| It found that more than20countries have arsenic disease or high arsenic ward area. Exceeding50billion people are drinking the unsafe water which contains arsenic more than50μg/L. In2006, the Chinese government promulgated the new Standards for Drinking Water Quality(GB5749-2006)and set the maximum contaminant level(MCL) for arsenic at a tighter standard for10μg/L. However, there is a problem that the current cost of arsenic removal methods is high, considering that endemic arsenic toxicosis occurs mainly in the rural areas in our country. Therefore, there is an urgent need to develop new methods for arsenic removal from drinking water. In order to ensure stable water quality in the case of lower operating costs.This topic did research for the effect of complexometric-ultrafiltration technology for removing arsenic from drinking water. It made a membrane coagulation reactor (MCR) with ultrafiltration membrane. Replaced the traditional process of sedimentation, filtration and disinfection unit with membrane separation. MCR is an organic integration of membrane separation technology and coagulation reaction.The results showed that:arsenic removal efficiency ranged more than90%, and arsenic removal to low levels(<10μg/L)was achieved using a coagulant dose of5mg/L(calculated as Fe3+)when the concentration of arsenic in raw water was100μg/L. The remove mechanism mainly is:As(v) was adsorped by iron hydroxides generated from the Fe3+hydrolysis, There were surface functional groups=Fe-OH on iron hydroxides surface. Direct surface complexation between Fe-OH and As (V) occurred. And then removed by the ultrafiltration through membranemechanical sieving and the intercept effect among membrane and solute, solvent (including van der Waals forces, hydrogen bonding forces, and electrostatic forces).The research also showed that:pH of the raw water has significant effect on the As(V) removed by complexation-ultrafiltration technology. Arsenic removal efficiency ranged more than80%under neutral conditions (pH6to8). Then raise or lower the pH will affect the removal efficiency. The Cl-, NO3-, SO42-in the raw water made seldom effect on the As(V) removal by complexometric-ultrafiltration technology. While the existence of HCO3-and HPO42-will arrest the removal effect of As(V). Especially the HPO42-has more intense inhibition on it because of competitive adsorption with the AsO43-. The K+had no obvious effect on complexometric-ultrafiltration technology. While the presence of Ca2+,Mg2+increased the rate of arsenic removal, and the promotion of Ca2+to arsenic removal is more obvious than Mg2+. When the concentration of Ca2+in original water increased from1mmol/L to10mmol/L, the arsenic removal increased from83.8%to91.6%.Dynamic experiment study has shown that:MCR made the arsenic removal efficiency ranged more than90%. The arsenic concentration of effluent water was below the total arsenic criterion of Standards for Drinking Water Quality (GB5749-2006). Through the analysis of the ultrafiltration separation model and the flux value under different pressure penetration in the experiment, the model of the linear model was getted:y=1276.1x-0.26, R2=0.9920.Membrane fouling research showed that:Pure membrane resistance, concentration polarization resistance and the cake layer concentration more than half of the total resistance. But in the operation, they remained basically unchanged. The main reason for decline of membrane flux was the increasing of the membrane fouling resistance. The physical and chemical cleaning can made good effect. The membrane flux could recover to91.8%of the initial value after physical and chemical cleaning. In the early running, the membrane fouling was mainly caused by inorganic matters, with the reaction, organic pollution and irreversible contamination proportion gradually increased. |
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