Formation Of Aerobic Granular Sludge And Membrane Fouling Analysis In An Enhanced Membrane Bioreactor

Our previous studies succeeded in cultivating aerobic granular sludge?AGS?directly in an internal-circulation membrane bioreactor?IC-MBR?operating with continuous flow.This work made some improvements of IC-MBR to get an enhanced-internal-circulation MBR?EIC-MBR?.The purpose of this work was to explore the formation mechanism of GS and the characteristics and variation of membrane fouling.The EIC-MBR was fed with synthetic wastewater,which had a COD:N:P ratio to be100:5:1.The influent concentration increased gradually.The inoculated sludge was collected from the secondary sedimentation tank of a wastewater treatment plant and its initial concentration was 1800 mg/L MLSS.The inoculated sludge was acclimated with high concentration synthetic wastewater to allow the filamentous bacteria to grow up before the EIC-MBR was inoculated.Then the EIC-MBR was operated for 113 days without discharging any sludge except small amount for sampling.The concentration of COD_cr and inorganic nitrogen in effluent and MLSS,MLVSS,SV of sludge were analyzed with standard methods.Hot extraction method,Lowry method and anthrone-sulfuric method was applied to analyze the EPS of sludge.The granule size and it distribution of sludge was analyzed by a laser particle size analyzer.Wet density analysis,SEM observation,enzymatic hydrolysis,staining and HTS analysis were also accepted to characterize the formed AGS in the EIC-MBR.Quantitative analysis was also applied to analyzed membrane fouling.Sludge on the membrane module was analyzed by granule size,EPS and HTS analyses.The membrane module itself was observed under SEM and FM.Anaerobic-anoxic-oxic condition was found in the EIC-MBR and the removal rate average COD_crr of was 91.60%,while the removal rate of TN fluctuated.MLSS was on the rise and the maximum could reach 12000 mg/L.A significant linear positive correlation was found between MLSS and sludge apparent viscosity.Brown naked-eyes-observable AGS was found day 36,while black and yellow color AGS with many filamentous bacteria stretching around and without filamentous bacteria was found on day 75.Diverse AGS with at least four types of color were observed on day113,including black AGS,yellow AGS,black-margin and yellow-middle AGS and white-margin and black-middle AGS.The results of wet density,SEM observation,staining and HTS verified that these AGS with different colors were different kinds of AGS indeed and also heterogeneity existed in every single kind of AGS.Filamentous bacteria were demonstrated to play an important part in EPS fixation.This work verified that diverse AGS could be formed with same carbon source in a single reactor,whose main reasons were diverse micro-habitat caused by different DO distribution and the complex internal circulation in the EIC-MBR.MLSS and sludge apparent viscosity did more in TMP increase than granule size,but granule with smaller size was easier to be accumulated on the membrane module.SMP was the major reason of membrane fouling and the influence of PS on membrane fouling was larger than PN.The HTS results verified that flocculent sludge was easier to be accumulated on the membrane module.And it could be concluded that EPS could be washed by physical and chemical cleaning.Overall,this work verified that diverse AGS could be formed with same carbon source in a single reactor and thus provided research directions for mechanism research and practical application of AGS.