Study On The Influence Of Hydraulic Conditions In Bioreactor Based On Bubble Behavior Analysis

With the improvement of wastewater discharge standards,biofilm and aerobic granular sludge have attracted widespread attention due to their dense physical structure,high concentration of biomass,no need for sludge return equipment,and strong organic load carrying capacity.The hydraulic conditions is great significance to the efficiency of wastewater treatment.Aeration can provide dissolved oxygen,generate hydraulic shear stress and change the characteristics of the flow field,which is the key in the whole treatment process.However,the current research on aeration is mainly focused on dissolved oxygen diffusion and mass transfer,related research from the perspective of fluid mechanics is very limited.There is insufficient research on the hydrodynamic characteristics of aeration and the influence mechanism of control parameters,which limits its application in practical industry.Aiming at the above problems,the paper establishes the relationship between bubble characteristics and hydraulic.By improving the aeration parameters and optimizing the hydraulic conditions of the reactor,it provides technical support for the energy conservation and consumption reduction of the wastewater treatment process.The effect of bubble behavior on the hydraulic disturbance in the reactor was simulated of gas-liquid two phase flow.The simulations obtained the distribution of bubble velocity and turbulent dissipation power under different height-to-diameter ratio(H/D),aeration intensity and bubble diameter.The results showed that when theheight-to-diameter ratio was 7,the average turbulent dissipation power reached the maximum and the hydraulic disturbance became weak due to the bubble velocity decrease.With the aeration intensity increasing,the influence range of turbulent dissipation did not change significantly,but the turbulence intensity increased significantly.However,due to the fluid resistance,increasing the aeration intensity had limited effect on the gas-liquid two phase velocity gradient.As the bubble diameter decreased,the amplitude of the sloshing of the air column increased,the influence range of turbulent dissipation became larger,and the hydraulic disturbance increased.Based on the bubble behavior,the effected of aeration intensity and bubble diameter on the hydraulic shear stress in FBBR were studied.The results showed that the hydraulic shear stress produced by aeration was more uniform and effective,and was not affected by the reactor depth.Increasing aeration intensity can improve the hydraulic shear stress,but affected by fluid resistance it will cause energy waste.As the bubble diameter decreased,the amplitude of the sloshing of the air column and the turbulent dissipation influence range increased.This strengthened hydraulic shear stress.The hydraulic conditions of complex gas-liquid-solid three phase were simulated in the sequencing batch reactor(SBR).Analyzed the hydraulic shear stress and solid holdup distribution combined with image scanner.The results showed that increasing the height-to-diameter ratio reduced the accumulation of particles at the bottom and strengthen the hydraulic shear stress.Because of liquid resistance,the effected of aeration intensity on the hydraulic shear stress was limited.Reducing the bubble diameter helped the partical accumulation.And the influence range of turbulence increased,which resulted in stronger hydraulic shear stress.When circular aeration was used,the particle distribution was more uniform,and the hydraulic shear stress was increased by 1.18 times.At last,put a scheme of inserting baffles and changed single point aeration into two point aeration.which can increase hydraulic shear stress without increasing the energy consumption and changing the aspect ratio.It provided a reference for the practical application of the granular sludge reactor.