Reduction And Mechanism Research Of Azo Dye In Plug Flow Baffled Bioelectrochemical System

Azo dyes are the kind of aromatic compounds which contain one or more azo bonds in molecular structure,largest applied in current industry,they are frequently used for textile dying,paper making and printing industries due to firmne ss,acid and alkali resistance and antibiosis.However,azo dyes are difficultly biodegrade d and possess high chroma,their metabolites are highly toxic and cancerigenic,azo dye waste water cause serious threat to ecosystem and human health.There are numerous printing and dying industries in China,the color removal and detoxification from printing and dying wastewater are always one of the major concern in China as dye-containing wastewater has grown increasingly.Traditional physical and chemical treatments cost highly and generate toxic and harmful intermediates.Anaerobic biological treatment is able to decolorize azo dyes efficiently,but the low microbial metabolism makes low efficiency of decolorization,besides lose of direct electron donor in wastewater make it hard to biodegrade azo dyes.Nowadays,Bioelectrochemical Systems(BES)have been one of promising wastewater treatment technology and develop rapidly in which microbes served as catalyst to make through redox on electrode,it combines the opportunities of biological and electrochemical methods.This study focus on BES biocathode to alizarin yellow R(AYR)decolorization and configuration of electrochemical microbial communities,AYR was selected as a model azo dye as it was widely used in industry.A plug-flow baffled bioelectrocatalyzed reactor(PFB-BER)was developed,after optimizing parameters it combined high efficiency of decolorization and low power cost;then a long-term plug-flow baffled bioelectrocatalyzed reactor-aerobic bio-contact oxidation reactor(PFB-BER-ABOR)was developed to analyze long-term mineralizing effect referring to the configuration of cathode biofilm microbial communities.A PFB-BER was developed based on the reactor configuration optimization,it realized that AYR decolorized rapidly under continues flow,1.27 times higher than open circuit(hydraulic retention time 4 h),the formation rate of p-phenylenediamine(PPD)and 5-aminosalicylic acid(5-ASA)was higher than 95% and 50% respectively,it occupied the reductive degradation sufficiently for AYR as applied 0.5V voltage and made cathode potential at around-0.9 V.With the hydraulic retention time(HRT)reduced,the decolorization rate dropped.When the HRT reduced from 8 h to 4 h,the decolorization rate reduced from 69.9% to 44.9%.Through increasing the electrode group can obviously improve the decolorization efficiency,the decolorization rate of 4h raised from 44.8% to 83.1%.When take energy consumption into consideration,we found that the double-electrode reactor with 4h HRT consumed lower energy than sole-electrode reactor with 12 h HRT under the same decolorization rate.It indicated that increased the electrode group properly could raise the decolorization rate and lower the energy consumption.In the BES biocathode,AYR can be decolorized rapidly(acetate: 0.1818±0.0139 /h;glucose:0.4620±0.0567 /h),1.5 times(acetate)and 3.9 times(glucose)to abiotic cathode(0.0.1197±0.0004 /h)respectively.AYR decolorization rate dropped as initial concentration increased and it increased as applied voltage increased;when the substrate changed to glucose,the AYR decolorization rate and metabolites generated rate was 3 times higher.After the model fitting,it was found that when AYR initial concentration was 130-135 mg/L and 155 mg/L and the applied voltage was 0.66 V and 0.58 V(acetate and glucose as substrate respectively),the AYR decolorization rate was the highest and the unit energy consumption was the lowest.After microbial community analysis,we found that acclimatized microbial structure changed enormously,Citrobacter,Enterococcus and Alkaliflexus were dominant genera when served glucose,Acintobacter and Achromobacter were dominant genera when served acetate.Different substrate made different microbial communities and resulted in different decolorization rate,it illustrated that when glucose served as electron donor AYR decolorization microbes were dominant so that improved the reactor performance.The long-term PFB-BER could decolorize AYR continuously and steady.The reductive metabolites(5-ASA and PPD)were further oxidative and mineralized in the aerobic bio-contact oxidation reactor(ABOR).After long-term operation,microbial community analysis showed that the electrode type and position apparently influenced the abundance and diversity.Ornatilinea was dominant in cathode biofilm,Acinetobacter,Pseudomonas and Geobacter was dominant in anode biofilm.The structure of biofilm was influenced by the contaminants greatly.It was proved that BES was an efficient method to reductive decolorize azo dyes,the PFB-BER was a new treatment model,and provided a new method to magnify the dye wastewater treatment.