AWWA MTC61092 PDF

With the recent emergence of oxyanions chromate (HCrO₄^-/CrO₄^2-), arsenate (H₂AsO₄^-/HAsO₄^2-), and perchlorate (ClO₄^-); and their contamination and natural occurrence as an important drinking water quality issue, a careful assessment of membrane technology for trace inorganic contaminants removal has been performed. A bench-scale cross-flow flat-sheet filtration unit has been used to evaluate the transport (rejection) of mono-valent and/or divalent oxyanions (HCrO₄^-/CrO₄^2-, H₂AsO₄^-/HAsO₄^2-, and ClO₄^-) through negatively charged reverse osmosis (RO), nanofiltration (NF), and tight ultrafiltration (UF) membranes, and a diffusion cell testing unit has been used to investigate oxyanion transport (by hindered diffusion) through membrane pores under various water chemistry conditions. In this study, RO, NF and tight UF membranes have been tested to evaluate the effects of pH and conductivity (ionic strength) on the transport/rejection these three toxic oxyanions. The study investigated the transport (rejection) mechanisms of chromate, arsenate, and perchlorate including solution diffusion, steric (size) exclusion, and/or electrostatic exclusion for RO, NF and tight UF membranes. The target anions were characterized according to molecular mass, hydrated ionic radius (size), and diffusion coefficient in water (Dw). A diffusion cell containing actual RO, NF, and tight UF membrane specimens has been used to estimate hindered diffusion (Dp) embodying various solute-membrane interaction, with measured hindered diffusion coefficients several orders of magnitude less than corresponding diffusion coefficients in water, thus demonstrating the importance of electrostatic and steric hindrance in trace anion rejection. Includes 11 references, table, figures.

Edition :	Vol. - No.
File Size :	1 file , 420 KB
Note :	This product is unavailable in Ukraine, Russia, Belarus
Number of Pages :	12
Published :	03/01/2005