Characteristics And Mechanism Of N₂O Emission From Sulfur Autotrophic Denitrification

Nitrous oxide(N2O)is an important greenhouse gas,and the biological denitrification process is considered as an important artificial source of N2O emissions.The study on the characteristics and mechanism of N2O release in the denitrification system of autotrophic organisms is of great significance for controlling and reducing the release of greenhouse gases.In this study,sulfur-based autotrophic denitrification membrane bioreactor was established to achieve high-efficiency denitrification and nitrogen removal.Simultaneously,the N2O emission process and rules of sulfur-based autotrophic denitrification under different conditions were explored,and sulfur-based autotrophic and traditional heterotrophic denitrification was compared through parallel experiments.Combining the characteristics of N2O emissions from denitrification and heterotrophic denitrification processes with the variation of main functional genes to analyze the advantages and mechanisms of sulfur-based autotrophic denitrification to reduce N20 emissions.The main research conclusions are as follows:(1)From the perspective of denitrification efficiency and N2O emission,autotrophic denitrification had the best effect when Na2S2O3 was the electron donor,S/N was 10,pH was 7.0 and the concentration of NO3--N was low.N20 emission of autotrophic denitrification was lower than the traditional heterotrophic denitrification,indicating that autotrophic denitrification was the more environmentally friendly biological denitrification technology for water treatment.The absolute and relative abundance of the nosZ gene in the autotrophic system was much higher than that in the heterotrophic system,indicating the macroscopic response of microbial communities to N2O emission in the denitrification system.(2)A sulfur-oxidizing autotrophic denitrification system in the membrane biofluidized bed reactor was established.When the reactor was treated with NO3--N concentration 300 mg/L and HRT was 2 h,NO3--N and NO2--N accumulation were eliminated in the effluent.The highest proportion of N2O emission TN was 0.06%,which was far lower than heterotrophic denitrification of 0.25%in the literature.The reactor denitrification performance and N2O emission control were the best when the reactor influent pH was 7.5.(3)The N2O emission decreased as the copies of the functional genes nosZ increased.The high influent concentration of NO3--N would inhibit the growth of 16S rRNA and functional genes;The copies of functional gene nosZ was highest at pH 7.5,and N2O emission was inhibited,which validated the low N2O emission of the reactor under this condition,providing a theoretical basis for the advantage of N20 emission reduction sulfur-oxidizing autrotriphic denitrification.