Synergies of the Direct Electrochemical Reduction and Pd-Catalyzed Hydrogenation in a Sequential Membrane for an Efficient N-Nitrosodimethylamine Removal

Abstract

Rapid and economic removal of N-nitrosodimethylamine (NDMA) calls for advanced treatment strategies due to its mutagenic and carcinogenic effects, small molecular size, high polarity, and uncharged properties. Herein, a sequential Pd-modified polymeric ultrafiltration (UF) membrane coated on a carbon paper substrate (CpPdM) was designed for the complete elimination of NMDA in one single pass with low energy consumption, with the synergetic processes of direct electrochemical reduction and Pd-catalyzed hydrogenation. The hydrogen gas, produced from direct electrochemical reduction, could trigger the Pd-catalyzed hydrogeneration to improve the NDMA destruction performance. In addition, the pre-rejection of interfering substances in the water matrix by the frontmost UF layer hugely mitigates the fouling issues on the electrode, thus improving the stability. Moreover, the flow-through operation mode overcame the mass transfer limitation of traditional electrodes in the flow-by mode (100% NDMA removal within 12.6 s of residence time at −2.3 V), resulting in 2 orders of magnitude enhancement in modified reaction kinetics. Furthermore, the combined treatment of the CpPdM and nanofiltration was superior to the conventional reverse osmosis process in NDMA removal and energy use. This work is expected to provide a new strategy for developing an energy-efficient advanced wastewater treatment system.