**1. Introduction**

Oxygen transfer in water is a key component in environmental technologies, for example, in wastewater treatment, by virtue of the efficiency of the transfer of oxygen and the total costs of the air injection process, and water treatment itself is common in many industrial applications, for example, in the chemical, hydraulic, and nuclear industries, for which biphasic air-water flow characterization is required for each particular case. For example, for water treatment, energy consumption is the highest for aeration processes, as compressed air is an expensive working medium. The same behavior occurs in aeration for biological purposes, for example in fish farming, or in water aeration downstream of

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

hydraulic turbines, in which the design of the aeration systems (orifice diameter, configuration, operating conditions, and location) may significantly improve the quality of turbine aeration [1, 2]. The aerator design parameters are used to determine the best balance between oxygen transfer (volume of air injected and size and shape of generated bubbles) and energy consumption.

Aerators (spargers) can be made from porous ceramic or metallic materials, fritted (sintered) glass, or plastic, each having specific features in emitting bubbles to increase the contact surface between the gas and the liquid.

In literature, the volumetric mass transfer coefficient Kla was also obtained in situ, [3–6], for different configurations. As the configuration and operating conditions are far from this experiment, a direct comparison cannot be performed.

The main objective of this study is to optimize an aeration device, that is, to achieve the best dissolved oxygen (DO) transfer versus minimized energy consumption for injection. The classical experiment of an ascending bubble column was used to compare many injection devices. The aeration devices are mainly perforated metallic plates (MPs). Two parameters are studied: orifice size and arrangement. As a control, the active admission area is kept constant for all configurations. The injection air flow rate is controlled and the main aeration parameters (Kla and standard oxygen transfer rates [SOTR]) measured. Comparison of standard aeration efficiency (SAE) is also recorded. The efficiency results are compared with two other aerators, that is, a ceramic plate (CP) and a glass plate (GP). Finally, the optimized configuration in terms of SAE (best compromise between dissolved oxygen transfer and energy consumption for the air injection) is chosen.
