The evaluation on concentration polarization for effective monitoring of membrane fouling in seawater reverse osmosis membrane system

초록

One of the critical issues for the successful application of seawater reverse osmosis (SWRO) in the desalination processes is membrane fouling. However, it is difficult to evaluate fouling by the flux decline since recently commercialized SWRO membranes have better permeability than the initial membranes and the two-way coupling between salt concentration polarization and fouling influences permeate flux. In this study, we evaluated membrane performance using various factors, namely the permeation coefficient (L<inf>p</inf>) and concentration polarization factor (f<inf>cp</inf>). The values of L<inf>p</inf> and f<inf>cp</inf> were obtained according to the changing conditions of feed water total dissolved solids (TDS) concentration and operating pressure. As a result, L<inf>p</inf> and f<inf>cp</inf> increased with increasing operating pressure at the same feed water TDS, on the other hand, they decreased with increasing feed water TDS at the same operating pressure. The reasons for these results are that concentration polarization is enhanced with increasing operating pressure at the same feed water TDS and concentration polarization is weakened with increasing feed water TDS concentration due to osmotic pressure at the same operating pressure. Based on these factors and the equation combined with osmotic cake filtration theory and thermodynamic model, we could calculate the resistance by NaCl (R<inf>cp</inf>), which is constant with time like membrane resistance (R<inf>m</inf>). Thus, we would identify the fouling rate through fouling resistance (R<inf>c</inf>) by calculating L<inf>p</inf> and f<inf>cp</inf> according to time after spiking organic foulants. © 2013 The Korean Society of Industrial and Engineering Chemistry.

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