Promoting circular economy: Comparison of novel coupled aquaponics with anaerobic digestion and conventional aquaponic systems on nutrient dynamics and sustainability

Aquaponics presents promising green technology for food security and climate change. This study investigated the performance and nutrient dynamics in a novel aquaponics with onsite anaerobic treatment compared with conventional decoupled and coupled aquaponics. All systems demonstrated good performance with fish survival rates of >97 %, feed conversion ratios of 1.3, and high lettuce production of 6.9–11.8 kg/kg-feed. The recovery of N and P (from their concentrations in the feed) was 21 % and 16 % respectively in the decoupled aquaponics, and 24 % and 18 % in the coupled aquaponics. Recovery of N and P in the novel aquaponics was 41 % and 36 %, respectively, which led to enhanced total nutrient utilization efficiency of 76 % N and 80 % P. The latter was due to the high recovery of N and P from the fish sludge. 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 other tested (conventional) systems. It was postulated that coupled aquaponics with anaerobic digestion is a sustainable solution that may promote a circular economy, especially in arid zones with high radiation and temperature.