Study On Mass Transfer Characteristics And Optimization Of Bubble Plumes In Micro-aeration Oxidation Ditch Under Complex Flow Conditions

The micro-aeration oxidation ditch technology utilizes microporous aerators and submerged push-flow equipment to operate in tandem to achieve aerated oxygenation and mixed circulation motion.The wastewater treatment efficiency and effluent water quality are closely related to the process of aeration and oxygenation.At the same time,the aeration system is also the most energy-consuming part of the entire process.Therefore,it is necessary to study the hydrodynamics and characteristics of mass transfer of the bubble plume in the process of micropore aeration system.So far,the research of hydrodynamic behavior and oxygen mass transfer mechanism of the bubble plume with complex fluid environment in the micro-aeration oxidation ditch are still not deep enough.In view of the above-mentioned facts,water and carboxymethyl cellulose sodium?CMC?solution was used as liquid phase to conduct experimental study,the aeration and oxygenation performance of Newtonian and non-Newtonian fluids under micro-aeration oxidation ditch with complex flow conditions was investigated.Based on the theory model of oxygen mass transfer,the flow characteristics and oxygen mass transfer mechanism of bubble plume in the transver velocity condition was studied.The oxygen volume transfer coefficientK _La₂₀,oxygenation capacity SOTR,oxygen utilization factor SOTE,and power efficiency SAE were used as quantization parameters for the best operating conditions of the system.The main research work and results are as follows:?1?Experiments were conducted in pilot test to explore the effects of aeration volume,horizontal flow intensity and aerator arrangement on aeration and oxygenation performance of the system.The study shows that the oxygen mass transfer coefficient increased when there exists horizontal flow of the ditch,but the system power efficiency is not absolutely positively related to this;the uniform layout of the microporous aerator can increase the oxygenation capacity by 35%,which is beneficial to the oxygen transport process;The increase of aeration can increase the effect of oxygen transfer,but the change of oxygen utilization is contrary to this.The flow velocity of the mixed liquid in the channel change with the increase of the horizontal flow intensity;at the same horizontal flow intensity,the velocity of the liquid near the baffle is the largest,and the flow velocity at the position of the outer wall of the channel is the smallest;The flow velocity in the middle of the oxidation ditch is greater than that at the bottom,and the velocity at the top is the lowest at the same cross section.Evenly deploying two small power impellers can achieve a better flow effect than a single high power,with greater horizontal flow velocity and the spatial distribution is more uniform.The study on the factors influencing the oxygen transport performance of the microporous aerator can provide a theoretical basis for the realization of energy saving and optimization of operating parameters in the micro-aeration oxidation ditch wastewater treatment system.?2?Based on the flow characteristics and mass transfer mechanism of bubble plumes in Newtonian fluids,the CMC solution with different mass fractions was used to simulate the non-Newtonian liquid-phase environment of wastewater,combined with transverse flow effect,the change rule of bubble plume movement and oxygen transfer in power-law fluid was investigated.After comprehensive comparison,it is found that the rheological properties of the liquid phase has a great influence on the spatial distribution of oxygen flow and oxygen transport in the micro-aeration oxidation ditch.The higher the concentration of CMC in the solution,the more significant the obstruction of the oxygen transfer process.?3?The bubble size in the process of aeration and oxygenation was analyzed,and deeply understand the regularity of the Sauter mean diameter of the bubble during mass transfer,and establish physical equations between bubble,dimensionless parameters such as Re,We,and Fr in different liquid-phase environments to quantify the effect of various operating factors.At the same time,according to the transverse flow conditions in the annular channel,the mass transfer method was theoretically calculated by the dimension analysis method,and the oxygen volume transfer coefficient prediction model was proposed,and the correlation coefficient between experiment and theory above 0.98.The high degree of coincidence calculation can better predict the effects of oxygen transfer in Newtonian and non-Newtonian fluids.