Physical Mechanism Of Membrane Fouling Based On Mixed Liquid Rheology

Membrane fouling was well understanded in chemical mechanism and microbial also,while comparable limited understanded in physical mechanism.Mixed liquid in anaerobic membrane bioreactor treating high strength organic wastewater demonstrated significant non-Newton flow behavior,where physical mechanism contributed outstandingly to the membrane fouling.Therefore,the work start from foulant motion to understand which flow characteristics impacted the motion from mainstream,wall flow to cake layer and gel layer and its impacting factors.The work characterized the rheology characteristics and factor of anaerobic mixed liquids,cake layer and gel layer,developed augmentation strategy of mixed liquid rheology based on particle sized distribution.The rheology based fouling mitigation strategy was also develop per the physical mechanism and the mechanism was validated in real project by historical data.,to promote the understanding of physical mechanism of membrane fouling and support the fouling mitigation.The foulant motion starting from detached out of mainstream of mixed liquid to cake layer and gel layer through wall flow,and ultimately went into and blocked the membrane pore was systematically reviewed with a physical perspective.The wall flow function and related stress on foulant was theoretically analyzed,which revealed the limitations of the wall function when applied in the non-Newton fluid conditions in anaerobic digestion.The work also combed characteristics and factors of anaerobic mixed liquid,and proposed the research implications,content and technical roadmap.To characteristics rheology of anaerobic mixed liquid,the work investigated the mixed liquid rheology of digested food waste,and developed manipulation strategy of the anaerobic mixed liquid.Results indicated that the rheology was significantly impacted by dissolved organic matter(TS≤2%)and particles(TS≥4%).Increased temperature decoupled the particles to small organics,which enhanced he rheology.Augmentation with larger particles improved flowability,while small particles forms loosely fractions with lower fractal dimension.The proposed augmentation strategy improved flowability as well as methane yield of the anaerobic digestion.To promote the understanding of physical mechanism of membrane fouling,the rheology of foulant was sophisticatedly analyzed in an anaerobic membrane bioreactor treating leachate of food waste.An fouling mitigation strategy was therefore proposed and theoretically validated based on the existed data series in an full-scale membrane bioreactor treating domestic wastewater.Results highlighted the importance of mixed liquid rheology in fouling.The rheology of mixed liquid and cake layer was similar in shear thinning while differences remains in a significantly gradient from mixed liquid to cake layer and gel layer.The shear thinning suggested that higher shear rate could improve flow conditions and mass transfer in the wall flow,and therefore promising in mitigating fouling.A numerical model was developed for hollow fiber membrane using computational fluid dynamic software to investigate the impaction of mixed liquid rheology on vortex-induced vibration in staggered layout of membrane units.Results demonstrated that Strouhal number and the vibration frequency achieved the optimized valued at MLSS 15000 mg/L.The optimized mixed liquid suspended solid was consisted with the experimental optimized mixed liquid suspended solid,which provided novel physical mechanism and insight for fouling mitigation.The proposed fouling mitigation strategy was mechanically validated in the 150000 m~3/day membrane bioreactor treating municipal wastewater,which deepen the physical understanding of membrane fouling,supported the fouling mitigation by novel technology and validated mechanism.