Coagulation-ultrafiltration Cake Layer Porosity Determination By Ion Probe Method And Discussion Of Structure Influence

The coagulation-ultrafiltration process has attracted a lot of attention in drinking water treatment aera due to its convenient operation and excellent pollutant treatment performance.However,membrane fouling of pollutants orn the membrane during operation is a major problem that hinders the application of the process to industrialization.In this paper,a new method for measuring membrane fouling will be proposed to solve this problem,and the effects of different coagulants and hydraulic conditions on water treatment and membrane fouling porosity will be studied.Although there are many methods currently used to measure the porosity of the filter cake layer,they are limited in indirect processing because of indirect measurement.This study will develop a new test method for applying fluorescent probes to the filter cake porosity of conventional coagulation-ultrafiltration processes.In order to generate a fluorescent signal that can be received,quercetin and carbon quantum dots(CNDs)are used to excite the fluorescence of Al3+ ions and Fe3+ ions present in the coagulant to compensate for the conventional coagulation-ultrafiltration process.There is a defect in fluorescence.The adjusted coagulation strengths were 100 rpm,200 rpm,300 rpm and 400 rpm,respectively.Under the conditions of adding different coagulants(AICl3·6H2O and FeCl3·6H2O),different filter cake layers were obtained.The CLSM technique was combined with image analysis techniques to measure the porosity of the filter cake,and this result was statistically compared to the porosity calculated by the classical Carman-Kozeny formula using a t-test.The fitting degree of the two coagulant conditions and the calculated results can reach 95%and 98%,respectively.It is proved that the method of detecting the porosity of the filter cake layer by fluorescent ion probe has higher accuracy.In addition,under the same experimental conditions,the effects of coagulant type and stirring intensity on floc size,fractal dimension,removal efficiency of pollutants in water and degree of membrane fouling were analyzed.The size of the aluminum salt coagulated flocs is smaller than that of the iron salt coagulated flocs,both of which are the largest at 200 rpm and the smallest at 400 rpm.However,due to the different fractal dimensions,the aluminum salt floes are more compact overall.The iron salt floc structure is relatively loose.Aluminum salt coagulant has better removal effect on UV254 and TOC in water,but iron salt coagulant can reduce flux attenuation and slow down the accumulation of membrane fouling.The aluminum salt coagulant had the lowest membrane fouling degree at the stirring strength of 200 rpm,and the highest at 400 rpm.The iron salt coagulant had the lowest membrane fouling degree at the stirring strength of 100 rpm,and the highest at 200 rpm.Therefore,when different coagulants are added,the stirring strength should be appropriately changed to obtain an optimum treatment effect.The form of the complex formed by hydrolysis of the metal ion affects the porosity and the structure of the filter cake layer.In contrast,the aluminum salt coagulated filter cake has a small porosity and a compact structure;and the iron salt mixed filter cake The porosity is large and the structure is loose.Both the fractal dimension and the floc size have an effect on the filter cake layer,but the fractal dimension has a greater effect on the porosity than the floc size.