), with decoupled (DAP) and coupled (CAP) systems as their common types (Baganz et al., 2021). However, several limitations, including resource and energy demand, nutrient imbalances, and waste management, have limited their widespread application (Palm et al., 2023). Efficient onsite treatment of fish sludge and plant wastes as renewable resources to reuse nutrients (e.g., N and P), recover energy and recycle water is a promising solution (Zhu et al., 2023, 2022). Zhu et al. (2021) demonstrated that aquaponics wastes could be efficiently treated using anaerobic digestion (AD). We investigated the nutrient, water and energy balances in DAP, CAP, and a novel zero-discharge off-grid aquaponics system with UASB (CAP-AD). We also evaluated the efficacy of nutrient recovery from the UASB in improving crop yields and resource use efficiency. The experiments were conducted in a desert aquaponics facility in a greenhouse with RAS and an adjacent net-house containing deep water culture hydroponics at Ben-Gurion University of Negev, Israel. Catfish (Clarias gariepinus) were stocked density of ~50 kg/m3 with daily feeding of 2% of the total stocking biomass. Lettuce seedlings (Lactuca sativa cv. Noga) were introduced on floating rafts of the hydroponics. Following a stabilization stage, the system was closely monitored for four months. An input-output model was developed to support balances for the three aquaponics (Zhu, 2023).
All systems demonstrated good performance in producing fish and vegetable products. Typical fish performance was observed with survival rates >97% and feed conversion ratios from 1.21 to 1.33. In addition, 33% of the total input N and 37% of the P were recovered from fish sludge via AD, yielding a high total nutrient utilization efficiency of 76% N and 80% P. The novel system also demonstrated 1.6´ higher plant areal productivity, 2.1´ lower water usage, and 16% less energy consumption per kg of feed relative to the (traditional) DAP and CAP systems. Biogas production was 0.84 m3/kg for fish sludge and 0.67 m3/kg for dry plant material, which supported about 84% of the energy demand for its operation. CO2 sequestration was 1.4 higher than the feed carbon, which reduced the system’s carbon footprint by 64%. Coupling anaerobic digestion with aquaponics has significant potential utility for increasing system efficiency and promoting the circular economy by treating and reusing waste streams, especially in arid zones.