Validation On Nitrogen Removal Performance Of Sulfate-Reducing Ammonia Oxidation

Anaerobic ammonium oxidation（Anammox）technology has become one of the research hotspots in the field of environmental engineering because of its economic and efficient nitrogen removal performance.Existing studies have shown that Anammox bacteria can utilize a variety of substrates as electron donors for metabolism.This discovery expands the application of anammox in wastewater treatment.For example,sulfate as electron acceptor anaerobic ammonium oxidation reaction（SRAO）provides a new idea for simultaneous desulfurization and denitrification of wastewater.However,there are still insufficient and divergent views on the denitrification performance and mechanism of sulfate anaerobic ammonium oxidation.In view of this,this paper used an Upflow Anaerobic Sludge Bed（UASB）to treat simulated wastewater,started a SRAO reactor,and investigated the denitrification performance of the system.Combined with the conversion of system substances and the analysis of the structural characteristics of the microbial community with 16S r RNA high-throughput sequencing technology,explored the denitrification mechanism of the SRAO process.The main research conclusions obtained are as follows:（1）The start-up and denitrification performance test study of the SRAO reactor found that ammonia nitrogen was removed to a certain extent during the entire operation of the reactor.When the concentration of influent NH₄⁺-N was 50 mg/L,Almost all were removed;when the concentration of influent NH₄⁺-N was 200 mg/L,the removal rate of nitrogen removal efficiency droped to about 40%.During the operation,the sulfate concentration in the inlet and outlet water remained basically the same,and the content of S^2-and S⁰ in the system were never detected.This indicated that sulfate was not participate in the anaerobic biological denitrification process as an electron acceptor.（2）Through screening of electron acceptors in the process of anaerobic biological denitrification,it was found that low-concentration DO,Fe³⁺,Mn⁴⁺,reactive oxygen species and other substances in influent water cannot become electron acceptors for anaerobic ammonia nitrogen conversion.The HCO₃^-added by the inorganic carbon source was the electron acceptor for the conversion of ammonia nitrogen in the process.（3）The HCO₃^-/NH₄⁺type anaerobic bioreactor operation test study found that when the NH₄⁺-N and HCO₃^-influent concentrations were 50 mg/L and 540 mg/L,ammonia nitrogen was basically removed;when the NH₄⁺-N concentration increased to 100 mg/L,the nitrogen removal rate was about 75%;gradually increase the influent HCO₃^-concentration,and the effluent NH₄⁺-N will first decrease and then increase.When the HCO₃^-concentration was 1080 mg/L,the nitrogen removal efficiency was the best（85%）,but when rised to 1350 mg/L,the nitrogen removal efficiency will decrease.It can be seen that providing a certain concentration of HCO₃^-can make the oxidation of ammonia proceed,and within a certain concentration range,the higher the concentration of HCO₃^-,the more thorough the ammonia oxidation will be.The analysis of the change of IC concentration in the inlet and outlet water shown that HCO₃^-may be used as an electron acceptor to participate in the system,which was called the bicarbonate--reducing ammonia oxidation reaction.（4）Comparing the microbial diversity and community structure of the two reactors,the results shown that the two systems have similar microbial community structures.At the phylum level,Chloroflexi dominates the system.While protecting the sludge structure,the increase in its abundance also shown that it was closely related to the nitrogen removal efficiency.At the genus level,the relative abundance of NOB in the system was small,while AOB was not detected.The relative abundance of Candidatus＿Kuenenia in An AOB decreased sharply with the progress of the reaction,and eventually decreased to less than 1%.Therefore,the traditional anaerobic ammonia oxidation reaction and the nitrification and denitrification reaction in the system did not play a dominant role in nitrogen removal process.Norank＿f＿＿norank＿o＿＿SBR1031 gradually became the dominant strain in the two systems with the reaction operation,the relative abundance accounted for the largest proportion,and the relative abundance change had a good corresponding relationship with the nitrogen removal efficiency in the system.Norank＿f＿＿Anaerolineaceae taked the second place.Limnobacter can alleviate the effect of external environment on nitrogen removal bacteria in the system,and also participated in the denitrification process of the system.（5）Use the PICRUSt2 method to predict the metabolic functions of microorganisms in the two systems.The results of metabolic pathways indicate that the system has rich metabolic diversity,which provided the possibility for different electron acceptors to oxidize ammonium.In addition,the study of homologous gene changes related to nitrogen conversion showed that glutamine synthetase was an important enzyme in the system that mediates the nitrogen cycle,followed by glutamate dehydrogenase（type II）.This paper has 31 figures,13 tables,and 139 references.