Research On Membrane Fouling Behavior Based On In-situ Online Monitoring Technology

The hollow fiber ultrafiltration membrane has been widely applied in water treatment industry,however,the membrane fouling impacts filtration efficiency.In constant flux process,due to the existence of pressure gradient,the fouling propensity of hollow fiber membranes varies along with the axis direction,which have a decisive influence on the performance of the membrane process.In this work,the local membrane fouling behaviors and membrane fouling migration are investigated by using electrical impedance and zeta potential.Then,the different fouling stage such as pore blocking,cake layer formation and cake layer compaction were redefined,and the influence of membrane fiber length and operating flux on membrane fouling migration to determine the effective filtration and the best operating flux.We can draw the following conclusion:1.As the results shown,both the El and ZP can be employed as indicators of the membrane fouling mechanisms.In the initial stage,the TMP,El and ZP increase rapidly due to the rapid absorbance of foulants in the membrane pores and on the membrane surface,which can be defined as the process of pore blocking.In the medium stage,the TMP,El and ZP increase gradually as the concentration enhanced cake layer fouling which can be known as the cake layer formation.Finally,the El decreases,while both TMP and ZP are relatively stable which could be defined as the cake layer compaction.2.Using the same analyzing method,it existed the non-uniform fouling distribution i.e the fouling of outlet was most serious,followed by the middle,finally the end on the axial direction during the constant flux dead-end filtration of 0.5 g/L mixture of yeast and kaolin,and it also existed the difference of fouling proceedings i.e the outlet was always the first to enter the cake layer compaction,followed by the middle,finally the end on the time.3.In the late filtration stage,it occurred the membrane fouling migration due to the redistribution of membrane fouling during the constant flux dead-end filtration mode of 5 g/L mixture of yeast and kaolin.Membrane fouling migration was defined as the phenomenon of redistribution of membrane fouling at the different locations of the axial direction during the constant flux dead-end filtration system of hollow fiber membrane.4.With the same operating condition,the influence of fiber length on membrane fouling migration was studied.As the results shown,the non-uniform fouling distribution at different locations of axial direction was obvious and the membrane fouling distribution occurred rapidly when the fiber was shorter.When the fiber was longer,the non-uniform fouling was not obvious and no fouling migration occurred.Moreover,the end of membrane fiber became an inefficient filtration part leading to the reduce of filtration efficiency due to the serious lace of suction force.At the same time,it is also analyzed the influence of different operating flux on membrane fouling migration.With the operating condition of sub-critical flux,there was no phenomenon of membrane fouling migration.With the operating condition of critical flux,membrane fouling migration would occur due to the redistribution of membrane fouling.With the operating condition of super-critical flux,the non-uniform fouling was the most obvious,and the membrane fouling migration would occur two times.