| Nitrogen oxides (NOx) are major atmospheric pollutants, and its main source ofemission is from the flue gas of power plants. When NOxconcentration rises above acertain threshold, it will cause various environmental and health problems, such asacidification, photochemical smog, depletion of the ozone layer, formation of PM10and PM2.5, and reducing visibility. It is extremely urgent to remove NOxfrom flue gaswith a gradually serious problem of NOxpollution and an increasing attention ofpeople on environmental quality. Metal chelate absorption coupled with biologicalreduction is a promising strategy for NOxremoval with the characteristics of hightreatment efficiency, low running costs, and no secondary pollutant production.However, mixed strains of suspended bacteria are used in current researches, whichmay cause some problems, such as low density of advantageous bacteria makes thesystem unstable, poor tolerance to inhibitors, and Fe(II)EDTA-NO has a stronginhibition effect on Fe(II)EDTA reduction. Hence, the bioreduction rate ofFe(III)EDTA is the rate-controlling step of this system. In order to tackle thesedisadvantages and enhance the bioregeneration of Fe(II)EDTA, an integrated processof metal chelate absorption coupled with two-stage bio-reduction using magneticallystabilized fluidized bed as bioreactor was developed. In this dissertation, theperformance and the mass transfer-reaction kinetics model of Fe(III)EDTA andFe(II)EDTA-NO reduction using immobilized bacteria was investigated; theoperation regime of magnetically stabilized fluidized bed was determined; thefeasibility of this new integrated system for removal of NOxwas demonstrated; theeffects of various operating parameters on NO removal was investigated, and themathematical model for NO removal in this integrated system was developed.The experimental results revealed that a higher bioreduction rate and a bettertolerance to inhibitors were achieved with immobilized bacteria than with freebacteria. Fe(II)EDTA-NO had a strong inhibiting effect, but Fe(II)EDTA had no effect,on Fe(III)EDTA reduction using immobilized bacteria. Fe(II)EDTA acceleratedFe(II)EDTA-NO reduction, whereas Fe(III)EDTA had no effect on it. So, the use of the two stages of regeneration was necessary. In addition, the effect of internaldiffusion on Fe(III)EDTA and Fe(II)EDTA-NO reduction was negligible, and therate-limiting step was the bioreduction process. The reduction of Fe(III)EDTA andFe(II)EDTA-NO using immobilized bacteria could be described by a first-orderkinetic model.The regime between the minimum fluidization rate and the transition rate wasthe operational regime of magnetically stabilized fluidized bed. Increasing themagnetic field intensity was favorable for enlarging the operational region ofmagnetically stabilized fluidized bed. The magnetic field stimulated Fe(II)EDTA-NOreduction and had no obvious effect on Fe(III)EDTA reduction, whereas it decreasedNO removal efficiency at a higher magnetic field intensity. Increasing the inlet NOconcentration or gas flow rate would cause a decrease in NO removal efficiency andan increase in elimination capacity. The integrated system had a good tolerance to O2,and the concentration of O2, SO2and liquid circulation rate had no significantinfluence on NO removal. Increasing the amount of scrubber solution or Fe(II)EDTAconcentration was favorable for NO removal, whereas high concentration ofFe(II)EDTA had a negative effect on bioreduction process. The consumption ofglucose was0.1g/h. The stopping running of the integrated system had no obviouseffect on NO removal.The integrated metal chelate absorption and two-stage bio-reduction processusing magnetically stabilized fluidized bed reactors was proved to be feasible andeffective to remove NOx. The integrated system showed a good stability and a highNO removal efficiency and elimination capacity. During a21d continuous operation,the NO removal efficiency could keep on above90%with an elimination capacity of61.42g NO/(m3·h), and the magnetic Fe3O4-chitosan microspheres structure did nochange during the long-term operation. Based on the principle of gas-liquid masstransfer and the material balance equation, the mathematical model was established.The established model indicated that the removal efficiency was related to theproperties of the absorber (e.g., column diameter, packing height, the interfacial areaof mass transfer), gas loading, and the bioregeneration of Fe(II)EDTA. |
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