The Distribution Of Microbubbles And Their Interaction With Flocs In The Treatment Of Emulsified Oil Based On Air Flotation

Air flotation is a clean and efficient technology to remove pollutants in water,which is widely used in the treatment of oily wastewater and other related fields.This study focuses on the multiphase flow pump air flotation process,studies the characteristics of micro-bubble in the air flotation tank and the relationship between micro-bubble and oil droplets and flocs,and explores the influence of various factors on the oil removal efficiency in the treatment of emulsified oil wastewater by multiphase flow pump air flotation process,which enriches the understanding of multiphase flow pump air flotation process and provides a basis for the popularization of this technology.Based on the Multiphase pump air flotation process,this experiment has carried out the micro and macro experimental research on the process.In the microscopic aspect,firstly"static adhesion microscopic observation method"is used to calculate and observe the particle size distribution of micro-bubble in the air floating tank under different operating conditions.Secondly,the self-made micro-bubble volume concentration measuring device was used to measure the micro-bubble volume concentration distribution in the air floating pool.Finally,the"dynamic microscopic observation system"was used to observe and analyze the interaction among micro-bubble,oil droplet particles and flocs,and the two-dimensional fractal dimension of different flocs was counted.The relationship between the two-dimensional fractal dimension of flocs and its treatment effect on wastewater containing emulsified oil was investigated.Macroscopically,this study focused on pilot air flotation tank,explored the promotion effect of foaming agent on the treatment of oily wastewater by multi-phase flow pump air flotation process,and focused on the influence of various factors on the oil removal performance of the treatment of emulsified oil-containing wastewater by multi-phase flow pump air flotation process.The results show that,the particle sizes of micro-bubble in the contact zone and laminar flow zone of the air floating pool conform to the normal distribution of positive skewness.After the micro-bubble escape from the dissolved air release head,with the delay of sampling location,the micro-bubble constantly collide and coalesse,and the particle size of micro-bubble becomes larger and larger,and the distribution of micro-bubble becomes more and more uneven.The particle sizes of the micro-bubble in the contact zone are in the range of 50-100μm,and those in the laminar flow zone are in the range of 70-150μm.The volume concentration of micro-bubble in the air flotation tank basically varies from 1.0m L/L to 5.0m L/L.In the absence of flocs,the effect of micro-bubbles on oil droplets is mainly"contactless flotation",and only a small number of micro-bubbles will adhere to oil droplets.In the process of air flotation,air flotation flocs are different from precipitated flocs,while air flotation flocs need loose structure and large voids,which is beneficial to combine with air flotation micro-bubble,obtain greater flotation performance and come into contact with more oil droplets.The flocs generated by the flocculant selected in the process of air flotation should have smaller two-dimensional fractal dimension.Through the pilot test,it is concluded that the most reasonable operation parameters of Multiphase pump dissolved air floatation process are as follows:dissolved air pressure 0.32 MPa,air-water ratio 6%,reflux ratio 50%,surface load 5.33(m~3/m~2·h).Under these operating conditions,the removal rate of emulsified oil wastewater is 85.94%,and the effluent turbidity can reach 5.92NTU.The addition of reasonable foaming agent can obviously improve the removal performance of emulsified oil by Multiphase pump air flotation process.