| Wastewater treatment is an important part of water resources protection project,which is highly regarded by people.Traditional wastewater treatment technology can utilize activated sludge to remove pollutants from water.But there are problems such as slow separation of mud from water and low efficiency of wastewater treatment.Aerobic granular sludge technology is a new type of biological wastewater treatment technology,which can greatly improve the mud separation rate and wastewater treatment efficiency by granulating the flocculent activated sludge.However,aerobic granular sludge technology is still in the experimental model stage,mainly because there is no suitable aerobic granular sludge reactor for industrial applications.In order to design a new aerobic granular sludge reactor,it is necessary to know the flow field environment of granular sludge formation.Thus it is very important to study the state of gas-liquid two-phase flow in aerobic granular sludge reactor.In this paper,firstly we used the flow field visualization technique to observe the bubble motion state in the cylindrical aerobic granular sludge reactor.And the local liquid flow field in the reactor was measured by PIV test technique.It is found that the bubble flow moved in a spiral swing way.And the faster the gas velocity,the greater the amplitude of the bubble flow swing.Affected by the bubble movement,the liquid flow in a circulation way of the center up and around down.When the ventilation rate is increased to 4 cm/s,the maximum axial liquid velocity increases to 19.6 cm/s.Due to the swing movement and wall,a lot of large-scale vortex is distributed in the liquid flow field,and the size and position of the vortex are changing with time.CFD technology was used to study the effects of gas velocity,liquid level and reactor diameter on the gas-liquid two-phase flow field in aerobic granular sludge reactor.were discussed.The results show that the gas velocity and the reactor diameter are the main parameters that affect the state of the gas-liquid two-phase flow field.Changing the gas velocity and the reactor diameter will significantly change the flow field characteristics such as gas-liquid two-phase flow morphology,axial liquid velocity and liquid turbulent kinetic energy.But in the HID ratio of 6 to 10,the liquid level has little effect on the gas-liquid two-phase flow field characteristics.Two prismatic aerobic granular sludge reactors with polygonal cross-section shape were proposed.The structure of polygonal prism reactor was designed by using the principle of hydraulic radius equality.It is found that the gas-liquid two-phase flow field in the polygonal prism reactors and cylindrical reactor is similar through compared the flow field characteristics such as gas-liquid flow morphology,axial liquid velocity and liquid turbulent kinetic energy of three reactors by numerical simulation.Finally,aerobic granular sludge with the largest particle size of 3.5mm is successfully cultivated in the polygonal prism aerobic granular sludge reactor through the experiment of aerobic granular sludge culture.It is proved that the polygonal prism aerobic granular sludge reactor can be used for the culture of aerobic granular sludge. |
PDF Full Text Request