Rapid Start-up Technology Of Aerobic Granular Sludge-Simulation And Application Of Gas-liquid Two-phase Flow In A Wire Rope Reactor

Aerobic granular sludge is a new biological treatment technology for sewage and wastewater,which has broad development prospects domestically and abroad.A large number of studies show that aerobic granular sludge has the dual advantages of activated sludge process and biofilm process.At the same time it also enjoy the function of partial anoxic and anaerobic biological treatment,showing unique advantages in biomass,oxygen utilization rate,treatment effect etc.However,the domestic researches show that aerobic granular sludge biological treatment technology also has serious technical,economic and managing problems.The above problems make the aerobic granular sludge not effectively realizing its engineering application.The problems are mainly manifested in the difficultyof aerobic granular sludge formation,long time of start-up cycle,needing high shear force and high gas-water ratio,making the processing kinetic energy increasingly,economic performance poorly and other problems.In view of the above reasons,an experimental model of aerobic granular sludge with continuous flow combined rectangular structure was designed and the size of the model was l×b×h=2000 mm×1000 mm×250 mm.The experimental model consisted of two parts:aerobic granular sludge coagulation center formation area and aerobic granular sludge formation and treatment area.A net rope reactor is additionally arranged in the coagulation center forming area of the model to serve as an aerobic granular sludge quick start promoter.In the study,The effects of different hydraulic control parameters on the rapid start-up of aerobic granular sludge were studied.Firstly,the gambit software was used to draw the actual model mesh,then,the RNG k-?model and the gas-liquid two-phase flow two-fluid model was used to simulate the water single-phase and gas-liquid two-phase flow respectively by fluent software.Thus the changes of different geometric parameters and hydraulic parameters were studied,and the optimal hydraulic control conditions for aerobic granular sludge rapid start-up were obtained by analyzing the dat.Then,the particle velocity field instrument?PIV?tracer technique was used to compare and analyze the numerical simulation results of the optimal hydraulic control conditions with the PIV measured results,so as to confirm the accuracy of the numerical calculation.Finally,the optimal hydraulic control conditions were applied to the actual model of microbial experiments,respectively in four different materials?nylon,nylon 6,PE,nylon 66?under the net rope aerobic granular sludge fast start-up experiment,from the sludge formation time,sludge stability,sludge formation process to select the most appropriate net rope material.The removal rates of COD_cr,BOD,SS,TN,TP,ammonia nitrogen and chroma were detected when the microbial model was running stably,and checked whether the model met the first-class B standard of pollutant emission standard of urban sewage treatment plant.In order to achieve the purpose of aerobic granular sludge fast start,and provide data basis and theoretical basis for its practical engineering application and reasonable design.The main conclusions are summarized as follows:?1?Numerical simulation and PIV verification?1?When the geometric parameters are as follow:mesh size is 1.0 cm²,mesh diameter is4 mm,mesh spacing is 290 mm,the Karman vortex street is formed in the area of the back end of the mesh when the water flows around the mesh.Vortex generation and shedding can occur after water flows through each screen plate.Resulting in an increase in hydraulic shear force,which contributes to the attachment of flocculent sludge;And the free flocculent biomembrane can collide with each other to form primary granular sludge;And is favorable for that primary granular sludge to smoothly reach the granular sludge for area by utilizing continuous high hydraulic shear force.?2?When the hydraulic parameters are 80L/h and 8:1,vortex street not only increases the collision probability of flocculent sludge under the action of micro bubbles,but also provides the required high hydraulic shear force for shaping granular sludge,thus further effectively promoting the rapid start-up of aerobic granular sludge.?3?By comparing the simulation and PIV vortex results under the same flow rate,the same mesh size,the same mesh diameter,the same mesh spacing,and the same gas-water ratio,the agreement between the two images and velocity vector values is as high as 95%,which fully verifies that the optimal hydraulic control conditions obtained by computer simulation are accurate and feasible.?2?Microbial experiment in a net rope reactor?1?The particle size distribution of four kinds of net ropes made of cotton fiber,PE,nylon66 and nylon 6 were compared and the results show thatthe particle size distribution of aerobic granular sludge in nylon 6 was in accordance with the normal distribution rule,which indicated that the aerobic granular sludge system in nylon 6 rope reactor could run stably.?2?Quality index of effluent after aerobic granular sludge stabilization,namely COD_cr,BOD,SS,TN,TP,ammonia nitrogen and chroma,all meet the first-level b standard of the pollutant discharge standard of urban sewage treatment plant,and completely achieve the purpose of rapid start-up of aerobic granular sludge.