曝气池清水曝气气泡云团形态特征

Based on the investigation of the operation conditions for different wastewater treatment plants around the world,it is found that the distribution of the air bubbles in the aeration tank is not uniform in temporal and spatial scale,which in turn results in the difference of oxygen transfer.The effluent quality and the operation cost would be affected accordingly.The experiments were conducted in a plug-flow aeration tank model in which the oxygen transfer in clean water was measured.The high speed camera and digital image processing technique was employed to investigate the shape and variation characteristics of air bubble cloud.The air flow ratios of a single diffuser disc are 0.25 m³/h,0.5 m³/h,1.0 m³/h and 2.0 m³/h,respectively.The results showed that the ratio of axis length to water depth is around 1.03 to 1.30,with the identical shape of flow velocity distribution.The cloud axis length and bubble residence time increased first and then decreased as the air flow rate increased.The air bubble cloud shape became irregular and the shape variation frequency was high as the increasing of air flow ratios.For multiple aeration disc design,the bubble plume upstream had an effect on the shape of bubble plume downstream,and the width of bubble plume was almost the same in both air flow direction and lateral direction.The average width of bubble plume was greater at the position of 0.8h₀and 0.5h₀than that at 0.2h₀.The width of bubble plume at different water depths varied with time,and the trend was more significant at 0.8h₀.For air discharge rate 0.25 m³/h,1.0 m³/h and 2.0 m³/h,the average width of bubble plume was 1.0~1.5,1.6~2.5 and 1.75~3.5 times of the diameter of the aeration disc,respectively.There are mainly three regions of bubble plume in plug-flow aeration tank,namely,the adjustment region at the bottom area,the free surface region and the turbulent diffusion region at the middle,with different bubble mechanics and kinematics characteristics.With the increase of air flow discharge,the residence time of air bubble increased and then decreased with the diffusion width.These characteristics of bubble plume may provide theoretical support on the numerical simulation of bubble mechanics and kinematics in plug-flow aeration tank.