Simulation Study Of The Performance Of Aerobic Granular Sludge Under Gradient Feed And The Flow Regime In The Reactor

In Xinjiang,tomato paste processing produces a large amount of highly concentrated wastewater.Wastewater has seasonal characteristics,short cycle and large discharge,which easily causes pollution to surface water.As the emerging wastewater treatment technology in recent years,Aerobic Granular Sludge（AGS）has the advantages of good settling performance,high biological phase,high toxicity resistance,strong shock load resistance,multiple biological efficacy,etc.,which most ordinary activated sludge can hardly match.Consequently,the use of AGS to treat tomato paste processing wastewater has some practical value.In this paper,the flocculant sludge was inoculated in intermittent SBR reactors R1 and R2 at room temperature,and artificially prepared tomato paste wastewater was used as the influent matrix,and the step influent COD concentration was used to cultivate AGS,so as to explore the influence of gradient influent change on the morphology of AGS,physicochemical characteristics of sludge,sewage removal efficiency and microbial community structure.Fluid dynamics model was established to simulate the change of apparent gas velocity and influent COD concentration on the flow state in the reactor,and to analyze the influence mechanism of the two factors on sludge granulation.（1）After both treatments R1 and R2 were stable,it took 15 d and 30 d for the initial formation of granular sludge.At 70 d,the particle size was 780μm and 1060μm,respectively,and the internal skeleton was composed of massive aggregates and filamentous bacteria;R1 and the SVI₃₀ of R2 is reduced to about18 m L/g and 32 m L/g,respectively,and the maximum MLVSS is 7900 mg/L and 7031 mg/L,respectively;protein andα-polysaccharide mainly constitute the skeleton of AGS,andβ-polysaccharide is distributed on the surface of particles,the total cells accumulated at the outer edge of the particles;the average removal rates of COD,NH₃-N,PO₄^3--P in wastewater reached 95.2%,96.03%,92.07%and 93%,89.54%,89%,respectively.（2）At the phylum level,Proteobacteria and Bacteroidetes are the dominant phyla;At the class level,Betaproteobacteria,Alphaproteobacteria,and Bacterodia are the dominant bacterial classes;at the genus level,Zoogloea and Flavobacterium is the dominant genus.Sphingobacteriia,Negativicutes,Flavobacteria were significantly negatively correlated with COD,NH₃-N and PO₄^3--P;Gammaproteobacteria and Clostridia were significantly positively correlated with COD and NH₃-N;Betaproteobacteria was significantly positively correlated with PO₄^3--P.Proteobacteria has denitrification effect;Bacteroidetes is related to EPS degradation;Acidobacteria has a positive effect on the initial coagulation of flocculent sludge.A large number of AOB,NOB,PAOs and GAOs are present in mature AGS.The abundance of Delta-9 desaturase and Transport system permease protein is higher;Lactocepin,Linoleoyl-Co A desaturase and Ribosomal protein S6 modification protein changed most significantly,but the microbial enzymes in the whole system maintained similar functions.（3）It is found that the granular sludge is susceptible to the influence of apparent gas velocity and inlet gas flow rate through numerical simulation of the flow pattern in the reactor,and the annular flow formed by the inlet gas flow will change to vortex flow as the apparent gas velocity and particle size increase.The larger the particle size,the greater the relative velocity at the same apparent air velocity,and the magnitude of the relative velocity is related to the compressive force on the particle surface.The larger the relative velocity between the liquid phase and the granular sludge at different apparent gas velocities,the greater the shearing effect on the particle surface and the increasing frequency of friction between the sludge and the water flow,which is conducive to the formation of spherical structures of the particles.In the water intake with different gradients,the flow phenomena in the reactor are dominated by annular and vortex flow,and the flow distribution is responsible for the irregularity of the particle morphology.