Standardized membrane pore size characterization by polyethylene glycol rejection

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 size distribution 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 specialized knowledge. 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 35,000 daltons. 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.