Interests and limitations of nanofiltration for the removal of volatile organic compounds in drinking water production

Most of volatile organohalide compounds (HOVs) present in surface waters and ground waters are carcinogenic. In drinking water, they represent a danger for human health and are present in water resources. The objective of this study was to characterize the performances of nanofiltration as a refining step for removing these compounds at trace level in water. Three HOV compounds which are toxic and highly present in natural waters were selected: trichloroethylene, tetrachloroethylene and chloroform. Performances of different nanofiltration organic membranes to remove these compounds are presented. High rejection ratios were obtained. Influence of pressure on selectivity is low. Rejection mechanisms are discussed. Separation seems partially governed by steric effects, but another phenomenon was noticed and characterized: HOVs absorb, diffuse and then desorb from organic membranes. This phenomenon was especially observed for chloroform. As a consequence of desorption in the filtrate, the regulation limits for drinking water were not always reached. Moreover, some modifications of membrane properties were observed by chemical ageing tests.