Enhancement of nitrogen transformation in media-based aquaponics systems using biochar and zerovalent iron.

Aquaponics combines aquaculture and hydroponics, offering methods to produce fish and plants. However, optimization of its nitrogen transformation processes, which would lead to higher nitrogen utilization efficiency (NUE) and lower nitrous oxide (NO) emission, is still a daunting challenge. This study investigated these issues by using biochar and zerovalent iron (ZVI) with low (LD) and high (HD) doses. Results showed that LD improved NUE by 15%, reaching 57%, along with a significant 36% reduction in NO emissions. Conversely, denitrifying bacteria were disturbed in HD due to incomplete denitrification, resulting in higher NO emissions. Microbial analysis showed that the abundance of denitrifying bacteria increased from 12% to 24% in LD, compared with the control, leading to lower NO emissions and optimized nitrogen cycling. These findings suggested that using the appropriate proportion of biochar and ZVI would be a promising approach to enhance the sustainability and productivity of aquaponics systems.