| The efficient removal of refractory organics from the industrial wastewater discharged by papermaking, printing and dyeing, chemical industry, pesticides and pharmaceuticals has been a hotspot and difficulty in water pollution control field recently. Since constructed wetland (CW) and microbial fuel cell (MFC) possess great potential in purification of refractory organics, therefore, this paper presented a novel constructed wetland-microbial fuel cell (CW-MFC) with combination of both structures. Simultaneously, bio-film electrode reactor (BER) was used as pre-treatment prior to CW-MFC, and the bioavailability of wastewater could be improved by the co-operative function of electrochemical action and biological process, then the removal efficiency of refractory organics and the electricity production performance in the CW-MFC were promoted. Moreover, electricity energy generated by CW-MFC was supplied to BER, and the BER/CW-MFC system achieved the exchange of substance and energy. In this study, azo dye reactive brilliant red X-3B (RBR X-3B) was used as the target of degradation, the dye decolorization efficiencies and influence factors by double cylindrical integrated BER and three-dimensional BER (3D BER) were investigated. Furthermore, a novel type of high-performance wicking granular activated carbon-stainless steel mesh (GAC-SSM) bio-cathode was developed for the CW-MFC, and operational parameters of CW-MFC were optimized. Finally, the removal effect of RBR X-3B by BER/CW-MFC coupled system was studied. Through the research of the thesis, the main results were obtained as follows:1) A new kind of double-cylindrical integrated BER with graphite rod as anode and activated carbon fiber attached to steel as cathode was constructed, the technical conditions for removing RBR X-3B by the BER were optimized, and the related dye degradation mechanisms were also discussed. Experimental results showed that when RBR X-3B concentration in the influent was below 200 mg L-1, the decolorization efficiency was up to 70% under the optimal conditions. As the dye concentration was higher than 100 mg L-1, the decolorization efficiency and COD removal in the BER were significantly higher than the sum of the same values in a single biological reactor and a single electrochemical reactor, which indicated that there was a synergistic effect between the electrode reaction and biodegradation. Kinetic analysis of color removal of RBR X-3B indicated that the rapid adsorption by microorganisms was weak and the decolorization process with time followed firstorder kinetics. GC-MS analysis of the degradation products suggested that the main reaction mechanism of RBR X-3B degradation was the reduction of N=N bonds on the biofilm cathode.2) A sealed up-flow three-dimensional biofilm-electrode reactor with ACF/Ti as anode, ACF/Fe as cathode and granular activated carbon (GAC, filled at the top of cathode) as medium was constructed. Compared with the integrated BER, the 3D BER could bear high load of dye concentration. When RBR X-3B concentration in the influent was as high as 1000 mg L-1, the decolorization efficiency was over 90%, but COD removal efficiency was only about 60%. Operating voltage of 1.0 V-1.5 V and hydraulic retention time (HRT) of 24 h were the optimum conditions of 3D BER. When nitrate nitrogen concentration in the influent was below 1.5 mM, denitrification and decolorization could be simultaneously realized in the 3D BER. The analysis of UV-Vis, FT-IR, GC-MS and HPLC showed that the rupture of azo bonds in the RBR X-3B molecules occurred mainly in the cathodic zone and the main reaction productions were aromatic compounds such as aniline, however, the degradation of these intermediates were carried out in the anodic zone.3) To improve the performance of the CW-MFC, three commonly used bio-cathode materials including stainless steel mesh (SSM), carbon cloth (CC) and granular activated carbon (GAC) were compared and evaluated, the operation parameters of the CW-MFC were also optimized. The results showed that GAC-SSM bio-cathode achieved the highest maximum current density of 63.06±1.92 mA m-2, and its maximum power density was about 55.18 mW m-2. GAC-SSM bio-cathode was most suitable for CW-MFCs application because of its large surface area and helpful capillary water absorption. With the increase of COD concentration in the influent, electricity energy generated by the CW-MFC first increased and then decreased. When influent COD concentration was 250 mg L-1, CW-MFCs obtained the highest power output, and the mean power density of the planted CW-MFC was about 43.76 mW m-2, which was 41.92% higher than that of non-planted CW-MFC. Periodic voltage fluctuations of planted CW-MFCs were caused by the effects of light/dark cycles on physiological activities of plants, and the influent COD concentration significantly affected the amplitude of oscillation. With the increasing of HRT, the power output of CW-MFC increased to the maximum and then decreased, and the optimal HRT was 72 h. The power density of the CW-MFC increased with the increase of phosphate buffer solution (PBS) concentration in the influent, however, when the PBS concentration was over 10 mM, the growth of Ipomoea aquatica was restrained, so the optimal PBS concentration was 5 mM.4) The removal effects of RBR X-3B by combined process of 3D BER and CW-MFC (only water connected) were studied. When influent dye concentration was below 1000 mg L-1, the decolorization efficiency exceeded 96%, and COD removal efficiency was 78.86%-90.78%. The highest power outputs of CW-MFCs were obtained when the influent dye concentration was 600 mg L-1, and the maximum power densities of the two CW-MFCs were 29.54 mW m-2 and 32.46 mW m-2, respectively.5) Two CW-MFCs were connected in series form, and the performeance of cell stack was studied. The results showed that the output voltage of cell stack was less than the sum of the value of individual CW-MFCs when operating alone. The output voltage of cell stack decreased greatly with the decrease of external resistance. When the external resistance was 100 Ω, the CW-MFC with larger internal resistance appeared voltage reversal. Two CW-MFCs stack (connected in series) and 3D BER were integrated in aspects of material and electricity energy. When RBR X-3B concentration in the influent was maintained at 600 mg L-1, the mean output voltage of CW-MFCs stack was about 0.253 V, and the decolorization efficiency and COD removal efficiency were 91.15% and 78.59%, respectively. The removal effect of dye wastewater by the coupled system was superior to that by 3D BER and CW-MFC alone. |
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