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Dissolved air flotation reduces suspended solids in biofloc for shrimp farming

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By Milthon Lujan

Graphical representation of the equipment used in bench-scale tests to remove total suspended solids using the dissolved air flotation (DAF) method in Penaeus vannamei culture under biofloc conditions. Source: Galasso et al., (2024); Aquacultural Engineering.
Graphical representation of the equipment used in bench-scale tests to remove total suspended solids using the dissolved air flotation (DAF) method in Penaeus vannamei culture under biofloc conditions. Source: Galasso et al., (2024); Aquacultural Engineering.

Imagine raising thousands of shrimp in a tank with minimal water changes. Sounds risky, right? But biofloc technology is based on this very principle, creating a self-sustaining ecosystem where beneficial microbes manage waste. However, excess suspended solids can still cloud the water, affecting shrimp health and growth.

For shrimp producers seeking super-intensive production with minimal environmental impact, maintaining optimal water quality is key. The accumulation of suspended solids in biofloc systems, while beneficial in some aspects, can pose challenges.

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This research reveals a promising solution: dissolved air flotation (DAF) technology. Scientists from the Federal University of Santa Catarina investigated the effectiveness of DAF in removing total suspended solids from super-intensive white shrimp (Penaeus vannamei) culture under BFT conditions.

They evaluated various parameters such as saturation pressure, time, recirculation rate, air-to-solids ratio, and flotation velocity to optimize water quality maintenance.

The challenge of suspended solids

Biofloc systems, popular for their efficient waste management, may experience increasing levels of suspended solids, affecting oxygen levels and potentially harming shrimp. Traditional removal methods are often impractical or limited.

Settling tanks (sedimentation) remove some solids but struggle with lighter particles. Water renewal is effective but wastes water and resources. Other options, such as centrifugation and membrane filtration, are efficient but energy-intensive.

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The answer: Dissolved air flotation (DAF)

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This research presents a promising solution: dissolved air flotation (DAF). By injecting small bubbles into the water, DAF gently lifts and removes unwanted particles, leaving water in improved quality conditions.

This promising technology attaches air bubbles to suspended solids, causing them to float for easier removal. Unlike sedimentation, DAF effectively handles lighter particles.

Potential benefits of DAF:

  • Improved removal: Studies show that DAF can remove 95% of turbidity, 30% of total organic carbon, 94% of bacteria, and 97% of algae, outperforming sedimentation by 5% to 40%.
  • Nutrient recycling: Removed solids (sludge) contain valuable nutrients, potentially reducing waste disposal costs.
  • Sustainability: Compared to water renewal, DAF conserves water and resources.
  • Faster startup: DAF units can start operating quickly, minimizing downtime.
  • Smaller footprint: DAF requires less space than traditional settling tanks.
  • Oxygenation: The process can add oxygen to the water, benefiting shrimp health.

DAF is widely used in water treatment but remains underexplored in aquaculture, particularly for solids removal. The study tested a DAF model. By adjusting air pressure and recirculation rate, researchers achieved up to 60% removal of total suspended solids, significantly improving water quality.

Benefits for shrimp farming

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But the advantages go beyond solids removal:

  • DAF achieved impressive removal rates of up to 60% of total suspended solids, significantly improving water clarity.
  • It also demonstrated significant potential for removing other harmful substances, including:
  • Turbidity: Average removal of 80%
  • Biochemical oxygen demand (BOD): Average removal of 50%

It is important to note that DAF maintained crucial water quality parameters such as alkalinity, pH, temperature, and salinity within ideal ranges for shrimp health.

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Performance optimization

The study identified optimal configurations for DAF in biofloc systems:

  • Saturation pressure: Above 4.5 bar
  • Recirculation rate: Over 15%
  • Flotation velocity and air-to-solids ratio varied depending on the setup, indicating potential for further optimization.

Conclusion

DAF has the potential to revolutionize sustainable biofloc shrimp farming by offering efficient and environmentally friendly solids removal. The research aims to contribute to its broader adoption and optimization in the aquaculture industry.

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This research demonstrates the immense potential of DAF for shrimp aquaculture. With further development and optimization, DAF could become a game-changer, enabling sustainable and productive super-intensive shrimp farming while safeguarding the environment.

The study was funded by the Federal University of Santa Catarina and the Coordination for the Improvement of Higher Education Personnel (CAPES).

Contact
Marco Shizuo Owatari
Aquatic Organisms Health Laboratory – AQUOS, Aquaculture Department, Federal University of Santa Catarina (CCA/UFSC), Rodovia Admar Gonzaga 1346, CEP 88040-900 Florianópolis, SC, Brazil
Email: owatarimarco@hotmail.com

Reference (open access)
Galasso, H. L., Owatari, M. S., Arana, L. A. V., & Lapa, K. R. (2024). Effects of scaled-down dissolved air flotation system on suspended solids removal from Penaeus vannamei culture under biofloc conditions. Aquacultural Engineering, 102396.