Removal of N-nitrosamines in a membrane bioreactor and nanofiltration hybrid system for municipal wastewater reclamation: Process efficiency and mechanisms

• MWCO of NF membranes is a key factor affecting removal of bulk water contaminants.
• Reactivity of amine groups with catabolic enzymes determines removal of N-nitrosamines.
• Removal of N-nitrosamines by NF membranes can be mainly governed by size-exclusion.
• Adsorption onto membrane surfaces significantly contributes to removal of N-nitrosamines.
• Formation of membrane fouling may enhance removal of N-nitrosamines with low MW.

This study investigated the removal efficiency and mechanisms of water contaminants (mainly N-nitrosamines) during municipal wastewater reclamation by a membrane bioreactor (MBR) and nanofiltration (NF) hybrid system. The removal of bulk water contaminants was governed by the microbial activities in the MBR and molecular weight cut-off (MWCO) of the NF membranes. The removal of N-nitrosamines by the MBR was primarily attributed to biodegradation by aerobic bacteria, which can be determined by the reactivity of the amine functional groups with the catabolic enzymes (removal efficiency = 45–84%). Adsorption and formation of membrane fouling can enhance the removal of N-nitrosamines by the NF membranes. However, size-exclusion is found to play a major role in the removal of N-nitrosamines by the NF membranes since the removal efficiencies of N-nitrosamines varied significantly depending on molecular weight of the N-nitrosamines and MWCO of the NF membranes (removal efficiency: NE90 > NE70).