Process Intensification And Regulation Mechanism Of NO_x Removal From Flue Gas In A Chemical Absorption-biofilm Electrode Reactor Integrated System

Chemical absorption-biological reduction (CABR) integrated approach is a promising technology for NOx removal from flue gas proposed in recent years, which combines the advantages of chemical absorption and biological reduction. In order to break through the limitation of bio-reduction rate, chemical aborption-biofilm electrode reactor (CABER) integrated system was established. Based on the existing research and the analysis of technical bottlenecks, the bio-electrochemical reduction mechanism of Fe(III)EDTA in the biofilm electrode reactor was investigated; the cooperative and competitive interaction between glucose and cathode electrons was studied; the bio-electrochemical reduction mechanism of Fe(Ⅱ)EDTA-NO was studied based on the bio-electrochemical reduction mechanism of Fe(III)EDTA; the shift of bacterial community, biomasses and surface structures of the biofilm with different current densities were all investigated.The main original conclusions of this dissertation are as following.(1) The enhancement of Fe(III)EDTA reduction rate is mainly attributed to the bio-electrochemical reduction in the biofilm electrode reactor. Most of the cathode electrons are transformed to hydrogen according to Faraday’s law under sole electrochemical action. When there exists microorganisms, the reduction rate of Fe(III)EDTA can be significantly improved by using hydrogen as electron donor to reduce Fe(III)EDTA. Four transformation pathways of cathode electrons in the biofilm electrode reactor were obtained based on electron conservation: directly reduction, indirectly reduction, storage and release. Among them, directly reduction and indirectly reduction are responsible for the enhancement on Fe(III)EDTA reduction. Furthermore, part of the hydrogen can be transformed to organics, such as methanol, when there lacks external carbon source in the reactor. The synthesized organics can not only used as carbon source but also used as electron donor when electron donor is insufficient.(2) It is found that cathode electrons are the more efficient electron donor for reduction of Fe(III)EDTA according to the comparison of reduction rates with cathode electrons and glucose as sole electron donor. This is mainly thanks to the in-situ utilization of hydrogen on the surface of cathode packings, which has better mass transfer driving force than glucose. However, cathode electrons cannot be fully used to reduce Fe(III)EDTA because part of hydrogen will be used to synthesize organics. The reduction potential of cathode electrons can be released when appropriate amount of glucose was added. At this condition, glucose is used as carbon source and cathode electrons are used as electron donor. When glucose concentration exceeded this level, excessive glucose could also be used as electron donor. Based on the cooperative and competitive interaction between glucose and cathode electrons, the reduction rates of Fe(III)EDTA with different combinations of glucose and impressed current were investigated. 0.06 A of impressed current and 200 mg L-1 glucose was suggested to be the best combination of electron donors via factorial analysis.(3) Cathode electrons can directly reduce Fe(II)EDTA-NO, which accounts 20% of reduction contribution, and indirectly reduce Fe(II)EDTA-NO via reduction of Fe(III)EDTA. N2 was confirmed as the end-product of Fe(II)EDTA-NO reduction with N2O as an intermediate. Additionally, the end-product would change to NO2- and NO3- when Fe(II)EDTA was insufficient, and keep a certain amount of Fe(II)EDTA in the liquid phase can reduce second pollution. It is found that bio-electrochemical action can reduce the accumulation of N2O. Nearly 87% Fe(II)EDTA-NO were reduced using cathode electrons as electron donor via direct and indirect ways. Since the contribution of electrochemical action is limited, Fe(II)EDTA is considered the prior electron donor. Furthermore, the maximum reduction rate of Fe(II)EDTA-NO in the biofilm electrode reactor was obtained by kinetic analysis. Compared to that in the biotrickling reactor,13.04 mol m-3 h-1 is nearly 50% higher.(4) Current density has significant impacts on the bacterial community, biomass and surface structure of biofilm. Despite the biomass was lowest with 100 A m-3 NCC of current density, which is 0.06 A of impressed current, the microbial diversity was best and few crack and cavity was found on the surface of biofilm, which indicating that the biofilm was in ideal state. Through the analysis of bacterial community shift without impressed current, the biomass of dinitrifiers were dominant while the biomass of iron-reducing bacteria accounted for only 3.58%. The ratio of iron-reducing bacteria increased gradually with current density. The increase of iron-reducing bacteria biomass will lead to the enhancement of Fe(III)EDTA reduction, which consequently enhanced the reduction of Fe(II)EDTA-NO. Therefore, the increase of iron-reducing bacteria biomass is one of the internal causes of enhanced reduction by bio-electrochemical action. In conclusion,0.06 A is the optimal impressed current for this biofilm electrode reactor.