Efficient degradation of emerging pollutant-malachite green in water by pulsed discharge plasma on water surface in cooperation with Fe/PMS.

The effective and rapid treatment of emerging pollutants in water is an essential solution to the pollution of water environment. The emerging pollutant-malachite green (MG) wastewater was treated using pulsed discharge plasma on water surface system (WSP) combining Fe/PMS. Compared with WSP alone, the addition of 125 μM Fe and 0.5 mM peroxymonosulfate (PMS) in WSP could enhance the degradation efficiency and energy efficiency of MG by 32.8% and 9.7% respectively, with the synergistic factor of up to 2.056. UV-Vis absorption spectra and mineralization further demonstrated the synergistic effect. When the peak voltage and air flow rate were 22 kV and 0.7 L/min, the degradation efficiency and kinetic constant of MG could reach 97.9% and 0.259 min, respectively. MG degradation with high conductivity (1000 μS/cm) by WSP + Fe/PMS not only exhibited the better purification effect, but also could maintain the faster reaction rate. The active species involved in the degradation of MG in WSP + Fe/PMS system were mainly ·OH, SO·, O· and e*. Furthermore, HO and O also have a certain oxidizing effect on MG. Cl, SO, HCO and humic acid (HA) could inhibit MG degradation to some extent, but still removed more than 80% of MG in water. The WSP + Fe/PMS reaction system was suitable for the treatment of other emerging pollutants in water. The results of LC-MS analysis revealed that the N-demethylation reaction and decomposition of conjugated structure were the important pathways for MG degradation. The HO and acidic liquid environment provided by WSP laid the foundation for the formation of Fenton, and the introduced Fe could fully undergo the Fenton and activation reaction with HO and a small amount of PMS in the liquid phase, which enhanced the generation of active species, especially ·OH.