Combination of Surface and Diffused Aerators in Term of Oxygen Transfer Efficiency and Energy Performance

Abstract

Paddle wheels are widely used in aquaculture pond in Thailand due to convenient installation and operation, with an ability to supply oxygen together with making water circulation as their advantage. But the low oxygen transfer efficiency (OTE) and energy performance (Aeration efficiency, AE) should be considered as the main drawback of this aerator type, because they can make a contacting area between air (oxygen) and water at the water surface only. While diffused aerators present a high OTE and AE. However, their mixing performance in the vertical direction is not enough for a large aquaculture pond. Then it is necessary to apply another equipment to perform water flow or horizontal water circulation, such as axial propellers, water pump, or paddle wheels. To fulfill this gap, a combination aeration system was setup by combining the diffused aerators and water pumps: diffused aerators play the role for an oxygen transfer mechanism, while water pumps creating a horizontal circulation for the oxygen distribution. It was found that the highest AE (0.47 kg-O2/kW-hr) was obtained when applying 57 mm/s of the horizontal water velocity during the aeration by 2 sets of the flexible rubber tube diffuser. This AE value was closed to 0.51 kg-O2/kW-hr of 3 sets of diffusers, and higher than a system contained by 2 units of 60W water pumps, (which represented as a paddle wheels system) up to 47 times. The uniform DO distribution was obtained by 57 mm/s of the horizontal water velocity, and the improvement of oxygen transfer was obtained by reducing of bubble size (dB) and their rising velocity (UB) which can produce more interfacial area (a-area) up to 278%. Moreover, both of oxygen transfer parameters and bubble hydrodynamic parameters can be predicted accurately by the theoretical prediction models with an error lower than 10% for the combination aeration system that can be used as a criterion for the aeration system design.