| Activated sludge process is a mature leading process in wastewater biological treatment,and many new wastewater treatment processes have been evolved in the process of development,which has become the main treatment method of wastewater biological treatment.The biomass of biofilm method is 5-20 times that of activated sludge.Times.Aerobic granular sludge has the advantages of the above two technologies in the treatment of aerobic organisms at the same time.Moreover,the device can also play a good role in the treatment of some anaerobic organisms.Therefore,the research on the rapid formation of aerobic granular sludge has great research value.Flexible mesh can provide a good carrier for the growth of biofilm in the reactor.When the growth of biofilm on the mesh is mature,with the increase of hydraulic shear force on the water-crossing section,the mesh will flutter,and some biofilm will fall off,so as to increase the value of activated sludge in the system and create for the formation of granular sludge.(2)According to the principle of karman vortex street and the network flow,the reaction pool water cross section is set on a string of flexible screen,control screen aperture and the scale of the network at the same time,make a sheet of vortex and the floc size in the same order of magnitude,or a similar order of magnitude In this case,the vortex motion will be able to control of reaction pool,we also may according to the biological floc law of flocculant and grew up in the reaction pool to biological flocculation pool design,improve the efficiency of biological reaction pool,promote the formation of granular sludge's condition.At the same time,the mesh plate optimizes the flow field,creates a hydrodynamic environment,forms Karman Vortex Street after the mesh,creates a good hydraulic condition for biofloc coagulation,and screens the initial particles by oscillation to accelerate the formation of granular sludge.The main research content of this paper is to simulate the flow field in the reactor,and verify it with PIV technology to find out the most suitable factors affecting the rapid formation of granular sludge in the reactor.(1)The mechanism of granular sludge formation showed that the flow of mixed liquid in the bioreactor was in turbulent state,and turbulent motion could promote the mixing of substances and increase the diffusion rate.When a mesh plate is set on the cross section,the flow field behind the mesh will appear approximately isotropic turbulence.The structure and energy distribution pattern of the turbulence will be changed by the setting of the mesh plate,and the mass transfer process of the turbulence will be adjusted and optimized with the setting of the mesh plate.Therefore,different grids can be set in the appropriate position of the reactor to adjust and optimize the turbulent flow field,improve the reactor efficiency,and then accelerate the process of activated sludge granulation.(2)According to the principle of Karman vortex street and water flow through the network,the parameters of the grid forming stable Karman vortex street are simulated,the aperture and the size of the mesh are controlled,so that the size of the vortex and the floc is in the same order of magnitude,or the order of magnitude is similar,and the reaction cell with the material of machine glass is designed.The parameters of the reaction pool are as follows:the cross-section area is connected in series along the direction of water flow,300 cm ~2,200cm~2,375 cm~2in turn,and the net plate is placed in the vertical direction in the formation area of the condensation center.There are six layers of net plate,the space between the net plate is250 mm to 330 mm,the diameter of the net rope is 2 mm to 4 mm.The designed inflow of the simulation experiment device is 50 L/h to 150 L/h.The reflux ratio is 50%to 150%.(3)Through the steady-state simulation of single-phase flow field and gas-liquid two-phase flow field by Fluent software,the optimum hydraulic parameters are determined according to the relatively stable generation of Karman Vortex Street,i.e.the diameter of mesh rope is 4mm,the size of mesh hole is 1.0cm2,the spacing of mesh plate is 290mm,and the air-water ratio is 8:1.(4)Through PIV experiments of water single-phase and gas-liquid two-phase,it can be seen that the experimental parameters are:diameter of mesh rope 4mm,spacing of mesh plate290mm,inlet flow 80L/h,air-water ratio 8:1,mesh hole size 1.0cm~2.The stable state of Karman vortex street and flow field is successfully acquired,and the formation speed of vortex is under the action of micro-bubbles.It has been improved.It is consistent with the best hydraulic control condition of hydraulic simulation. |
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