| Recently, electrochemical oxidation for the toxic organic wastewater treatment has attracted great attention due to its high treatment efficiency and ease of operation. However, previous researches on electorchemical reactor concentrated more on electrode material, while the research of the reactor and its structure optimization were rarely studied. Besides, the tubular electrochemical reactor （also named as Plug-flow Electrochemical Reactor （PFER）） has been widely used in organic wastewater treatment and it has the advantages of high degradation rate for pollutants and ratio of electrode to wastewater. In this study, we designed a novel plug flow electrochemical reactor with multi-rotating electrodes. It can enhance the disturbance intensity located nearby the electrode surface, which can further enhance the mass transfer of the process of electrochemical oxidation, and then the surface renewrate of electrode surfacewas accelerated. Therefore, the organic degradation rate of the electrochemical oxidation was enhanced. Main results are as follows:（1） In order to select the electrode material and the gap between electrodes, the related experiments were carried out in a batch electric tank for simplification, using the phenol-wastewater as the degradation system. Results revealed that the mesh structure of the anode favors better phenol removal efficiency as compared to that of the plate structure. Concerning the electrode material, the phenol removal efficiency of the Ti/PbO2 anode was significantly higher than that of Ti/IrO2-RuO2 and Ti/RuO2-Ta2O5 due to the high oxygen-evolution potential. In addition, the smaller gap between electrodes needs the lower tank voltage, which was beneficial to the phenol removal efficiency. In this study, considering the security of the rotating electrode, the gap between electrodes was set as 20 mm. According to the mentioned researches, a novel multi-rotating-electrodes plug-flow electrochemical reactor （MRE-PFER） was developed.（2） Effects of the structural and operation parameters on the fluid residence time distribution （RTD） were investigated by the tracer pulse-input method. Results demonstrated that the lesser flow back-mixing was obtained at the mode of radial feed and the increase of feed flowrates. In addition, the rotating speed of electrodes had a significant influence on the flowing conditions when small feed flowrates was employed. The back-mixing of the reactor is reduced with the increasing of the rotating speeds at the beginning. However, when the rotating speed was above 100 rpm, the back-mixing was aggravated.（3） The influence of processing and operating parameters on phenol removal efficiency was studied by using the phenol wastewater system. Results indicated that the optimal processing parameters in the experimental range are as follows:the initial value of pH, the concentration of supporting electrolyte, and the current density were less than 9.0,10 mg·L-1, and 15 mA· cm-2, respectively. Besides, the optimal operating parameters were attained with the conditions of 100 rpm for the anode rotational speed. However, the circular flow rates have a little effect on the phenol removal efficiency, and 60 L·h flow rate was employed in this work. Additionally, the biodegradability of phenol wastewater which was degraded in the optimal condition was also investigated. Results proved that the biodegradability was improved significantly when the electrolytic time is 120 min.（4） The phenol concentration in the MRE-PFER along the axial distance was analyzed. Based on the experimental data, the equation of phenol concentration in the MRE-PFER changed with time was obtained. It can also found that the phenol degradation followed the first-order kinetics model and the reaction rate constant is 0.01303min-1. Furthermore, the mass transfer coefficient km was equal to 1.611×10-5 m·s-1 when the anode rotational speed was 100 rpm, which was 1.42 times than that of the anode rotational speed was 0 rpm. It can be concluded that the mass transfer performance of rotating electrode electrochemical reactor was apparently enhanced as compared to that of the traditional electrode with the stillness anode. |
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