A Resistance Model for Evaluating Interaction between Natural Organic Matter (NOM) and Membranes at Differenct Scales of Operation

Bureau of Reclamation; Denver CO.
University of Colorado; Boulder CO.
September 1999

Report #44 - Executive Summary -

This reseach evaluated and compared NOM fouling of membranes at different scales of operation. The approach of this research was to interpret NOM fouling in terms of NOM-membrane interactions. Two different sources of surface water and two different membranes were tested to provide variation in the intrinsic properties which affect NOM-membrane interactions. Each water-membrane combination was tested at three different scales of operation. Permeate flux declined through time and was attributed to the development of a NOM gel layer on the membrane surface.

A methematical-gel resistance model was developed to analyze the NOM-membrane interactions and compare the test results at different scales of operation. The model includes parameters related to properties of the NOM, membrane, and feedwater. NOM was characterized in terms of molecular weight (MW) distribution and aromatic structure. Measured feedwater properties include pH, conductivity, and concentration of dissolved organic carbon (DOC). Membranes were characterized in terms of molecular weight cutoff (MWCO) of the pores, surface charge, and hydrophobicity.

Application of the gel resistance model to the membrane test results indicates that properties of the NOM, membrane, and feedwater can be quantitatively related to NOM fouling and the resulting permeate flux decline at each scale of operation. These quantitative relationships were observed at different scales of testing; however, each scale of membrane operation imposes unique operating conditions that also influence the test results. The gel resistance model also provided a means for interpreting the differences in test results due to the operational differences between each scale of testing. The utility of the model lies in its potential use as a tool for predicting NOM fouling and membrane performance at larger scales of operation.