The Characteristics and Mechanisms of Simultaneous Azo Dye Degradation and Bioelectricity Generation Using A Constructed Wetland-microbial Fuel Cell

Author:Fang Zhou

Supervisor:li xian ning


Degree Year:2017





Biorefractory organic waste water became sticking and hot point of waste water treatment process because of it is of poor biochemical purification ability,chemical property stable and high biological toxicity.In recent years,microbial fuel cells(MFCs)gained widely attention because it is a new technology of waste water treatment.MFCs gained widely attention because they can recover chemical energy from waste water directly and transform it into electric energy.This study utilized the structure similarity of constructed wetland(CW)and microbial fuel cell(MFC),embeded the cathode and the anode of MFC into CW,built the new constructed wetland-microbial fuel cell(CW-MFC)which can operating under continuous flow,and used it to purify the biorefractory organic waste water for the first time.Also,it has succeeded in the azo dye waste water decolorization and simultaneously bioelectricity generation.This study investigated the promotion of the bioelectricity generation on the decolorization and the promotion of the wetland plants on the bioelectricity generation.The performance of the azo dye decolorization and degradation in the cathode and anode and the interrelationship of the electricity generation and purification performance between the cathode and the anode was studied deeply.The mechanisms of azo dye decolorization and degradation was analyzed,too.The main research contents and results were listed as follow:1)The promotion of CW-MFC bioelectricity generation on the azo dye ABRX3 decolorization and COD removal were studied.The results show that,CW-MFC could prompted the ABRX3 decolorization efficiency effectively and COD removal efficiency by 17%and 23.0%,compared to the open circuit CW-MFC(as the traditional CW),respectively.The highest decolorization and COD removal efficiency was 95.24%and 90.40%,respectively.The electrons provided by co-substrate oxidization were leading-out to cells by electrogenic bacterias,the contact probability of ABRX3 and electrons was promoted.Furthermore,the current could promote the process of metabolism of microbe,and promote the decolorization provided by microbes.The abundance of electrogenic bacterias G.Sulfurreducens and Beta Proteobacteria was higher in the anode layer of the close circuit CW-MFC than the open circuit CW-MFC.2)The cathode plants could increase the dissolved oxygen of the cathode layer,enhanced the cathode potential,and then enhance the output voltage of CW-MFC.The highest output voltage of CW-MFCs with plants in the cathode layer was 600 mV when there were no ABRX3 in the wastewater,and was 560 mV when there were ABRX3 in the wastewater.Cathode plants can promote the microbial biomass of cathode layer,with benefted the degradation of the decolorization products,and the plants can reduce the cathode internal resistance,too.3)The anode layer contributed the most to ABRX3 decolorization,the decolorization efficiency of the anode layer was as much as 65.32%.The co-substrate is the essential electron donor of ABRX3 decolorization and bioelectricity generation,however,there was only a small part of electrons which were provided by the co-substrate were used in decolorization and bioelectricity generation.Therefore the anode could keep a favourable decolorization and bioelectricity generation performance under the high ABRX3 lode.ABRX3 can poison the electrogenic bacterias,made the anode polarization more seriously,and inhibit the bioelectricity generation.The bioelectricity generation performance of the anode layer was effected obviously.Compared with the anode,ABRX3 was more likely to get electron from the co-substrates,therefore,when the bioelectricity generation performance was decreased because of the lack of the co-substrates,the decolorization performance could still keep in a high level.However,the decolorization effectively and the output voltage of CW-MFC with no co-substrate were all very low,the better co-substrates for the CW-MFC was glucose,for it’s appropriate solubility and formula weight.Compared with some co-substrates with smaller molecules,glucose cannot be degrade rapidly in the bottom layer,this benifit the decolorization and the bioelectricity generation of the anode layer.4)The azo dye decolorization in the cathode layer was observed in the air cathode,the decolorization capability of the cathode layer on the ABRX3 and the interrelationship between the anode and the cathode were investigated.The results indicated the anoxic region in the bottom of the cathode layer provided suitable oxidation-reduction potential for the azo dye decolorization.The electrons from the anode layer could take part in the reduction reaction and made azo dye be decolorized.Increase the cathode area or decrease the resistance benifited ABRX3 decolorization and the increase of the cathode exchange current density.This disproves enhance cathode reaction benifited ABRX3 reduction,made it more likely to get electrons.Cathode ABRX3 decolorization volume increased with the increase of cathode exchange current density.The highest cathode decolorization volume was 55.07 mg/L.Meanwhile,increase the cathode area can notablely promote the cathode potential and CW-MFC output voltage.The interrelationship between the anode and the cathode was:Properly increasing of current intensity benifited both the reaction of the anode and the cathode,however a too high current intensity may promote the cathode reaction and inhibit the anode reaction,which related to the electron competition between the anode and the cathode.5)The azo dye decolorization in the bottom layer and the anode layer was caused by the reduction reaction,azo bonds was broken by receive the electron.The products of azo dye decolorization were aromatic amines,include alcohols,ketones,lipids and amines.These products could further degradated in the anode and the cathode layer,and translated into small molecules.In the anode layer,electrons provided by co-substrate imultaneous supplied the azo dye decolorization and the anode,the electrons received by the anode transmitted to cathode from the external circut,a part of them was completed the half cell reaction in the aerobic zone of the cathode layer.The other part of the electrons reached the anoxic zone of the cathode layer,and reduce the azo dye and the products in the cathode layer.6)The operational condition and the structure had effects on the simultaneous azo dye degradation and bioelectricity generation.The ABRX3 percentage in the waste water had great influence on the azo dye decolorization.The type of co-substrates and the buffer concentration had great influence on the bioelectricity generation.At the same time,the type of co-substrates had great influence on the degradation of decolorization products.Glucose was a kind of suitable co-substrate for CW-MFCs.The decolorization and the bioelectricity generation performance frist increased and then decreased with the increase of hydraulic detention time.The decolorization and the bioelectricity generation performance were best when the numerical of external resistance was similar to the internal resistance.Electrode gap influenced the bioelectricity generation performance by influenced the ohm resistance.Cathode project area influenced the cathode and the anode decolorization and the bioelectricity generation performance by influenced the cathode and the anode exchange current density.In this study,the decolorization and the bioelectricity generation performance were beat when the ratio of the cathode and the anode vertical projection area was 3:2.