Fouling Characteristics And Effect Of Pretreatments In Treating Dyeing Secondary Effluent By RO Membrane

Secondary effluent reuse after advanced treatment is an important measure to alleviate water resources shortage situation, but also an effective way to reduce water pollution. Reverse osmosis (RO) membrane technology has its advantages in secondary effluent reuse for its low energy consumption, non-pollution and low operating cost. However, membrane fouling formed by the complex secondary effluent substances will reduce the efficiency and effect of the RO membrane technology. This article mainly studied RO membrane fouling mechanism during filtration process, and the effect of a variety of pretreatment methods(soften, ion-exchange and ultrafiltration).(1) The thorough analysis showed that the dyeing secondary effluent after PAC flocculation was of high salt content and micro-hardness.The soluble organic matter (EfOM) was with the highest content of hydrophobic substances, wherein the hydrophobic acid content followed by a hydrophilic substances. Organic molecular weight distribution ranged in<1k (27.42%),1k-10k (33.97%),10k-100k (29.88%) and>100k(8.73%). Three-dimensional fluorescence analysis showed that the organic substances were mainly composed of polysaccharides, aromatic protein and humic acid, fulvic acids, in which protein content was more than polysaccharides.(2) RO membrane would be fouled seriously after membrane filtration directly by flocculation effluent. After40h of membrane filtration experiment, the membrane relative flux decreased by87.14%with poor reversibility. DOC and conductivity removal were changed from the initial99.96%and97.46%to94.88%and94.54%. The different membrane filtrations and fouled membrane surface analysis among pH8.65,7.65and5.89showed that membrane fouling included inorganic fouling, organic gel fouling and calcium-organic complexation fouling. Three-dimensional fluorescence, infrared analysis and quantitative determination of membrane surface contaminants showed that membrane organic pollutants mainly comprised of protein, polysaccharides and hydrophobic acid, which protein content was higher than polysaccharides.(3) By studying the effect of a variety of pretreatment methods on RO membrane fouling, we could conclud that membrane fouling would be reduced by62.07%after soften pretreatment, while the reversibility increased. Soften-magnetic resin and soften-UF could reduce membrane fouling effectively, and the former decreased membrane fouling from87.14%to15.23%while the latter decreased membrane fouling to15.60%. Magnetic resin preferentially removed protein and small organic molecules, while ultrafiltration preferentially removed polysaccharide. The former had a higher removal for both hydrophilic and hydrophobic substances compared with other fractions, while the latter had a higher removal for hydrophobic substances. Ultrafiltration (1kDa) had almost the same effect compared with magnetic resin(Q3), while ultrafiltration (10kDa) had almost the same effect compared with magnetic resin (Q1). After the ultrafiltration pretreatment, the membrane fouling content was primary of protein, while after magnetic resin pretreatment,the membrane fouling content was primary of polysaccharides.