Bipolar Oxidative Technique Of Electrolysis Promoted By Ozone

As two environment-friendly oxidation technologies, electrochemical oxidation and ozonation have been mainly concerned by environmental researchers. However, due to the limit of the electrolytic potential of water and the selectivity of oxidative power of ozone, the two oxidative techniques have some shortcomings: low efficiency of organic degradation; uncomplete removal of organic. On the basis of this fact, the oxidative efficiency and the kinetic mechanism of the electrolysis coupled ozonation (electrolysis-ozonation) system was discussed in this paper, the aim of this work is to establish an oxidative system with high efficiencies for different organics degradation.The oxidative system of electrolysis-ozonation in an undivided cell was used to degrade nitrobenzene (NB) in the first; its kinetic characteristics and degradation mechanism were discussed. The experimental results indicated that the electrolysis-ozonation system had a significant synergistic effect during degradation of NB, and the system complied with the mechanism of hydroxyl radicals'oxidation. For example, the electrolysis-ozonation had a NB removal rate of 96.4% under the optimal conditions, while electrolysis alone plus ozonation alone only had the NB removal rate of 62.1%. In addition, the results of degradation of 4-chlorophenol (4-CP), oxalic acid (OA), acetic acid (HAC) by electrolysis-ozonation all showed high degradation efficiencies, indicating that the oxidative system had a good prospect for application in wastewater treatment.The oxidative efficiency of the anodic compartment in a divided cell was discussed to elucidate its role in this system. The experimental results of degradation of OA, HAC and NB revealed that the anodic compartment had some certain synergistic effect, but not very obvious. The above results probably inidicate that the synergistic efficiency of the anodic compartment of electrolysis-ozonation might attribute to free radicals generating at anodic surface, which initate the decomposition of ozone to produce hydroxyl radicals.The oxidative efficiency of the cathodic compartment in a divided cell was investigeated to elucidate its role in this system. The experimental results confirmed the high synergistic effect in NB degradation, indicating that the cathodic compartment played a main role for electrolysis-ozonation. For example, the removal rate of NB by electrolysis-ozonation was up to 99.2% in 600 s, however, only 58.2% for electrolysis alone plus ozonation alone under the same conditions. On the basis of the results of kinetic analysis, the synergistic mechanism of the cathodic compartment of electrolysis-ozonation might include three factors: (1) production of·O3- at cathode surface, (2) high pH value near the cathode, (3) H₂O₂ generation from electroreduction of dissolved oxygen. After calculation, the approximate proportions of three ways for NB degradation were 59.3 %, 29.5% and 11.2%, respectively.