| The retention properties of an ultrafiltration (UF) membrane with 1000Da MWCO were investigated with bisphenol A (BPA) as a model hydrophobic solute in the presence of different electrolyte ions and over a wide pH range. The Stokes radius of the hydration molecule of the BPA was calculated with the hydrodynamic model by simulation of BPA transportation in the membrane. It was found that the rejection efficiencies of BP As visibly decrease in the presence of various ions (Na+, Li+, Mg2+, H+ and OH-). Simulation results showed that the effective radius of the hydration molecules was reduced accordingly. The lowering of the BPA rejection efficiency induced by ions followed the laws of Hofmeister series, i.e. Mg2+ > Li+ > Na+ and H+ > OH-. It is proposed that the added ions may compete water with BPA hydration molecules and cause the partial dehydration of them, which causes a decrease in the effective radius of the BPA molecules. This research helps to understand the effect of hydration and dehydration on the removal of hydrophobic emerging contaminants in a membrane with low MWCO.Fulvic acid (FA) is the main water-soluble component of the humic substances which is readily to cause membrane fouling for drinking water treatment. The aim of this study is to investigate the membrane fouling characteristics and mechanism caused by FA with the existence of different kinds of salt ions (Ca2+, Mg2+, K+ and Na+). A series of experiments were carried out to characterize the decline of membrane flux, rejection of the pollutants,FA aggregates, morphology of fouling layer on the membrane. Compared with the pure FA solution, the FA- monovalent ions (K+ and Na+) solution led to much lower membrane flux and membrane fouling which is hard to be recovered. In the presence of FA-divalent ions(Ca2+ and Mg2+) solution, the membrane flux increased obviously and the membrane fouling can be renewed easily. LPS analysis showed that the FA fromed larger aggregates in the presence of Ca2+ or Mg2+ ions. From analysis of AFM and SEM, it is proposed that monovalent ions may make the colloids to form the gel layer, which can lead to pore blocking and membrane flux decrease. While the divalent ions may react with fulvic and form cake layer with bigger particles on the membrane surface. Compared with gel layer,the cake layer is more porous and removed easily.The retention properties of single Bisphenol A (BPA) solutions and mixture of BPA/humic substance solutions using a regenerated cellulose acetate membrane were studied. The BPA rejection coefficient was found to increase with the increase of NOM concentration in the solution. It was found that the increase of the BPA rejection coefficients follows the number of hydrophobic groups, i.e. humic acid > fulvic acid. This phenomenon was attributed to the interaction of the similar structure of BPA molecules and humic substances surrounding the environment. While in the presence of electrolytes, the rejection of BPA is lower than before and higher than that of pure BPA solutions. This phenomenon can be attributed to the coagulation of FA and the partially dehydration of BPA, which is both due to the inorganic salt ions. In addition, BPA molecules could combine with unbonded hydrophobic groups arround the NOM and lead to a larger effective molecular size. |
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