Characteristics Of Immersed Ultrafiltration Membrane Fouling Caused By Clay Particle And Organic Matter In Dringking Water Treatment

This paper was mainly conducted in laboratorary to study the characteristics ofimmersed ultrafiltration (UF) membrane fouling caused by clay particle and organicmatter in source water and investigate the influence of pretreatment, such as coagulation,adsorption of powdered activated carbon (PAC), coagulation-PAC on different type ofmembrane fouling (including total membrane fouling, reversible membrane fouling andirreversible membrane fouling). Based on the experimental filtration study, a morecomprehensive understanding of membrane fouling and the control mechnism wereobtained by the analysis of the molecular weight (MW) distributions of organic, XADresin fractionation, and scanning electron microscope (SEM), X-ray energy dispersivespectra (EDS), fourier transform infrared spectroscopy (FTIR) and fluorescenceexcitation-emission matrix (FEEM).The membrane fouling caused by organic matter is mainly irreversible. It includesfour courses of the membrane specific flux as quickly decline, the short-term steady,the smooth decline and increase after the backwash. The decline rate of membranespecific flux has an exponential relationship with TOC of source water in ultrafiltrationof organic matter: y=0.0157e0.0588x. The irreversible fouling caused by organic matteris mainly due to the narrowed membrane pore at the beginning of the filtration. Theirreversible fouling increased lineally with filtration time in the study.The membrane fouling caused by clay particle is mainly reversible due to cakelayer formation on the membrane surface. Experimental results demonstrate positivecorrelation between the turbidity of source water and the decrease rate of membranespecific flux. The predominant resistance was the cake resistance, which could beminimized by increasing the frequency of backwashing. The immersed hollow fiber UFmembrane could endure the mixture in membrane tank with turbidity below40000NTU. The existence of clay particle in the HA solution was found to be able to mitigatethe irreversible fouling caused by organic matter. However, the total membrane foulingby organic matter was increased. The SEM imagines demonstrated that cake layerformed by clay particle could prevent organics into the membrane pore hole andincreased the porosity of membrane surface, which greatly decreased irreversiblefouling. Coagulation pretreatment effectively decreased the total membrane fouling and theirreversible membrane fouling caused by organic matter. The irreversible membranefouling by organic matter was decreased by selecting appropriate operation parameters,such as coagulation retention time, dosage of coagulant, aeration strength, backwashingperiod and continuous dosing of coagulant.PAC pretreatment decreased the irreversible membrane fouling and increased thetotal membrane fouling caused by organic matter. Batch dosing of PAC was better andmore suitable for engineering application over continuous dosing. The combined effectof coagulant and PAC on irreversible membrane fouling was not the simple addition ofthe individual's effect, but less than the sum of the individual's effect. Addition ofcoagulant and PAC improved the structure of fouling layer on the membrane surface,declined the degree of membrane pore narrowed by organic matter at the early stage ofultrafiltration, which is the key reason to mitigate the irreversible membrane fouling byorganic matter.Regular chemical cleaning for removal of irreversible membrane fouling was alsoinvestigated with sodium hydroxide, hydrochloric acid and citric acid in this paper.The research results above would provide any insight into the characteristics ofimmersed ultrafiltration membrane fouling and the control mechanism in dringkingwater treatment.