Research On Performance And Mechanism Of Nanofiltration Separating Natural Organic Matter From Water

Natural organic matter (NOM) is commonly found in surface and ground water andconsidered to react with the major disinfectants to produce a host of disinfection by-products(DBPs). Therefore, the removal of NOM effectively is of significant importance in meetingthe stringent DBPs regulations and providing safe drinking water. Nanofiltration (NF) allowsthe removal of dissolved organic matter. It has proved to be one of the best alternativesreplacing conventional drinking water treatment technologies and is increasingly used indrinking water treatment. Membrane fouling problems in the process of separationperformance of NOM by nanofiltration membrane remain to be further researched.The humic acid(HA), tannic acid(TA) and fulvic acid(FA) and tap water were tested forthe study in order to the comparisons of nanofiltration membrane retention on NOM,membrane flux decline, membrane adsorption, molecule weight distribution of water in andout of the membrane unit, and the analysis of inorganic ions’ influence on retention of NOMin drinking water by nanofiltration membrane. This study aims to analyze the mechanism ofremoving NOM by nanofiltration. The results of the study are as follows:(1) In the HA, chelating reaction between Ca2+and HA plays a main role. It producesmany polymers with complex structure characteristics, which are adsorbed on the membranesurface forming loose filter cake layer that has good permeability and slows the membranefouling effectively. At the same time, the complexation reaction between Ca2+and HA and"salt bridge" role of Ca2+improve the HA removal effect that reaches77.8%. Based on thecharge neutralization, HA removal rate increases by Na+, but the effect is not obvious.(2)In the TA, aqueous solution has half-colloidal solution properties; And TA itself is anatural macromolecular polysaccharide with big volume so that its flocculation can settledown from the water and precipitate or scale on the membrane surface, which can causesevere membrane flux decline. Its removal efficiency is general, maybe, because TA with lowmolecular weight molecules in water also accounts for the proportion. (3)In the FA, removal rate by NF membrane is very low because only part of the smallmolecules adsorb on the membrane pores. But that induces the membrane flux declineobviously.(4) Compared with NF experiments of each water sample, the tap water experimentfound that hydrophilic and part of hydrophobic components in tap water could formmembrane fouling, cause serious flux and retention decline, which is the focus ofnanofiltration process in tap water in future.