**5. Conclusions**

This chapter presents an experimental study for the global optimization of aeration in the industrial configuration. For optimization two main parameters were considered: aeration performance (dissolved oxygen transfer) and energy consumption for the air injection.

*ai* [mm<sup>2</sup>

*C*0

*Cs*

*g* [m/s<sup>2</sup>

*Q* [m3

*Qs* [m3

*Pb*

*R*0

*r*0

] interfacial area of the all bubbles in the system *C* [mg/l] concentration of dissolved oxygen at the moment *t*

[mg/l] concentration of dissolved oxygen at the moment *t* = 0

regression) at working temperatures

CP ceramic plate with volume porosity in the range 45–50%

tions of 100%

100% (*C*<sup>20</sup> = 8.62 mg/l)

*D* [mm] diameter of the plate MP (*D* = 44.8 mm)

*d* [mm] diameter of a hole in the plate MP

0.25–0.315 μm

Kla20 [1/min] Kla, corrected at temperature 20°C

*N* number of holes on an MP

/s] air flow rate injected through the MP

*nb* number of bubbles in the system *nb* <sup>=</sup> *<sup>V</sup>*

*Ps* [Pa] standard atmospheric pressure (1 atm)

[m] the initial air bubble radius

[m] radius of the hole

[Pa] atmospheric pressure at the time of testing

*H* [m] hydrostatic head on aerator (*H* = 0.8 m)

*dp* [mwc] pressure drop on the aerator

DO dissolved oxygen

] gravity

*Cst* [mg/l] concentration of dissolved oxygen at saturation, at the surface, at working

[mg/l] concentration of dissolved oxygen at saturation (estimated by non-linear

*Cs*20 [mg/l] concentration of dissolved oxygen at saturation, corrected at temperature

GP fritted (sintered) glass plate with porosity controlled in the range

MP 0.1–2.4 interchangeable perforated metallic plates with circular holes of 0.1–2.4 mm

Kla [1/min] volumetric mass transfer coefficient (estimated by regression)

Klat [1/min] Kla, volumetric mass transfer coefficient at the moment *t*

/s] air flow rate at standard conditions: *Qs* <sup>=</sup> *<sup>Q</sup>* <sup>⋅</sup> 273.15 \_\_\_\_\_\_\_\_\_

*P* [W] the power consumed for the injection of air through the aerator

temperature, at standard pressure of 1 atm, and relative humidity condi-

Experimental Study of Standard Aeration Efficiency in a Bubble Column

http://dx.doi.org/10.5772/intechopen.76696

365

20°C, at standard pressure of 1 atm, and relative humidity conditions of

(273.15 + *t* 0)

\_\_\_\_ *voit Vb*

Was considered many injection devices: two series of metallic plates with different designs (the arrangement of aeration holes, hole shapes, and diameter) and hole diameters between 0.2 and 2.4 mm, ceramic plates, and glass plates in an air bubble column in water. The investigations where performed for the following air flow rates: *Q* = 180, 360, 480, 600, 720, 960, 1140 l/h. The aeration performances were obtained, using the procedure of the standard procedure ASCE 2-91/1993 (Kla and SOTR), and compared with other literature results. The results are coherent for the tendencies and the differences were explained.

Based on these results and injection loss measurements, the SAE—standard aeration efficiency—was calculated for all plates and global efficiency curves were plotted.

Taking into account these parameters in an aerator design, and optimizing the total efficiency, allows for an efficient deployment of aeration devices in industrial systems. As variations in efficiencies for dissolved oxygen transfer, or losses, in different aeration devices can be greater than a factor of 10, the findings of this optimization study are significant for achieving the best design of aeration systems for hydraulic turbines and in water treatment and so on in regulation to the specific needs and capacity of each application (available air flow rate, pressure of injection, aeration need, etc.).

This study shows the importance of the optimization of the aerator device in terms of materials, aperture arrangement, aperture shape, aperture dimension for the specific conditions of each application (air flow rate, pressure gradient, emplacement of the aeration device), and for the best global efficiency—best compromise between the energy needed for the injection of the air and the quantity of dissolved oxygen obtained by the aeration process.

In the next step, these results and the detailed bubble flow morphology [12] will be used to validate numerical simulations for dissolved air transfer, to realize the sparger optimization by numerical calculations.
