| In the context of the scarcity of available water resources in China,the scarcity of water resources per capita,the increasing annual discharge of wastewater and the relative backwardness of wastewater treatment facilities,it has become necessary to protect the water resources environment and to conduct research on the optimization of wastewater treatment systems.Aeration tank is an important reaction vessel for wastewater purification by activated sludge method in wastewater treatment plants,and it is of practical significance to study the structural optimization of aeration tank.In this paper,CFD computational fluid dynamics method is used to numerically simulate the aeration process in the tower type aeration tank and the circulating mixed type aeration tank,to change the aeration hole arrangement of the two types of aeration tanks,to compare and analyze the simulation results to study the effect on the internal hydraulic characteristics of the aeration tank,find the best arrangement and complete the study on the optimization of the aeration tank equipment structure,so as to provide reference for the optimization of the aeration tank in the actual engineering wastewater treatment system.The main contents include:(1)Experimental data were referenced to model the aeration tank experimental setup and perform numerical simulation calculations,the VOF multiphase flow model and the RNG k-εturbulent flow model are used and the boundary conditions of the model are set.The numerical simulation results are compared with the experimental reference results and the analysis shows that the numerical simulation is effective and the various hydraulic characteristics and phenomena inside the simulated model are consistent with the characteristics of the gas-liquid two-phase flow in the actual aeration basin and the numerical analysis results of the model are basically consistent with the experimental results in all aspects,which proves that the selected mathematical model can be applied to the numerical simulation study of the aeration process in the aeration tank.(2)Three sets of working conditions were set up to ensure the same size,number and inlet velocity of the aeration holes,and the sparseness of the bottom aeration hole arrangement was changed to study the numerical simulation of the tower type aeration tank model.The simulation results of different conditions were compared and analyzed in terms of flow field structure,flow velocity distribution,and gas content rate size.The results show that when the spacing of aeration holes at the bottom is 22 mm,i.e.,the aeration holes are evenly arranged,the distribution of flow lines in the tower aeration tank is more dense and smooth,and the flow velocity is more evenly distributed,which means that the mixture flows better and the gas-liquid mixing is even and sufficient.The model contains the largest gas rate,and the dissolved oxygen content in the pool is sufficient,so the effluent treatment effect is more ideal and more efficient.(3)The model of circulating mixed aeration tank was established,three sets of working conditions were set up to ensure the same aeration volume,the arrangement of aeration holes at the bottom of the model was changed,and the influence of the arrangement of aeration holes on the internal hydraulic characteristics of the circulating mixed aeration tank was studied by numerical simulation.The results show that when the aeration holes are arranged in three uniform rows,the flow lines in the straight channel section of the aeration zone of the circulating mixed aeration tank model are more dense and smooth,and the flow is good;the aeration hole arrangement has no significant effect on the average flow velocity in the horizontal section,but when the aeration holes are evenly arranged,the aeration area has a greater proportion of high flow velocity,the most uniform flow velocity distribution,stable flow field,good mixing effect of gas-liquid two-phase,and high efficiency of oxygen transfer to the non-aeration area;when the aeration hole arrangement of working condition three is adopted,the model has the largest overall air content inside,which is conducive to the efficient operation of the whole wastewater treatment system. |
