Effect Of Hydraulic Shear Conditions Based On Hydrocyclone Separation On Formation Of Aerobic Granular Sludge

Because aerobic granular sludge（AGS）has the characteristics of high nutrient removal efficiency,small floor area and fast sedimentation rate,AGS shows great potential in wastewater treatment.However,the process also has the disadvantages of long start-up time and low system stability.In this study,the cultivation of AGS was strengthened by hydrocyclone separator,flocculant and electrocoagulation,and computational fluid dynamics（CFD）.Firstly,the granulation process of AGS in SBR with cyclone separator（SBR-HS）and conventional SBR culture process is compared,and then the conditions to enhance the formation of AGS are studied by adding flocculant and electrocoagulation.Finally,CFD simulation is used to predict the effects of different hydraulic conditions and carrier particles added into hydrocyclone separator on flow field and AGS separation effect.The main research results of this paper are as follows:The experimental results of hydrocyclone coupled SBR show that the introduction of hydrocyclone has no obvious effect on granulation.Although SVI is greatly reduced,MLSS is also reduced.In the small-scale experiment,SVI decreased from 71.2 m L/g to 22.1 m L/g,and MLSS decreased from 3.2 g/L to 1.8 g/L.In the pilot experiment,the values of MLSS and SVI in SBR were maintained at 4.4±1.9 g/L and 100.9±18.7 m L/g respectively,and the values of MLSS and SVI in SBR-HS were maintained at 4.2±3.2 g/L and 46.0±9.3m L/g respectively.This is because the hydrocyclone provides strong shear force and centrifugal force.The removal rates of NH₄⁺-N and TIN by SBR-HS were 28.3 mg/（L·h）and8.2 mg/（L·h）,which were significantly higher than those by SBR.The hydrocyclone separation experiment shows that short-time hydrocyclone is conducive to improve the settleability.The average particle size changes from 390μm down to 82μm when the swirl time was 5 min/h.But the average particle size decreased to 66μm when the swirl time was20 min/h,showing that long-time swirl was not conducive to the formation of AGS.Although the introduction of hydrocyclone improves the denitrification efficiency and EPS content,there are no obvious large particles in the system.Therefore,the coagulation process is considered to strengthen the granulation of suspended sludge.The response surface method shows that the dosage of flocculant is an important factor affecting the coagulation effect,and the particle size of flocculant and the dosage of PAM have little effect on the coagulation effect.With the increase of flocculant dosage,the proportion of particle size greater than 0.25 mm increased to 27%by adding 6 g/L new volcanic rock flocculant.In the process of electrocoagulation,the metal is anodized and dissolved into metal cationic flocculant through the action of applied voltage,so as to shorten the granulation time.Through the analysis of response surface analysis,it is concluded that the best electrocoagulation conditions were electrode plate spacing of 3.5 cm,voltage of 20 V and time of 12.5 min.After electro flocculation,the particle size of 0.2-2.0 mm accounted for61.11%,and the average particle size is 410μm.The computational fluid dynamics simulation details the granulation and particle separation efficiency of the hydrocyclone.The results show that the separation efficiency of400μm particle size reached 97%at the flow rate of 0.3 m/s.The particle separation effect reached the best.In the traditional SBR,although the addition of carrier particles could strengthen the granulation process in a short time,the separation performance of different carrier particles was very different.The carrier with larger particle size and density had shorter residence time in hydrocyclone separator and was easy to be separated.The separation efficiency of biochar was 70%,GO-NPs was 34%,GAC,ceramsite and limestone was 98%.According to the separation efficiency,large particle size carriers such as activated carbon and ceramsite are recommended.In summary,through the research on the experiment and simulation of hydrocyclone separation coupled SBR,it is clear that the hydraulic hydrocyclone conditions provided by hydrocyclone separator improve the AGS sedimentation,but also slow down the growth of particle size.The particle size of AGS can be improved by adding flocculants and electrocoagulation.The best hydraulic conditions and carrier ions are predicted by CFD simulation,which provides a theoretical basis for AGS process innovation and reactor design.