A review on the application of ozonation to NF/RO concentrate for municipal wastewater reclamation

Nanofiltration (NF) and reverse osmosis (RO) technology have gained worldwide acceptance for reclamation of municipal wastewater due to their excellent efficiencies in rejecting a wide spectrum of organic pollutants, bacteria, dissolved organic matters and inorganic salts. However, the application of NF/RO process produces inevitably a large volume of concentrated waste stream (NF/RO concentrate), which is generally characterised by high levels of inorganic and organic substances, a low biodegradation and potential ecotoxicity. At present, one of the most significant concerns for this process is regarding the sustainable management of municipal NF/RO concentrate, due to a potentially serious threat to water receiving body. It should therefore be further disposed or treated by effective technologies such as ozonation in a cost-effective way, aiming to minimize the potential environmental risk associated with the presence of emerging micropollutants (ng L-1 mu g L-1). This paper provides an overview on the disposal of NF/RO concentrate from municipal wastewater by ozonation process. This is a first review to present entirely ozonation efficiency of NF/RO concentrate in terms of elimination of emerging micropollutants, degradation of organic matters, as well as toxicity assessment. In addition, ozone combining biological activated carbon (BAC) or other advanced oxidation processes (AOPs) is also discussed, aiming to further improve mineralization of ozone-recalcitrant substances in NF/RO concentrate. Finally, further research directions regarding the management of NF/RO concentrate are proposed.