Understanding Aeration for Marine Livewells & Baitwells Pt.2

Surprising Findings in Waste-Water Treatment Research

Recent waste-water treatment research has revealed air flow limits and aerator depth design for maximized oxygen transfer efficiency.

Important conclusion reached via this research: Fine bubble diffusers along with fine bubble jet
aerators both offer the highest oxygen transfer efficiency. Fine bubble Jet aeration provides a 25% Oxygen Transfer Efficiency!

OTR – Oxygen Transfer Rate:

We find this research in ‘Analysis of oxygen requirements and transfer efficiency in a wastewater treatment plant, by Marius-Daniel Roman and Mircea-Vlad Mure’an; Technical University of Cluj-Napoca, Romania International Journal of Latest Research in Science and Technology; ISSN (Online):2278-5299 Volume 3, Issue 2: Page No. 30-33 , March-April, 2014 https://www.mnkpublication.com/journal/ijlrst/index.php

Three important conclusions were reached via this research:

1. For good system performance the rate of supplied dissolved oxygen should
equal the rate of oxygen consumption.
2. Fine bubble diffusers have the highest oxygen transfer rate per unit energy.
3. Oxygen transfer rate takes place from the rising bubbles as produced by the
fine bubble diffuser.

Conclusion of Research Paper 1: This paper validates the Power-Jet’s use of fine bubble diffuser design!

OTR – Oxygen Transfer Rate, Continued Pt.2:

Proceedings, Workshop Toward an Oxygen Transfer-Standard by Marius-Daniel Roman and Mircea-Vlad Mure’an; Technical University of Cluj-Napoca, Romania; International Journal of Latest Research in Science and Technology;
ISSN (Online):2278-5299 Volume 3, Issue 2: Page No. 30-33 ,March-April, 2014 https://www.mnkpublication.com/journal/ijlrst/index.php

Conclusion of Research Paper 2: This paper validates the Power-Jet’s use of a (fine bubble) Jet aerator design!

OTR – Oxygen Transfer Rate, Continued Pt.3:

Improvement of oxygen transfer efficiency in the activated sludge process; 2nd International Conference on Civil & Environmental Engineering IOP Conf. Series: Earth and Environmental Science 476 (2020) 012098;
Kan et.al School of Environmental Engineering, University Malaysia Perlis, (UniMAP)

Two important conclusions reached:

1. The deeper the air diffuser submerged into the tank, the longer the bubble pathway to travel up to surface leading to fine bubble diameter extending its surface contact area between bubble and the water; thus creating a higher aeration coefficient value.
2. Researchers have shown that the deeper (from 1.5 m to 2.0 m) the aeration diffuser, the higher oxygenation efficiency (from 20% to 50%). The authors here show that a 150 mm depth diffuser depth has good agreement although the diffuser depth was way deeper
than reported by other researchers.

These findings begin to touch on minimum diffuser depth to achieve sufficient bubble pathway travel. Because passively aspirated aerators are sensitive to differential pressure of the air feed line to the immersed depth of the venturi tube, there are limits to the depth of installation. Campau touches upon this: “. . . Aspiration vacuum must be sufficient to overcome the water pressure created by the depth at which aerator is situated.”

150 mm depth (6 inch) Minimum Aerator Installation Depth

Three additional important conclusions reached:

3. The experiment found that the airflow rate range between 5L/min to 7 L/min provided the best Oxygenation Efficiency as shown in Figure 2 but further experimentation needs to be conducted.
4. The air flow regime also depends upon the rate of the air flow from the diffuser . . . with a probability to create heterogeneous regime bubble formation (bubbles reform to larger bubbles by coalescence) which leads to less oxygenation efficiency.

5. Some research has shown there is a strong correlation between Oxygenation Efficiency and bubble hydrodynamics. Therefore, in this experiment, the improvement of oxygen transfer with respect to Oxygenation Efficiency can be shown that the air flow rate can be adjusted to the optimum range of 5L/min to 7L/min.

oxygen-transfer-coefficient-vs-air-flow-rate

Conclusion of Research Paper 3: This paper validates 5-7 liters per minute aspiration air flow = best "efficiency"!

OTR – Oxygen Transfer Rate, Continued Pt.4: Putting the Chemistry, Biology, & Research all together

Summary Constraints & Requirements:

5 - 7 liters per minute air flow for max jet aerator efficiency
150 mm (6 inch) minimum aerator depth
Air = ~20% Oxygen
500 mg O2/kg fish per hour @ 20C (Boyd)
1000 mg O2/kg fish per hour @ 30C (Schramm & Heidinger)
25% Oxygen Transfer Efficiency

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