70%–80% of the nutrients (N, P, and C) used to feed fish and aquatic animals are released into the water as dissolved and solid excretions resulting in environmental pollution. As an al ternative to the conventional nitrification followed by water exchange or denitrification, assimilation -based biofloc technology (BFT) is used to in-situ convert aquaculture excretions ( with an additional external carbon source) into protein-rich microbial biofloc. BFT is primarily used in shrimp and tilapia pond culture, and was shown to enhance feed conversion efficiency, biosecurity, and wastewater recycling.
We suggested employing BFT within a side assimilation reactor to integrate the idea of ammonia assimilation into microbial biomass within intensive recirculating aquaculture systems (RAS). This reactor relies on activated sludge under microaerophilic conditions, with the fish-rearing water and solid excretion continuously circulating through it. To address the challenge of high outflowing turbidity, we introduced a submerged ultrafiltration membrane bioreactor (MBR), which led to an average turbidity in the fish of less than 25 NTU. The system offers numerous advantages over conventional RAS and traditional BFT methods. These include exceptional water reuse rates, energy conservation, and minimal waste generation. Notably, the biofloc boasts a protein content of approximately 40%, a substantial increase compared to aerobically based BFT systems which typically contain around 20% protein. Additionally, the system’s low oxygen requirements have led to a remarkable reduction in daily energy demand, potentially by as much as 75%. Furthermore, comprehensive assessments have been conducted to evaluate its environmental impact and economic viability.
Dry microbial biofloc was utilized as a component in fish feed, replacing 15%, 20%, and 25% of the original feed, to examine its impact on fish growth, survival, and disease resistance. Across all groups, fish survival reached 100%. While the control group exhibited slightly higher weight gain (~15%) compared to the biofloc-fed group, the latter demonstrated significantly superior survival rates post-bacterial challenge (89% survival), contrasting with the control (58% survival, p = 0.01). Variations in immunity were also observed based on the origin of the external carbon source, with semolina proving more efficacious than sugar (Fig. 1). Furthermore, an economic analysis underscored the potential advantages of implementing biofloc commercially.