Ozone oxidation of nanofiltration concentrates alleviates membrane fouling in drinking water industry

Nanofiltration is an attractive technology for the production of drinking water from surface water. However, membrane fouling, mainly caused by natural organic matter, increases the costs and limits the water recovery. In this study, it was investigated whether the decomposition of natural organic matter in the concentrate stream by O3, has a positive effect on the membrane flux of four nanofiltration membranes (NF 90, NF 270, Desal 51, NF-PES 10). The results show that O3 oxidation causes a significant alleviation of membrane fouling for all investigated membranes. This is caused by the selective removal of unsaturated bonds and hydrophobic components in the dissolved organic matter, and by the decomposition of molecular chains into smaller fragments by O3. However, the chemical oxygen demand could not be reduced by more than 20%. The performance of O3 + H2O2 was only slightly superior to O3 alone, using an identical O3 dose.

► The discharge of the concentrate stream limits the water recovery of nanofiltration. ► The effect of O3 oxidation on membrane fouling of the concentrate stream is studied. ► A significant increase of flux for 4 commercial membranes was observed. ► This is caused by the selective removal of hydrophobic unsaturated compounds by O3. ► The COD could not be reduced by more than 20%, even with the addition of H2O2.