| Micro-bubbles can increase the oxygen content in water,enhance the activity of aerobic microorganisms,improve the ability of organic degradation,and have been widely used in water pollution control.Among them,the micro-bubble aeration technology as a new aeration technology,compared with the traditional bubble and small bubble aeration technology,it has many advantages,such as long residence time in water,high oxygen mass transfer efficiency,high adsorption efficiency and generation of strong oxidation free radicals,has the potential to mitigate Bioaerosol generation and dispersal.However,the characteristics of dissolved oxygen and the rules of Bioaerosol formation and dispersion are not clear.In this paper,the behavior of micro-bubbles in pure water and sewage under turbulent flow is studied,the influence of different factors on the dissolved oxygen mass transfer in micro-bubbles was simulated and the mathematical regression equation was established.Andersen sampling-microbial culture method was used to analyze the variation of Bioaerosol concentration and particle size,the exposure risk of Bioaerosol produced by aeration of micro-and nano-bubbles was discussed.The main conclusions reached are as follows:（1）The physical properties of micro-bubbles are stable,and the aeration time does not affect the number and size of micro-bubbles.The operating parameters of micro-bubble generator affect the size and concentration of micro-bubble,and indirectly affect the dissolved oxygen characteristics of micro-bubble aeration.Therefore,the operation parameters of micro-bubbles were optimized,and the results showed that,under the inlet pressure of 0.3 Mpa and the inlet flow rate of 60±10 ml/min,the air flow rate of micro-bubbles was increased,the micro-bubble aeration can produce bubbles with an average concentration of 2.9×107P/ml and an average particle size of 221.5 nm.The mass transfer coefficient of dissolved oxygen in micro-bubble aeration is KLA=1.96 min-1,SOTR and SOTE are 9.32 and 6742 times of the traditional aeration,2.88 and 1558 times of the small bubble aeration,respectively,have a better ability to oxygenate.（2）The turbulence degree in the flow field has a great influence on the dissolved oxygen in the micro-bubbles.When the turbulence dissipation rateεis 6.987,7.766,8.133 and9.574,the KLa is-0.0195,-0.0306,-0.0407 and-0.0469,respectively,the results show that the dissolved oxygen rate of the micro-bubbles increases and the time of the bubbles in the water decreases with the increase of the turbulence degree.The effect of temperature and partial pressure of oxygen on dissolved oxygen mass transfer in micro-bubbles is more significant than that of turbulence,the regression equations of dissolved oxygen mass transfer with temperature,partial pressure of oxygen and turbulence are as follows:KLa=0.023+5.91×10-4A+5.76×10-4B-2.08×10-4C-1.46×10-5AB+5.13×10-6BC-3.99×10-7AC-5.67×10-6A2-7.33×10-5B2-1.19×10-7C2。（3）Micro bubble aeration can effectively reduce the production and fugitive amount of microbial aerosols,and compared with the traditional medium bubble and small bubble aeration methods,the concentration of microbial aerosols produced is reduced by 38.53%and 37.68%,respectively.The concentration distribution of microbial aerosols produced by the fine bubble aeration process decreased significantly with the increase of horizontal distance,while the distribution was relatively balanced at different heights at the same horizontal distance,and the microbial aerosols were mainly distributed above the aeration liquid surface.The particle size of microbial aerosols was mainly distributed between 1.1～4.7μm,and the non-carcinogenic risk index HI<1,the non-carcinogenic risk caused by the fine bubble aeration process was low,and the biodiversity of the treated water body was changed,pathogenic bacteria such as Acinetobacter still existed,and the risk of pathogenic bacteria transmission caused by microbial aerosol exposure still needs to be considered. |
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