Enhancement On Water Treatment Efficiency And Mechanism By Micro-nano Bubbles During Ultrafiltration Process

Water pollution poses a great threat to human life.Ultrafiltration（UF）membrane separation has been widely applied to water treatment given its high efficiency,safety and small footprint.However,natural organic matter such as humic acid（HA）,bovine serum albumin（BSA）and alginate（SA）will aggravate membrane fouling and decline the efficiency of water treatment during UF,which has become the main obstacle to its wide application.In recent years,micro-nano bubbles（MNBs）are widely used in membrane separation because of their unique properties.It is of great significance to study the effect of MNBs on the efficiency of UF separation.Firstly,the effects of air flow rate,feed rate and solution p H value on the enhanced UF membrane process by MNBs were studied.When the air flow rates are 0-160 m L min^-1 and the feed rates are 15-45 m L min^-1,the normalized flux is enhanced to 1.17-1.40 and the rejection coefficient is enhanced by 8%-17%;When p H value is 6.0,the normalized flux and rejection coefficient are the most significantly enhanced.Secondly,the properties of MNBs were characterized by dynamic light scattering（DLS）,laser scanning confocal microscope（LSCM）,turbidity test and zeta potential.DLS results showed that the size distribution of MNBs produced by MNB-generator is21.04-955.4 nm and MNBs would coalesce and collapse with time;LSCM results showed that the filtrate contained MNBs（50 nm）with an average diameter less than the pore size of UF membrane（10-90 nm）;The turbidity increased rapidly by 1.1-1.7NTU with MNBs input and decreased to be consistent with that of pure water（0.9 NTU）with the attenuation of MNBs;The zeta potential of MNBs in water is-2.74-2.21 m V.Finally,the mechanism of the enhances UF membrane process was studied by SEM,FTIR,CFD simulation and apparent viscosity test.The results showed that MNBs did not change the surface properties of UF membrane and the chemical properties of pollutants;The viscosity test results showed that the apparent viscosity of gas-liquid mixture decreased with MNBs input,which enhanced the normalized flux.This study provides new insights into the importance of MNBs in membrane separation and broadens the research vision of other chemical processes.