Removal Of Nitrogen Oxides From Exhaust Gas Of Boilers Using Aerobic Denitrifying Bacteria Under Thermophilic Condition

Nitric oxide can lead to tropospheric ozone depletion and is the main constituentof photochemical smog. It may also form nitrous acid by reacting with moisture in theair, which has been implicated in acid rain. With the environmental awarenessincreasing, more rigorous environmental laws are introduced, and china had limitedNOxemission to100mg/m3in GB13223-2011. The policy makes the new removaltechnologies which are economical and environmental necessary. The bioprocessesare proved to be effective, reliable and cheap techniques for the treatment of gas withrelatively low concentration of pollutants. The combustion processes of fossil fuelsused in power plants, vehicles and other incineration processes contribute a lot to airpollution. As the flue gas vent out from the coal-fired power plants include3%~8%oxygen, and the temperature is40~50℃. So it’s necessary to culture and inoculatean aerobic denitrifying bacterial under thermophilic condition.In the study, an aerobic denitrifier was isolated from the active sludge underthermophilic condition. And its aerobic denitrification activity was evaluated whenthe temperature was45℃. This bacterium was Gram positive, short rod. And thedenitrification capacity of this bacterium was pretty high when the pH values changedfrom6.0to9.0and the DO values ranged1.0mg/L to5.0mg/L, the removalefficiency of NO3-was up to95%within24h. The growth curve of this denitrifyingbacterium was measured. The logarithmic growth phase continued for18h, and the stablebreading period lasted for approximately30h.The new device—the combination of the Bio-Filter (BF) and Bio-trickling Filter(BTF) was employed to test the removal of NOxusing aerobic denitrifying bacteriaunder thermophilic condition. Effects of the inlet concentration of NOx, empty bedresidence time (EBRT), the concentration of oxygen and liquid flow on the removalefficiency of NOxwere investigated in the new device. The removal efficiencyreached to93.5%at the inlet NOxconcentration of1100ppm, the inlet O2concentration of8%(V/V), the nutrient liquid flow rate of10L/h, and thecorresponding empty bed retention time (EBRT) of40.2s. However, the removalefficiency of NOxwas less than90%with the inlet NOxconcentration over1300ppmor EBRT down to40s. Using the Deep Bio-film theory and Monod kinetic equation, the dynamics modelfor microbial flue gas denitrogenation was obtained. The simulation results are ingood agreement with the experimental values when compared to the removalefficiency with different inlet concentration of NOxand empty bed residence time,and the model has been proven to be accurate and credible.