Study On N₂O Emission In Aged Refuse Bioreactor Landfill

Ex-situ nitrification and in-situ denitrification nitrogen removal bioreactorlandfill, which solves the problem of ammonia accumulation in traditional anaerobicbioreactor landfill with simple single recirculation has been proposed as a promisingstrategy for sustainable landfill management.However nitrous oxide (N2O) will beinevitable produced during the nitrification and denitrfication process in thesystem.The early study showed that the aged refuse bioreactor which the nitrificationis the predominant process was the main source of N2O emission in ex-situnitrification and in-situ denitrification nitrogen removal bioreactor landfill.This paper focused on N2O production chareacteristic with the change ofoperational modes and the leachate quality by building simulated aged refusebioreactors, at the same time we study the microbial diversity by the PCR-RFLPtechnology. The results are helpful for the control of N2O in the ex-situ nitrificationand in-situ denitrification nitrogen removal bioreactor landfill.The results are asfollows:1. The amount of N2O were different as the reaeration modes were different, theN2O emissions were positively correlated with the concentration of nitrate and nitriteduring the whole period. In a typical cycle, the N2O conversion ratio were17.26%and13.63%respectively in the intermitted aerated semi-aerobic and the real semi-aerobicaged refuse bioreactor.2. Hydraulic loading and recirculation cycle were the main factors on N2Oemission.Too high or too low hydraulic loading is helpful to reduce the N2Oemissions,the N2O production goes up first and comes down,at8h reaches highestlevel,98.32±12.42ppm，is5and10times than that of5h and24h. So choosereasonable hydraulic loading and recirculation cycle is an effective way to reduceN2O emissions.3. The concentration of NH4+-N and COD were the key factors on N2Oemission.The N2O production increased with the increase of the concentration of NH4+-N.The concentration of N2O was3187±1018.72ppm when the concentration ofNH4+-N was2500mg/L，which accounted for5.3‰of the total nitrogen removal.TheN2O production was decreased with the increase of concentration of COD. Thehighest concentration of N2O was26312.3±2993.7ppm,occurred when theconcenteation of COD was2000mg/L， which accounted for12.68%. Thereforecontrol the C/N ratio at a reasonable level can reduce N2O emissions.4. The change of salty on N2O emission can not be ignored. The N2O productionincreased with the increase of the concentration of salty.The concentration of N2Owas1270.00±336.25ppm when the salty was30g/L，which was about6~117timesthan that of lower salty.5. Nitrosomonas, Thauera, Alcaligenes, Bacillus, Pseudomonas, Thiobacillusdenitrificans were the main microorganisms involved in the nitrogen removal in thetwo reaeration mode bioreactors. Aerobic denitrification process may be the main wayfor the N2O emissions.