| Biological nitrogen removal process could release large amounts of greenhouse gases(GHGs)in wastewater treatment,especially the CH4 and N2O,and this process has become one of the most important anthropogenic GHGs emission sources.Traditional nitrogen removal process not only caused secondary pollution with GHGs emission,but also has the defects of high running cost and so on.In recent years had found nitrite-dependent anaerobic methane oxidation(n-damo)process,which is using CH4 as carbon source to proceeding microbial nitrogen removal and without N2O emission.This process has realized the organic combination between carbon cycle and nitrogen cycle and has provided an important way in reducing the emissions of GHGs.N-damo process is performed by "Candidatus Methylomirabilis oxyfera"(M.oxyfera)bacteria,which is affiliated with the uncultured NC10 phylum.However,because of the long doubling time and strict growing conditions,as well as many other questions,the n-damo process could not be widely used in wastewater treatment.Therefore,basing on the perspectives of searching for optimal inocula and optimizing the environment of enrichment,this study was conducted to research about distribution characteristic and directional function control of n-damo bacteria.The research content mainly had three aspects:(1)mastered the distribution of n-damo bacteria in northern China,and determined controllable factors of affecting the n-damo bacteria distribution;(2)investigated the effect of carbon source on the nitrogen transformation process by n-damo bacteria,and comprehensive assessed the effect of GHGs emission reduction;(3)using modem molecular biology methods,explored the microbial mechanism of nitrogen removal process under different carbon sources conditions.The main conclusions are as follows:(1).N-damo bacteria was widespread in the northern China,with different distribution,which was mainly influenced by biomass retention time and environmental factors,a longer biomass retention time,as well as low ammonia nitrogen and high nitrite nitrogen concentration were better for the growth of n-damo bacteria.Farmlands were selected as the optimal inocula because of much more abundance,activity and diversity of n-damo bacteria.(2).Carbon sources had significant influence on the nitrogen removal.Nitrogen removal was detected in all three reactors with adding acetate,methanol and CO2/H2 as carbon source.Reactors with organic carbon source had the highest nitrite removal efficiencies,which were about 1.3 times of the reactor with inorganic carbon source,but the reactor with inorganic carbon source had the highest nitrogen removal rate,which was about 1.4 times of reactors with organic carbon source.Reactor with inorganic carbon source had the highest nitrogen removal rate and the lowest nitrite removal efficiency,this mainly due to the lower MLVSS concentration and the higher n-damo activity.(3).Under the different carbon sources conditions,the nitrogen removal mechanisms of n-damo enrichment culture were different.NC10 bacteria(>50%)under different carbon source conditions was enriched successfully,and become the dominant bacterial group,reactor with inorganic carbon source had the highest abundance of NC10 bacteria,which was about 4.73 times of reactors with organic carbon source,but in situ production and consumption of CH4 led to unique n-damo bacteria community;adding acetate and methanol reactors had the highest abundance of nosZ gene,and found that 13.1%and 12.2%of the nitrite nitrogen were removed through heterotrophic denitrifying process;based on the quantitative of mcrA gene,proved that n-damo process was completed by methanogens and NC10 bacteria together when added other carbon sources except for the CH4.(4).Introducing the n-damo process in the nitrogen removal process could dramatically reduce GHGs,particularly N2O emission.The conversion ratios of N2O-N in all reactors were in the range of 0.03%-0.11%,compared with other wastewater treatment processes,n-damo process had reduced more than five times,this was attribute to the n-damo process,which could reduction of nitric oxide(NO)directly for nitrogen(N2)and without intermediate N2O;at the same time,comprehensive considering the release of CH4 and N2O,found that the total Global Warming Potential(GWP)from the reactor with inorganic carbon source was only a quarter of the reactors with organic carbon source. |
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