Arsenic rejection by membrane processes: model development and application
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[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] This study investigated the rejection of arsenic by several nanofiltration and inorganic clay membranes. Laboratory-scale experiments were conducted using both dead-end and cross flow systems. Firstly, the nanofiltration membranes, NF270 and TFC-SR-2, were selected for arsenic rejection in dead-end stirred cell filtration equipment. The results showed that rejection rate of As(V) could be higher than 90%. A better arsenic removal was achieved by the As-GAC/TFC-SR2 hybrid membrane system. The rejections of As(V) were modeled using Donnan Steric Pore Model (DSPM) model. The Film theory was coupled for consideration of the concentration polarization. The extended Nernst-Planck equation was solved numerically using a fourth order Runge-Kutta method. The calculated rejections were in good agreement with the experimental results. Secondly, nanofiltration membranes, GE-DK and GE-DL, were applied in cross flow systems to evaluate their performance for arsenic rejection. The results were interpreted by calculating the contribution of convection, diffusion and electrostatic migration to arsenic transport through the membranes. The calculated results showed the importance of the contribution of diffusive transport at low flux, but its contribution to transport decreased with the increasing permeate flux. The electromigrative and convective flux arisen correspondingly. The increase of electromigration was more important and gradually significant to the overall arsenate transport.
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