Study On Microbial Community Diversity And N₂O Production Pathway In Semi-aerobic Bioreactor Landfill

Semi-aerobic bioreactor landfill has the characteristics of accelerating garbage stabilization and effectively removing high concentration of ammonia nitrogen in leachate and has obvious advantages in the practical engineering application.The consumption of organic matter and the removal of ammonia nitrogen are mainly dependent on the metabolism of microorganisms.And the removal of ammonia nitrogen is mainly through the microbial nitrification and denitrification.However,during the nitrification and denitrification of microorganisms,N₂O greenhouse gases are produced,posing a serious threat to the environment.And the mechanism of nitrification and denitrification to produce N₂O is not very clear in the field of aerobic bioreactor landfill.Therefore,in this experiment,the N₂O production pathway and its contribution rate of semi-aerobic bioreactor landfill are studied by high-throughput sequencing and ¹⁵N stable isotope labeling.And the follows are the main results.（1）In the analysis of leachate water quality,semi-aerobic bioreactor landfill has the technical advantages of rapidly degrading organic matter and solving the problem of high concentration ammonia accumulation,and the leachate effluent index has reached the basic steady state at the 255th day.During the whole experiment,the water quality of leachate in different periods changes greatly.The high concentrations of COD_cr and ammonia nitrogen have similar laws in the leachate,and the reactor has good treatment effect on COD_cr and ammonia nitrogen.（2）In the study of microbial community diversity,the diversity of microbes in the early stage of garbage stabilization is higher than that in the later stage.The Simpson index for the previous sample is 0.1-0.2 and the late is 0.3-0.6,and the middle abundance is lower than that in both ends.During the experimental operation,the proportion of nitrifying microorganisms is very low,and the proportion of microbes with denitrification characteristics in the later period is larger than that in the early stage（3）In the process of N₂O production,the N₂O production is lower in most of the time,and the N₂O accumulation occurres in the latter part of the experiment.The initial stage of the experiment is the adaptation period,during which the microorganisms are in the adaptation stage and are affected by the initial conditions.And the N₂O production is larger.With the gradual adaptation of microorganisms,microbial flora is basically stable,nitrification and denitrification intensity are in a balanced state and N₂O production is relatively stable.In the later stage,the accumulation of N₂O production increases rapidly,and when the concentration of NH₄⁺-N decreased gradually,the nitrifying bacteria system and the denitrifying bacteria system reaches a new equilibrium,the NO_x-N accumulation disappears and the N₂O production decreases.（4）About the N₂O production pathway,N₂O mainly produces in the microbial denitrification process in the semi-aerobic bioreactor landfill and the proportion is 79to 92%.Nitrification reaction process accounts for the proportion of 8 to 21%,of which the main is self-nitrification.The contribution rate of nitrification and denitrification to N₂O production varies with different trash stabilization periods.The main reason for the increase of N₂O production may be the accumulation of NOx-N in leachate,and the microbial community structure changed with the degradation of waste.And the proportion of denitrifying microorganisms increases,leading to an increase in N₂O production.