Influence of NOM composition on nanofiltration

Tar river water was used either in a natural organic matter (NOM) fractionation procedure or after pre-treatment with powdered activated carbon (PAC), in bench scale nanofiltration studies. Hydrophilic and hydrophobic fractions of NOM were prepared from reverse osmosis concentrated water. Effects of NOM composition on nanofiltration were studied by pre-adsorption of concentrated solutions onto PAC. Hollow fibre nanofilters of negatively charged polysulphone were used in batch recycle experiments. Average molecular weight distributions and TOC rejection during nanofiltration of hydrophilic, hydrophobic and unfractionated NOM are presented. Permeate flux over time and in response to membrane cleaning are depicted. TOC rejection and permeate flux during nanofiltration of PAC pre-treated and untreated NOM solutions are depicted. Hydrophobic NOM was responsible for nearly all permeate flux decline and was more highly rejected than hydrophilic NOM. NOM in solution after PAC treatment caused greater permeate flux decline and was more poorly rejected than the original NOM solution. NOM recovered from the membrane after nanofiltration generally had a molecular weight greater than 30,000 daltons.