Study On Nitrate Wastewater Treatment By Coupling Thiosulfate-Driven Denitrification With Anaerobic Ammonia Oxidation

Anammox is an efficient and energy-saving wastewater denitrification process among many water denitrification processes.However,the problems of unstable nitrite supply and nitrate residues in Anammox process limit its wide application.Among many solutions,short-range autotrophic denitrification has been widely studied due to its high efficiency and environmental protection.Thiosulfate is a non-toxic and highly bioavailable inorganic reducing agent,which is very suitable as an electron donor for short-range autotrophic denitrification.Therefore,in this experiment,Anammox,SAD and TDDA reactors were established to enrich anammox sludge,sulfur autotrophic denitrification sludge and explore the coupling process of anammox and sulfur autotrophic denitrification.During the enrichment of sludge,the effects of pH on the denitrification performance of anaerobic ammonium oxidation,the effects of different S/N ratios on the denitrification performance of sulfur autotrophic denitrification process,the mechanism of nitrogen accumulation in sulfur autotrophic denitrification process and the distribution of microbial population structure were investigated.In the coupling process of anaerobic ammonium oxidation and sulfur autotrophic denitrification,the effects of different S/N on the nitrogen removal performance of the coupling system,the proportion of nitrogen removal pathways in the system,the nitrogen and sulfur metabolism pathways,and the relationship between nitrogen metabolism functional genes and related species were mainly explored.The following points were concluded from the above study:（1）Batch experiments showed that the optimum pH range of anammox process was7.5～8.0 at 30°C.In addition,Candidatus＿Brocadia and Candidatus＿Jettenia are the main bacteria in the anammox reactor.（2）In the sulfur autotrophic denitrification process,the nitrite accumulation effect was the best when S/N=1.0,and the nitrite accumulation efficiency was as high as 54.86%.When S/N=1.5,the denitrification effect was the best,and the total nitrogen removal efficiency reached 92.14%.Batch experiments showed that when thiosulfate was used as the electron donor,the nitrate removal rate was much higher than the nitrite removal rate,and the nitrite accumulation was very obvious.When elemental sulfur was used as the main electron donor in the system,the nitrate removal rate was less than the nitrite removal rate,and the nitrite accumulation rate decreased.In addition,the functional genus of the sulfur autotrophic denitrification system is mainly Thiobacillus,and its relative abundance increases with the increase of S/N ratio.（3）Due to the formation of a large number of S⁰-Anammox particle structures in the anaerobic ammonia oxidation and sulfur autotrophic denitrification coupling system at S/N=2,the denitrification effect at S/N=2 and 1 is basically the same.Batch experiments showed that the nitrogen removal pathway that was always in an absolute dominant position in the coupling system was S₂O₃^2--PDN-Anammox.When S/N=2,the contribution of S₂O₃^2--PDN-Anammox decreased,and the contribution of S⁰-PDN-Anammox increased significantly.（4）The relative abundance of complete denitrification functional genes（norBC,nosZ）and anaerobic ammonia oxidation functional genes（hzS,hdh）in the coupled system was high at S/N=1 and 2.When S/N=1,more nitrate dissimilatory reduction to ammonium（DNRA）functional genes（nrfA）appeared in the system,indicating that there was a DNRA pathway in the coupled system when S/N=1.Thiobacillus not only has denitrification functional genes narGHI,napA,nirKS,norBC and nosZ,but also has DNRA functional gene nrfA,which indicates that it can simultaneously perform denitrification and DNRA denitrification processes.（5）The thiosulfate oxidation pathway is mainly the S⁰ oxidation pathway,that is,thiosulfate is first converted into sulfate and elemental sulfur under the action of SoxAX,SoxYZ and SoxB.Elemental sulfur is reduced to sulfide under the action of DsrL,and sulfide is oxidized to sulfide under the action of Dsr AB,and then further converted into APS under the action of AprAB.Finally,it is completely oxidized to sulfate under the action of Sat.