Multispectral Analysis Of Microfiltration Membrane Fouling Process In Water Treatment

Water is the source of life,and the shortage of water resources and serious water pollution problems lead to water crisis,which is a severe problem that restricts China’s social and economic development.An important way to alleviate the water crisis is the recycling and utilization of sewage.Membrane water treatment is a new high-efficiency wastewater treatment and reuse technology,which has the advantages of strong treatment capacity and good effluent quality,and has been widely used.Among the pressure-driven membrane separation technologies,microfiltration(MF)technology is the earliest research and the most widely used separation membrane.The research on microfiltration membrane fouling has been more than20 years.Membrane fouling is an inevitable and challenging problem in the process of microfiltration,which restricts the further popularization and application of membrane technology.However,membrane fouling is difficult to overcome because it is a dynamic and complex process.The main organic foulants,such as polysaccharide,humus and protein,are considered to be the main substances causing membrane fouling,and participate in different stages of the dynamic evolution of membrane fouling.In the initial stage of membrane fouling,the adsorption/blockage of membrane pores is mainly caused by membrane-foulant interaction,and in the later stage,foulants deposit on the membrane surface to form gel/filter cake,which is transformed into foulant-foulant interaction.Therefore,in order to control and prevent membrane fouling,it is necessary to understand the mechanism of membrane fouling,accurately describe the evolution process of membrane fouling,the changes of various organic components in the evolution of fouling and the evolution law of the interaction between membrane and foulants.Molecular spectroscopy is an effective means to solve the mystery of complex membrane fouling.In this paper,polysaccharide,protein and humic acid were used as model foulants,and the model foulant solution with similar ratio to the supernatant of membrane bioreactor in municipal sewage treatment was prepared for fouling evolution test.By means of various spectroscopy detection techniques,various statistical analysis methods were used to deeply analyze the development process of membrane fouling and the evolution law of membranefoulant and foulant-foulant interaction in each stage.As for the mechanism of membrane fouling,(1)Based on various membrane fouling studies in previous literature,this study clearly summarizes and sorts out a large amount of information about this topic,and compiles the role of membrane-foulant and membrane fouling molecular interaction in MF organic fouling;(2)Based on the linear additivity of filtration volume under different fouling mechanisms,a simple and direct multiple linear regression model is proposed to describe the piecewise continuity of five pore blockage/cake filtration fouling mechanisms in the whole filtration process.The filter curve(flux and volume)of each time period is fitted,and the insignificant mechanism is screened out by stepwise regression,and the dominant mechanism of each time period is determined.Dubin-Watson(DW)autocorrelation test is used to prove the most reliable setting of the number and length of time periods.For the evolution of membrane fouling,(1)Two receptor models,non-negative constraint factor analysis(FA-NNC)and non-negative matrix factor analysis(NMF),were used to analyze the infrared spectrum of the membrane surface and analyze the main fouling sources and their contributions.The results provide a promising statistical method for understanding the interaction mechanism between foulants and membrane-foulant at the molecular level.(2)The dynamic process of membrane fouling is characterized by various spectroscopic measurements,and various statistical methods,such as non-negative linear least square fitting,variance decomposition analysis and redundancy analysis,are used as auxiliary analysis methods to analyze a variety of series spectra of the effluent from microfiltration membrane and the contaminated membrane surface,identify the evolution rules of various foulants in the process of membrane fouling and quantify their interactions,thus revealing the dynamic evolution process of membrane fouling more deeply.The results show that based on the Ultravioletvisible(UV-vis),fluorescence excitation-emission matrix(EEM),circular dichroism(CD)and other spectra of effluent,it can roughly identify which types of foulants appear in which fouling stage;Based on the infrared and Raman spectra of the membrane surface,infrared spectra can sensitively recognize protein and polysaccharide,and Raman spectra can recognize humic acid,which are complementary;Based on the infrared and Raman signals on the membrane surface,it can identify how the interaction of polysaccharide-protein-humus evolves in each stage.