AWWA MTC53867

In recent years, nanofiltration (NF) has been proven to be a viable option for disinfectionbyproduct (DBP) precursor control. Because DBP precursor rejection is a complexfunction of physicochemical interactions between natural organic matter (NOM) andmembranes, understanding the behavior of neutral compounds such as polyethyleneglycol (PEG) will be an important first step in elucidating organics rejection. StudyingPEG rejection characteristics will also help in establishing a baseline rejection usingneutral linear compounds to better understand NOM-membrane interactions. Molecular weight cut off (MWCO) is a commonparameter to specify ultrafiltration and nanofiltration membranes employed for organicsremoval. However, its determination has not yet been standardized leading to muchconfusion in membrane implementation and comparison of results from various studies.Concentration polarization is the phenomenon when solutes tend to accumulate near themembrane. This changes the observed rejection from its "true" value. The truerejection directly depends upon the gel concentration; hence obtaining an accurate valueof the gel layer concentration is important to calculate the true rejection. Twoapproaches usually employed to calculate the true rejection are the gel layer model andthe osmotic pressure model.Although, much work has been done using both models to calculate gel layerconcentration, there has been no direct comparison of these models to ourknowledge. The objective of this paper is to delineate the effect of various processvariables on concentration polarization and its implication on MWCO determination.To this end, cross flow experiments were conducted at constant flux. Includes 13 references, figure.