Enhanced Decolorization Of Azo Dye AB10B In Bioelectrochemical System And Mechanism Analysis

Azo dyes with highly high chroma and toxicity, is one of the difficulties in the field of wastewater treatment. The current treatment technology based on anaerobic process, but there are some disadvantages including low reaction rate and toxity shock. Bioelectrochemical systems (BESs) as a new wastewater treatment technology have been highly concern in recent years. Because microbes as catalyst, BESs have low cost, long life, no secondary pollution, is excellent prospects in wastewater treatment field, comparing traditional electrochemical methods. It has been demonstrated that azo dye can be decolorized and amines formation in cathode of BESs. Comparing the anaerobic technology, BESs can accelerate the decolorization rate and improve the efficiency in theory. However, BESs were limited in laboratorial scale, because of the cost including ion-exchange membrane (IEM) and cathodic noble metal catalyst.In this study, the IEM was canceled from BESs that the two-chamber configuration became to single-chamber configuration. It was appeared that anode biofilm was shocked by azo dye AB10B with toxicity. The shocked results were including the anode electrochemical activity is lost, resulting in20.5%of decolorization efficiency. To overcome the problem, a gradient increase of azo dye concentration was used to acclimate the anode biofilm to pollutant toxicity. Anode biofilm acclimation enhanced anti-toxic and electrochemical activity of anodic communities; in contrast, the un-acclimated anode biofilm was failed for azo dye removal when exposed directly in single-chamber BES. The dominant bacteria in anode biofilm community consisted of Geobacter (28.9%) and Thermovirga (15.9%), Thauera (4.4%)，respectively. By comparing the IEM before and after removal on decolorization, the BESs decolorization efficiency and rate were increased by9.3%of24h and3.7mg/hL from1.6mg/hL. Non-IEM BES has anaerobic decolorization by anode biofilm comparing BES with IEM. The decolorizational products of AB10B was consistent with the theory azo bond was reduced to amine groups. The main products were aniline and phenylenediamine which easily mineralized in aerobic process.It was studied that biocathode with low-cost and long-life, formed in non-IEM BES using anode biofilm as inoculation. During BESs operation，the microbes was found attaching on the surface of cathode and biomass increased obviously. Meanwhile, the currents of BESs was increased significantly with increase of cycles, average current was increased from the initial0.23mA to0.45mA and the decolorization efficiency was improved form the initial81.7%to93.6%. The polarized current was improved with the operation time and EIS also showed the Rct was decreased by93.6%. The decolorization process between biocathode and abiocathode obeyed the first-order dynamics. The reaction rate of biocathode was higher than abio-cathode. From the analysis on specific energy consumption, biocathode needs additional electric consumption duos to electrons were used to activities of life. With the applied voltage increased, the decolorization efficiency was improved continually, but excessive additional voltage could lead to enhanced hydrogen evolution, resulting in decreasing of current efficiency and energy consumption on decolorization of AB10B. Based on high-throughput sequencing, the community diversity of biocathode biofilm revealed that there very high difference from bioanode and the proportion of same OTUs was only25.1%in all OTUs. The reason of this difference was suggested that different electrode condition influence the communities of biofilm above. There were a lot of bacteria including extracellular electron transfer and decolorization in cathode biofilm that may be key function in biocathode to decolorizition of azo dye. The dominant bacteria in biocathode community consisted of Thermovirga（14.5%）and Thauera （8.2%）and Comamonas (3.3%).To further study the biocathode for azo dye decolorization, especially the biocathode mechanism, the pure bacteria WYZ-2was isolated from biocathode of BESs and it belongs to Pseudomonas by identification. When the electrode as the sole electrons donor, WYZ-2could live on the surface of electrode that make the polarized current increased to0.35mA from0.13mA and the Rct of working electrode was decreased to255Ω from720Ω after WYZ-2inoculation. An unknown redox enzyme possibly involved in electron transfer between electrode and microbes. From polarized current and polarized potential by CV, the electrochemical activity of working electrode with WYZ-2was improved when AB10B as electron acceptor，comparing with blank working electrode. WYZ-2strain enhancing decolorization that needs a low electrode potential，but it is difficult to accelerate the decolorization when the bio-electrode was polarized at higher potential obviously.