Research On The Characteristics Of Ultrafiltration Membrane Filtration Interface Potential And The Formation Process Of Pollution Layer

How to understand the membrane fouling process more deeply is the core issue of effective control of membrane fouling,and is also the key to guide the optimization and efficient and stable operation of membrane modules.In this paper,the membrane fouling behavior and characteristics of typical organic foulants were studied by Zeta potential monitoring and ultrasonic time domain reflection(UTDR)combined with synchronous on-line monitoring,in order to establish a scientific method for analyzing and evaluating membrane fouling.Firstly,the membrane fouling process was monitored synchronously in situ with Zeta potential,and the changes of interface potential during membrane fouling were characterized in real time.It was found that the change trend of Zeta potential was different in different stages of membrane fouling.Zeta potential decreased rapidly during the blocking stage.When Zeta potential declines slowly,it was the formation stage of cake layer.Zeta potential tends to be stable when it transferred from the cake layer to the compaction stage.Because the membrane surface has been covered by foulants in the experimental membrane,the membrane surface potential completes the transition from the membrane intrinsic potential to the foulants intrinsic potential,and the potential value after stabilization hardly changes.On the basis of this study,the membrane fouling process was studied by using the method of"accumulation of membrane fouling in different time intervals"and the characteristic parameter of membrane potential ?Zetaft2t1 was introduced as the evaluation index,and Pearson correlation coefficient was analyzed with the irreversible fouling resistance of membrane.It was found that the irreversible fouling degree of membrane in different time intervals was negatively correlated with the change of Zeta potential on the surface at the initial stage of membrane filtration.The experimental results show that the most violent change of Zeta potential is the main accumulation stage of irreversible membrane fouling in the filtration process,and the accumulation of irreversible membrane fouling will accelerate the membrane filtration to a stable stage.Under the same conditions,the cumulative amount of irreversible fouling in SA filtration is the most serious,and the calculated irreversible resistance reaches 3.77E+12m-1,while the filtration time to reach the stable stage is the shortest.The degree of irreversible pollution caused by the four membrane foulants is SA>MFs>BSA>HA from large to small.Secondly,based on Zeta potential monitoring of membrane fouling,the real-time characterization of cake thick:ness and density in membrane filtration process was carried out by using UTDR.It can not only effectively monitor the formation and growth of contaminated layer with UTDR,but also characterize the density change of contaminated layer by the change of differential signal amplitude.In this study,the synergistic relationship between the ultrasonic echo signal and the thickness of the cake layer were used to determine the time when the membrane filtration entered the compaction stage of the cake layer.The on-line monitoring method of Zeta potential combined with UTDR technology makes up for their shortcomings,and is more conducive to understanding the characteristics of membrane fouling process in the in-situ monitoring process.The results show that the time required for the four foulants to enter the formation and compaction stage of cake layer is SA>MFs>BSA>HA from fast to slow.Ultrasound differential signals were used to calculate the final thickness of the contaminated layer from thick to thin in order of HA,BSA,MFs and S A.According to XDLVO theory calculation,the interaction force between membrane-SA and SA-SA is greater than that between other foulants and membrane and each other.The adsorption rate of SA on membrane surface is faster in the process of membrane fouling,and it is easier to be compacted because of its relatively strong interaction force.The cake layer formed by SA filtration is also the thinnest according to the calculation of ultrasonic reflection data.The above work is of great significance for scientifically identifying the changing stages and selecting the best control opportunity to membrane fouling.