Systematic Bench‐Scale Assessment of Perchlorate (ClO₄⁻) Rejection Mechanisms by Nanofiltration and Ultrafiltration Membranes

Abstract

Measurements of the rejection of perchlorate anion (ClO₄ ⁻) have been performed by using two thin‐film composite nanofiltration (NF) membranes and four ultrafiltration (UF) membranes. The latter four membranes are all from the same manufacturer and, ostensibly, from the same material family. These were chosen to systematically change the membranes steric properties, while keeping the same material chemistry, thus, the enthalpic interactions should stay constant. The perchlorate anion (at a concentration of 100 g/L of ClO₄ ⁻ by “spiking” with KClO₄) was presented to the membrane as a pure component, in binary mixtures with other salts, and at varying pH and ionic strength (conductivity). Also, a natural source water was “spiked” with perchlorate anion and used to document the effects of a complex mixture, including natural organic matter, on the observed rejection. All filtration measurements were performed at approximately the same permeate flow rate to minimize artifacts from mass transfer at the membrane interface. In general, the results indicate that, in a pure component system, target ions (in this case ClO₄ ⁻) can be significantly excluded from like‐charged membranes with pores large with respect to the size of the ion, but this rejection capability decreases in the presence of a sufficient amount of other ions that can screen the electrostatic force field.

^#Contribution of the US Government, not subject to copyright in the United States

Keywords:

• Nanofiltration
• Perchlorate
• Ultrafiltration
• Water treatment

Acknowledgments

The authors wish to acknowledge the American Water Works Association Research Foundation (Ms. Traci Case, project manager) for support of this project and Namguk Her for doing the FTIR measurements.

Notes

^#Contribution of the US Government, not subject to copyright in the United States

^aElectrokinetic Apparatus‐EKA, Brookhaven Instruments Corp., Holtsville, NY.

^bMilli‐Q, Millpore Water Purification System, Bedford, MA.

^cSEPA, Osmonics, Minnetonka, MN.

^dWe don't expect any artifacts in our measurements of ion flux due to bacterial growth because we used either synthetic water solutions prepared from DOC‐free water that was stored in bleach‐sterilized, covered containers, or CRW that was prefiltered with a 0.45 µm filter before the tests.

^eDX300 Ion Chromatography System including a CDM‐2 conductivity detector, a GPMII gradient pump, and an auto‐sampler. Dionex Corp., Sunnyvale, CA.

^fManufacturer's identification is required to provide an accurate description of the instruments used for scientific purposes only. Identification is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to imply that the equipment/materials used are the best available for the purpose.

^gLiberty‐Series II, Varian, Australia.

^hSigma, St. Louis, MO.

ⁱTOC‐5000, Shimadzu, Columbia, MD.

^jMagna‐IR750 Spectrometer Series II, Nicolet Analytical Inst. Corp., Madison, WI.