Study On EPS Protein Quantification And Membrane Fouling Mechanism In Membrane Bioreactor

Membrane fouling is an important limiting factor affecting the development of membrane bioreactors.Extracellular polymers are considered to be one of the main causes of membrane fouling.The identification and quantification of the composition of extracellular polymers is the basis for studying membrane fouling.In this paper,common methods for quantifying protein values in extracellular polymers in membrane bioreactors are compared and selected.Aiming at the presence of interfering substances,a protein precipitation pretreatment method is proposed to improve the accuracy of the quantitative method test.The effect of EPS in the MBR sludge mixture in actual operation on membrane pollution was investigated,and the following conclusions were obtained:The Modified Lowry method has the advantages of low linear range,high accuracy,and the test absorbance is less affected by the reaction time among Modified Lowry method,BCA method,and Bradford method.but it is significantly affected by the Ca²⁺,Mg²⁺,and reducing sugar in the EPS.The BCA method and Bradford method are less accurate than the improved Lowry method,but they have better anti-interference properties for Ca²⁺and Mg²⁺.In addition,the humic acid in EPS seriously affects the accuracy of the BCA method and Bradford method.Using SDC-TCA precipitation method to separate and purify the protein,it was found that when SDC=300 mg/L,TCA=20%m/w,the lysozyme,egg white protein,5,10,25,50 mg/L,The precipitation effect of BSA reaches 94.00%-108.08%.In addition,compared with the TCA precipitation method,the addition of SDC effectively improves the precipitation effect of TCA on low concentration?5 mg/L?protein.SDC-TCA precipitation pretreatment removes interfering substances,which significantly improves the test accuracy of the improved Lowry method.Soluble EPS is the main influencing factor in the early stage of membrane fouling.In the properties of sludge mixture,MLSS,zeta potential,viscosity,and sludge particle size are also significantly related to the resistance of the polluted layer.Partial correlation analysis shows that the concentration of bound EPS is also significantly related to the resistance of the polluted layer,that is,the higher the bound EPS,the easier it is to cause membrane fouling.EPS has significant correlation with SVI,zeta potential and viscosity in the properties of sludge mixed liquid.the concentration of polysaccharide,protein,humic acid and soluble EPS The resistance of the polluted layer after filtration was significantly correlated,and the polysaccharide/protein ratio had a significant positive correlation with the resistance of the polluted layer after soluble EPS filtration.The reason for the higher filtration resistance of the polluted layer of the anaerobic MBR sludge mixture can be attributed to the higher solubility EPS,viscosity,particle size,solubility EPS,and zeta potential in the anaerobic sludge.