Development Of A New Aerator And Its Application

Aeration plays an important role in wastewater biological treatment, and it is also a major way to purify polluted river. The aerator is the core of dissolved oxygen aeration process, it has a direct impact on the effect of wastewater biological treatment and energy consumption. Forcing on the need of aerator effect in water treatment, an aerator with new structure was developed in this study. The gas-liquid two-phase flow was analyzed by Computational Fluid Dynamics（CFD） simulation, the aeration characteristics were investigated by oxygenated clean water test. At last, the role of aerator in purification of polluted river was explored.This paper introduced a new aerator, variable pitch helical blade assembly in the inner of it was the key. The gas-liquid mixture forms a complex swirling gas-liquid two-phase flow under the action of variable pitch helical balde assembly, radial pressure gradient and axial pressure gradient were generated internally, mass transfer interface got expanded and secondary flow appears in the new aerator, which improved the oxygen transfer efficiency effectively. At the same time, the gas, water molecules, a variety of suspended soids and macromolecular organic group flowing through the aerator got cutted and refined, greatly increasing the mass transfer between the substance and improving the removal of contaminants. The new aerator owned the features of simple constructure、small size、no-blocking and easy maintenance.Computational Fluid Dynamics（CFD） simulation method basing on mixure model and Realizable k-s turbulence model was used to conduct steady analysis of the gas-liquid two-phase flow. The results showed that radial pressure gradient and axial pressure gradient were generated in the inner of the new aerator. Secondary flow was produced in radial plane, with the superposition of secondary flow and mainstream, the turbulence intensity of gas-liquid two-phase flow got strengthened, which reduced the thickness of gas film and liquid film on the sides of gas-liquid contact interface and improved the mass transfer of gas and liquid.The aeration characteristics of the aerator were studied by oxygenated clean water test, and the results showed that the new aerator had good aeration properties. When the liquid flow rate was 12m3/h and the gas flow rate was 400L/h, the mass transfer coefficient of oxygen KLas was 0.39 min^-1, the oxygenation capacity q_c was 0.0429 kg/h, the oxygen utilization efficiency ε was 32.49%. With the increase of gas flow rate, mass transfer coefficient of oxygen and oxygenation capacity increased gradually, however, the oxygen utilization efficiency decreased. Increasing the liquid flow rate, mass transfer coefficient of oxygen, oxygenation capacity and oxygen utilization efficiency were increased. But the variation law of the aerator’s oxygenation performance with gas and liquid flow rate did not meet linear relationship. With the same gas flow rate, the new aerator had higher oxygen saturation and less time reaching the saturation, its mass transfer coefficient of oxygen KLaS, oxygenation capacity q_c and oxygen utilization efficiency ε were approximately four times as large compared to the microporous aerator.The new aerator was used to improve the water quality of polluted river. The results showed that the new aerator could increase the dissolved oxygen quickly, eliminate the peculiar smell of river water and achive the purification of water quality. Compared with the microporous aerator, the removal rate of COD_Mn, NH₃-N, TN and TP were enhanced 13%,78.1%,3% and 3.5% respectively.