With the recent emergence of hexavalent chromium (CrO4
2-) and perchlorate (ClO4
-)
contamination, and natural arsenate (H2AsO4
-/HAsO4
2-) occurrence as an important
drinking water quality issue, a careful assessment of membrane technology for trace
anionic contaminants removal was performed.
A bench-scale cross-flow flat-sheet filtration unit was used to evaluate short-term
(CrO4
2-, ClO4
-, and H2AsO4
-/HAsO4
2-) rejection by reverse osmosis (RO), nanofiltration (NF), and tight ultrafiltration (UF)
membranes, and a diffusion cell testing unit is being used to investigate anion transport
(by hindered diffusion) through membrane pores.
Several membrane studies have been performed to evaluate removal of anions that
are physically and chemically similar (e.g., molecular mass cut off (MMCO) and
electrostatic interaction by charge) to these three toxic anions.
In this study, RO, NF and tight UF membranes have been tested to evaluate the
effects of pH, conductivity (ionic strength), and mono- or divalent co- and counter ions
on the transport/rejection of these three toxic anions. This study investigated the transport
(rejection) mechanisms of CrO4
2-, ClO4
-, and H2AsO4
-/HAsO4
2- including solution
diffusion, steric (size) exclusion, and/or electrostatic exclusion for RO, NF and tight UF
membranes.
The target anions have been characterized according to molecular mass, hydrated
ionic radius (size), and diffusion coefficient in water (Dw). A diffusion cell with actual
RO, NF, and tight UF membrane specimens was 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 7 references, tables, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 240 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 9 |
| Published : | 03/05/2003 |
