Chemical Absorption-bioelectrochemical Reduction Integrated System For NO_x Removal From Flu Gas-preparation Of Bioelectrode And System Performance Test

With the perfect ending of energy saving and emission reduction process in the thermal power generation industry,small and medium-sized coal-fired industrial boilers have become another emphasis of nitrogen oxides treatment according to the 13th Five-Year Plan.Eventually it is essential to develop a highly efficient and clean technology for controlling NOx removal from flu gas.The chemical absorption-bioelectrochemical reduction integrated system(CABER)is based on the previous CABR system and uses biofilm electrode reactor to enhance the system operation through strengthening the reduction process.And electrode biofilm reactor is the core part of CABER technology This study used electrode modifications and established a new electrode bio film reactor,and was applied to the CABER integrated system with operation performance and electronic transfer mechanism explored later.The enhanced mechanism of electrochemical reduction is explored at the level of electronic utilization and microorganism.The aim of this study is to provide theoretical support and optimization direction for the efficient operation of CABERBased on the shortages of poor bioadhesion and low electron transfer rate of traditional graphite electrode,a polypyrrole(Ppy)film-modified electrode was prepared on a graphite substrate using potentiostatic method(0.9 V)doping with 0.075 mM NaPTS.Results of scanning electron microscopy(SEM)and electrochemical testing shows that the Ppy modified electrode had a larger specific surface area and excellent electrochemical performance.A new CABER denitration system was then established using the new Ppy electrode and is proved to have a better bioreduction performance and flue gas treatment load.Based on the good biocompatibility of Ppy modified electrodes,another polypyrrole-carbon nanotube(Ppy-CNTs)modified electrode was prepared using the previous Ppy electrode.The Ppy-CNTs-CABER system was also established using this new Ppy-CNTs modified electrode,whose bioreduction performance and flue gas treatment load were superior than previous Ppy-CABER and unmodified C-CABER system:The NO removal efficiency was up to 96%in the presence of 9%O2.From the aspect of electron transfer,the mechanism of enhanced bioreduction process in BER using new Ppy electrodes and Ppy-CNTs electrodes were investigated in small microbial electrolysis cell.The reduction performance and faraday efficiency of Fe(?)EDTA in three bioelectrochemical systems based on traditional graphite C electrode,Ppy modified electrode and Ppy-CNTs modified electrode increased in turn,which proved that Ppy modified electrode made the system have a higher electron transfer efficiency,thus promoting the electronic utilization efficiency of microorganisms,and ultimately strengthening the bioreduction process.The reduction mechanism of Ppy-CNTs electrode biofilm reactor,and electron transfer mode in Ppy-CNTs bioelectrode were verified in a process of ' e-?polymer film?biofilm?electron acceptor Fe(?)EDTA ':firstly,carbon nanotube modification formed a conductive network between the polymer films;secondly,'electrode?microorganism',and 'microorganism?microorganism ',two kinds of nanowires between the bio films were formed.From the aspect of microbial level,the changes of biofacies in the new CABER systems were then explored,and the internal reasons for the enhancement of bioreduction process were clarified.In the two bioelectrochemical systems based on Ppy modified electrodes and Ppy-CNTs modified electrodes,the biomass increased by 21.6%and 36.4%respectively compared with the traditional system.All three systems mainly consisted of denitrifying strains and iron-reducing strains,indicating a relatively stable microbial community can be obtained through self-regulation in the flue gas denitration system.Klebsiella,Petrimonas,Escherichia/Shigella,Phascolarctobacterium and Azospira were the dominant bacteria in three denitrification systems,which proved these strains have certain environmental tolerance.Alpha,Beta diversity and species abundance analysis shows that the microbial diversity enhances the environmental resistance and stability of the system.The introduction of nanowires in the Ppy-CNTs system also made the ratio of the two functional bacteria more reasonable,which resulted the best operation performance and reduction efficiency in the new CABER system using the Ppy-CNTs electrode.