| Azo dyes are the most abundant and versatile class of synthetic dyes in the textile, printing, plastics, leather and food industry. However, the dye-containing wastewater is recalcitrant to degrade due to its intensive color, heavy concentration of COD, strong toxicity and complex organic ingredients. Discharge of wastewaters containing dye may cause a serious water environmental hazard and public health concern if improper handling. Various physical-chemical and biological methods have been used to remove color from dye containing effluents, but there are still some challenges for balancement between high efficiency and low cost. In recent years, Microbial electrolysis cell(MEC) has been explored extensively to reductively transform several refractory substance into less toxic forms based on cathode reduction reaction. The paper aims to investigate the feasibility of titanium suboxide(Ti Ox) serving as cathode for decolorization of Acid Red B(ARB, used as a model azo dye) compared with traditional carbon cloth in a two chamber MEC system.The MECs with carbon cloth cathode and Ti Ox cathode were constructed successfully and then we analyzed the the performance of different cathodes on ARB decolorization. During startup period, anodic electrochemically active microorganisms adapted well in MECs system, the anodic potential came to-450 m V and the cathodic potential remained about-950 m V. ARB decolorization kinetics could be fitted to a first-order logarithmic decay model for both carbon cloth cathode and Ti Ox cathode. The kinetic coefficient for Ti Ox was 0.339 h-1, which was 92.6 % higher than that for carbon cloth(0.176 h-1). The ARB decolorization efficiency with Ti Ox cathode achieved 91.95% within 7 hours, while the carbon cloth cathode need more than 12 hours to achieve similar results, demonstrating that the Ti Ox cathode accelerated the reaction kinetic process significantly. A possible cathodic reaction mechanism for the removal of ARB was suggested based on the reduction products identified: the azo bond of ARB was cleaved at the cathode, resulting in the formation of 1-naphthylamine-4-sulfonic acid and 2-amino-1-naphthol-4- sulfonic acid.Cyclic Voltammetry and Electrochemical Impedance Spectroscopy(EIS) were measured to investigate the electrochemical behavior of ARB on carbon cloth cathode and Ti Ox cathode. Cyclic Voltammetry demonstrated that the both cathodes could be used as electron donor for ARB decolorization. Charge transfer resistance(Rct), and diffusion resistance(Rdiff) of Ti Ox cathode was only 10Ω, 12Ω, which was much lower than that of carbon cloth cathode(588Ω,3411Ω), suggesting that the Ti Ox cathode was more favourable for electrons transfer from the cathode to ARB and promoted the mass transport process as the larger active surface area of porous Ti Ox.We also analyzed the key factors affecting ARB removal and performance of the MEC system with Ti Ox cathode. It turned out that when the initial concentration of ARB keeped below 400 mg/L, 0.5V was the optimal operating voltage, 7.0 was the optimal cathodic p H for MEC to fulfill shorter operation time, lower power consumption and higher Coulombic efficiency.Finally, we analyzed the electrochemical stability of Ti Ox cathode. The resuls showed that the corrosion current density of Ti Ox cathode increased slowly with the concentration increasing in acidic or chloride ions containing corrosive solution, indicating that Ti Ox cathode has a stronger resistance to corrosion to work in electrochemical environment. |
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