Role of micro-size zero valence iron as particle electrodes in a three-dimensional heterogeneous electro-ozonation process for nitrobenzene degradation

A novel water treatment process (designated E-Fe0-O3 process) was constructed by combining electrolysis, micro-size zero valence iron (Fe0) and ozone in this study. Compared with other control processes, the combined process demonstrated a remarkable synergy, and it could obtain 90.5% of NB removal within 20 min. As for the mineralization experiment, the TOC removal efficiency for NB within 120 min was higher in the E-Fe0-O3 process, while the energy consumption was lower than the traditional E-O3 and E-Fe0 process. Interestingly, hydroxyl radicals (OH) acted as a key role for NB removal, and the concentration of OH in different processes were compared. Further study indicated OH, direct anode oxidation, direct ozonation, and zero valence iron catalysis were all responsible for nitrobenzene removal. Besides, the durability of Fe0 in the E-Fe0-O3 process was systematically evaluated by reusing Fe0 10 times. Notably, the electric field could protect micro-size zero valence iron from passivation for catalytic ozonation after the long-term reaction. Finally, other ozone-refractory organics pollutants were also investigated in the E-Fe0-O3 process, and the influence of various water matrices on NB removal was discussed. All results demonstrated that the E-Fe0-O3 process was an efficient method to remove refractory organic pollutants in various natural waters.