I+R+D

Improve RAS oxygen levels with low-cost pipe diffusion aeration (PDA)

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By Milthon Lujan

RAS. Source: Nofima
RAS. Source: Nofima

Maintaining optimal oxygen levels is crucial for a healthy and productive recirculating aquaculture system (RAS). Traditionally, diffuse aeration with blowers and diffuser stones has been the preferred method, but it can be complex and costly.

Research conducted by scientists from Huzhou University (China) and Zhejiang University investigates the effects of oxygen flow rate (OFR) or inlet dissolved oxygen (IDO) combined with pipe length (PL) on the performance of pipe diffusion aeration (PDA). They constructed a referable mathematical model of outlet dissolved oxygen (ODO) using IDO and gas-liquid contact time (CT) for real recirculating aquaculture water.

Limitations of traditional aeration systems

The limitations of traditional aeration systems include:

  • Short bubble contact time: Bubbles rise quickly in shallow tanks, limiting oxygen transfer to the water.
  • Interrupted waste collection: Air bubbles can disrupt water flow, making it difficult to remove solid waste.
  • Inefficient for biofilm reactors: While aeration is used for biofilm contact, it has minimal impact on increasing dissolved oxygen.
  • High energy consumption: Blowers used in diffuse aeration can consume a lot of energy, increasing operating costs.

What is PDA?

PDA is a simple, low-cost, and easy-to-maintain system for increasing dissolved oxygen levels in RAS using pure oxygen. It uses readily available components such as a diffuse aeration stone, a T-joint, and an inner plug connector.

The science behind PDA

This study investigated the impact of various factors on PDA performance. The researchers examined how oxygen flow rate (OFR), inlet dissolved oxygen (IDO), and pipe length (PL) influence the system’s effectiveness in increasing outlet dissolved oxygen (ODO).

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Key findings

The researchers reported the following results:

  • Pipe length matters: For tap water, increasing pipe length (PL) led to higher oxygen increase rates and oxygen utilization rates.
  • RAS water is different: In real recirculating aquaculture water, lower IDO resulted in a higher oxygen increase rate.
  • Ideal for long pipes: PDA is particularly suitable for RAS with long pipes, as pipe length significantly influences performance.
  • Predictable DO levels: The study developed a mathematical model to predict outlet DO based on factors such as IDO and gas-liquid contact time. This allows precise control over DO levels in aquaculture tanks.

Promising results for RAS

Under specific test conditions, PDA achieved a significant oxygen increase rate (149.02%) and a good oxygen utilization rate (11.60%). This demonstrates the potential of PDA as a reliable and cost-effective solution for oxygenating recirculating aquaculture systems.

Why choose PDA for your RAS?

PDA offers a promising solution for maintaining optimal DO levels in RAS. Its simplicity, affordability, and effectiveness make it a valuable tool for aquaculture operators seeking to:

  • Improve fish health and growth.
  • Reduce operating costs.
  • Increase energy efficiency.
  • Simplify maintenance routines.

Benefits of PDA for RAS operators

  • Cost-effective: The simple design and readily available components make PDA an economical solution.
  • Low maintenance: The system requires minimal maintenance, reducing operating costs.
  • Effective for long pipes: Ideal for RAS with extensive pipe networks.
  • Predictable DO levels: The mathematical model allows precise control over dissolved oxygen in culture tanks.

Conclusion

The research team plans to explore the integration of PDA with liquid oxygen supply systems, aiming further to enhance its applicability and efficiency in RAS operations.

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PDA offers a promising alternative for maintaining optimal DO levels in RAS. Its simplicity, affordability, and effectiveness make it an attractive option for aquaculture producers. As research continues, PDA has the potential to become a game-changer for sustainable and efficient RAS management.

The results of this research add to other developments such as the “perforated pooled circular stepped cascade aerator (PPCSC),” nanobubble technologies, and the use of artificial intelligence to improve the management of RAS.

The study was funded by the Rural Revitalization Project of Huzhou and the Open Subject of Key Laboratory of Equipment and Informatization in Environment Controlled Agriculture (Ministry of Agriculture and Rural Affairs).

Contact
Haijun Li
College of Biosystems Engineering and Food Science, Zhejiang University
Hangzhou 310058, China.
Email: lhjahau@zju.edu.cn

Reference
Ji, M., Ye, Z., & Li, H. (2024). Performance evaluation and mathematical model of pipeline diffused aeration for recirculating aquaculture system. Aquacultural Engineering, 105, 102410. https://doi.org/10.1016/j.aquaeng.2024.102410