Microbial Electricity Generation Enhances Decolorization And Detoxification Of Azo Dye Wastewater In Anaerobic Baffled Reactor

Azo dye is a compound containing-N=N-bond in molecular structure, which is one of the most widely used dyes in the world. Because of the stable molecular structure and the more toxic aromatic amine products of azo dyes, the treatment of wastewater containing azo dyes has caused considerable concern. Anaerobic baffled reactor (ABR), which introduced the separation and flow technology to improve the hydraulic condition of the traditional anaerobic reactor, start-up speed, microbial retention and differentiation ability, was widely used in azo dye wastewater treatment. However, the COD and chromaticity of the effluents are still high and the biological toxicity increased due to the decolorization products of aromatic amines after ABR treatment. A large number of studies show that microbial electricity production can enhance the degradation and transformation of pollutants. What’s more, the anaerobic activated sludge contains lots of electron acceptors for electrode anaerobic respiratory and electricity generation as well as coupling with organic pollutants degradation microorganisms. It is speculated that when adding electrode into ABR compartment as microbial anaerobic respiration electron acceptor for microbial electricity generation, the functions and activities of the microorganisms in the system would be significantly improved and the decolorization, degradation and detoxification of azo dyes would be promoted.To test this hypothesis, we designed ABR-MFC coupled reactor with a total volume of 3.6 L and 3 chambers. Then a series of electrode with carbon brush anode and carbon felt cathode was placed in the chambers. Reactors were operated at room temperature, the operation cycle is 96 d, the concentration of AO7 in a concentration gradient 200 mg/L,400 mg/L,800 mg/L by step, HRT=2 d. The decolorization and degradation of Acid Orange 7 as well as the ecological toxicity of the products in ABR and ABR-MFC were monitored. Combined with the characteristics of microbial community structure and functional activity, the main results of the study on the degradation of azo dyes were studied:Electricity produced by microorganism significantly improved anaerobic baffled reactor decolorization and degradation of AO7 and detoxification. When the influent concentration of 400 mg/L, wastewater color and the soluble COD removal rate in the ABR-MFC reached 96.3% ± 1.7% and 72.8% ±2.5%, with removal rate 90.7% ± 1.4% and 66.9% ± 2.4% in ABR, respectively. According to the eco-toxicity based on Daphnia magna survival, ABR-MFC can significantly reduce the toxicity of dye wastewater. At the same time, under a certain AO7 influent concentration, the unit biomass in the reactor was slightly lower than that of the control group, but the dehydrogenase activity of the reactor was slightly higher.Microbial electricity production changed the community structure of indigenous microorganisms in the ABR significantly, and the microbial community structure in the three compartments under the condition of the power generation became uniform. Among of them, ABR-MFC compartments abundance of larger microorganisms were Pseudomonas sp., Sporolactobacillus sp. and Clostridium sensustricto sp.; the dominant bacteria in the ABR first compartment was Methanosaeta sp., and the third compartment was Arcobacter sp..In summary, this study constructed ABR-MFC coupled reactor with innovatively adding electrode to the anaerobic baffled reactor for azo dye wastewater treatment. With a variety of analysis and detection technology including environmental engineering, environmental microbiology, electrochemical and ecological toxicology, we found that structure and functional activity occurred significant changes under the condition of ABR with the electricity production. Under these conditions, the decolorization, degradation and detoxification of AO7 were obviously enhanced, and the recovery of electricity was realized. These results provide a rare reference for the realization of enhanced treatment and energy utilization of toxic organic wastewater.