Articulo Analitico

Standardized Membrane Pore Size Characterization by Polyethylene Glycol Rejection
Christopher T. Cleveland, M.ASCE1; Thomas F. Seacord, M.ASCE2; and Amy K. Zander3
Abstract: The objective of this research was to provide information toward standardization of a method for determining and describing the pore size distribution of ultrafiltration or nanofiltration membranes. Currently, pore sizedistribution testing is not standardized, making membrane selection to achieve treatment objectives difficult at best. The method utilized in this work provides a standard testing procedure as well as a pair of descriptors P 90 and the tightness coefficient that provide needed information about the membrane pore sizes and pore size distribution. The method requires minimal equipment and no specializedknowledge. Determination of both P 90 and the tightness coefficient allows direct comparison of mean pore size and pore size distribution of membranes on a standardized basis. The pore size distribution of three membranes was determined under varying solution and pressure conditions by measuring the solute rejection for various sizes of polyethylene glycol molecules in the range of 600 to 35,000daltons. The method can be replicated and the results are independent of the process variables of pressure and solution characteristics within the region likely to be encountered in drinking water treatment. DOI: 10.1061/ ASCE 0733-9372 2002 128:5 399 CE Database keywords: Pore size distribution; Water treatment; Membrane processes; Filtration.

Introduction
With the increasing application ofmembrane filtration in drinking water treatment, the complexity of the selection of appropriate membranes has also increased. As the number of choices for membrane systems increases, selection of membranes to pilot test for a particular treatment objective becomes more difficult. Having information available to describe these membranes in a form that is accurate, understandable, and uniform across allmanufacturers is key to informed decision making for membrane selection. As a result of new regulations enacted and proposed by the U.S. Environmental Protection Agency EPA , including the Disinfectant-Disinfection By-Product D/DBP Rule, much interest has been generated for alternative treatment technologies which have the potential to meet existing and anticipated regulaˆ ´ tions Laıne et al. 1993. Nanofiltration is one of the technologies that has gained attention for removal of organic compounds, which are a known DBP precursor. A significant amount of research has been performed in the area of nanofiltration, confirming its effectiveness in the removal of organic compounds e.g., Taylor et al. 1987; Fu et al. 1994; Allgeier and Summers 1995 .
Engineer, Carollo Engineers, 12592 West ExplorerDr., Suite 200, Boise, ID 83713. 2 Engineer, Carollo Engineers, 12592 West Explorer Dr., Suite 200, Boise, ID 83713. 3 Associate Professor, Dept. of Civil and Environmental Engineering, Clarkson Univ., Potsdam, NY 13699-5710. Note. Associate Editor: Peter Fox. Discussion open until October 1, 2002. Separate discussions must be submitted for individual papers. To extend the closing date by onemonth, a written request must be filed with the ASCE Managing Editor. The manuscript for this paper was submitted for review and possible publication on July 31, 2000; approved on October 25, 2001. This paper is part of the Journal of Environmental Engineering, Vol. 128, No. 5, May 1, 2002. ©ASCE, ISSN 0733-9372/ 2002/5-399– 407/$8.00 $.50 per page.
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With the nanofiltration market growing,manufacturers are eager to develop new membranes with ever-improving characteristics, responsive to industry needs. However, claims regarding low fouling potential, high permeability, and absolute rejection of particles equal to the rated pore size of the membranes are being questioned by researchers and regulating bodies, making it increasingly important to accurately determine these characteristics....