Membrane Fouling Characteristics In Integrated Aerobic Granular Sludge And UF/NF Process

The aerobic granular sludge has the advantages of small equipment area,good effluent quality and stable operation.In this study,AGS was integrated with UF/NF process to treat the simulated domestic wastewater and produce reuse water.Scanning electron microscopy(SEM),Fourier Transform Infrared Spectroscopy(ATR-FTIR),Atomic Force Microscopy(AFM)and Contact Angle Test Methods were used to analyze membrane fouling.AGS reactor,UF and NF exhibited high removal efficiency for COD(51.33%,90.48% and 99.26%)and nutrients(53.63 %,94.84% and 98.06% total nitrogen,and 49.8%,97.07% and 98.73% phosphorus),indicating that the integrated aerobic granular sludge and UF/NF process could provide high pollution removal and quality reuse water.As for filtration behavior of UF and NF,shear stress produced by agitation speed could significantly improve flux,due to the dispersion of pollutants.Besides,for AGS,improved simultaneous nitrification and denitrification by the internal anaerobic,anoxic,and aerobic structure and the richer biological community increased foulant removal,while the larger pore size and mature structure also reduced foulant deposition.Moreover,shear stress also diminished the total fouling resistance,reversible fouling and irreversible fouling,as well membrane cleaning efficiency was promoted,by controlling AGS deposition on membrane.Overall,the results demonstrated an alternative option for water treatment and reuse water production in an integrated AGS and membrane process.Increasing the stirring speed improved the thickness of the hydraulic boundary layer and the average shear rate of the membrane surface.TMP enhanced membrane filtration resistance.wet-sieve analysis was adopted to screen AGSs with various sizes.The 35-mesh particlehad lowest flux and greatest filtration resistance,while it was the main foulants.In addition,the results of SEM,ATR-FTIR,AFM and contact angle tests showed that large AGS and mature structure were beneficial to reduce UF membrane fouling.Small size organic components in UF permeate,including polysaccharides,proteins,humic acid and fulvic acid were the main NF foulants.The total amount of fouling layer on the membrane surface reduced after chemical cleaning.The surface hydrophilicity was not the main factors affecting membrane fouling.The results showed that the main membrane fouling mechanisms for AGS-UF/NF integrating process were membrane pore blocking and cake formation.