Nanofiltration concentrate treatment for increasing the water recovery in drinking water production

Nanofiltration is an attractive technology to treat surface water for the production of drinking water. Due to scaling and fouling of the membranes, the water recovery in nanofiltration is generally limited to about 80%. This paper presents the provisional results of a project that elaborates the concept where the membrane concentrates are treated, so they can return to the feed side of the membrane, without increased membrane fouling, in order to reduce the water loss. O3 oxidation of natural humic acid solutions showed that O3 is able to decompose the hydrophobic part of the organic matter, responsible for membrane fouling, very efficiently. However, it is not possible to achieve a high mineralization degree with pure O3 oxidation. The addition of H2O2 to the ozonated solution could slightly improve the mineralization degree. The salts in the concentrates are removed by electrodialysis. The membranes FTAM and FTCM of Fumatech were used for this purpose. The transport number of SO42- ions relative to Cl- ions was higher than 1, although steric hindrance typically obstructs the transport of SO42- ions through ion selective membranes. The change in permselectivity between monovalent and divalent ions makes these membranes very attractive for this application.status: publishe