Effects Of Loading Rates And N/S Ratios In The Sulfide-dependent Autotrophic Denitrification (SDAD) And Anammox Coupling System

Based on the Sulfide-Dependent Autotrophic Denitrification（SDAD）process and the Anammox process,the SDAD-Anammox process can achieve simultaneous removals of ammonia,nitrate,and sulfide.There have been several studies focused on the coupling process of SDAD-Anammox.However,information about the performance of this coupling system at different substrate loading rates and N/S ratios,and the detailed interactions（competition and cooperation）between Anammox and SDAD bacteria still remain unclear.Therefore,this paper carried out related studies on Anammox,SDAD,and SDAD-Anammox process:Firstly,the Anammox reactor was quickly started,and TN removal efficiency reached89.6%.The Haldane model was used to fit the effects of NO₂^--N concentrations on the Anammox.Results indicated the half-saturation concentration Ks was 2.971 mg/L,the inhibition coefficient Ki was 456.353 mg/L,and the maximum reaction rate Vmax was 1.524kg/m³·d.High-throughput sequencing results showed that Candidatus Kuenenia and Candidatus Brocadia increased to 20.0%and 2.7%,respectively,indicating the successful enrichment of Anammox bacteria.Secondly,adding enough glucose into the SDAD system can achieve the synergistic nitrogen removal of the SDAD and the heterotrophic denitrification（HD）.And NO₃^--N removal efficiency reached over 91.0%in the SDAD-HD system.Sulfide removal efficiency reached100%,which demonstrated that the addition of glucose did not affect its removal efficiency.The Alpha diversity analysis demonstrated that when the system changed from the SDAD to the SDAD-HD and then to the HD,the relative abundance of microbial species gradually declined.However,the microbial diversity was the highest in the SDAD system,followed by the HD system,and the least in the SDAD-HD system.High-throughput sequencing results showed that the relative abundance of Thiobacillus and Sulfurimonas increased slightly after adding 80 mg/L glucose,indicating that SDAD bacteria and HD bacteria could be in cooperative status.Finally,the SDAD-Anammox coupling system was well started up.When the NLR was1.52 kg N m^-3 d^-1,TN removal efficiency was 86.7%.When the NLR further increased to 3.36kg N m^-3 d^-1,the system was over-loaded,resulting TN removal efficiency dropped to 77.0%.In the meantime,N/S reduced from 2.0 to 1.5,NO₃^--N removal efficiency reached over 89.4%.Sulfide removal efficiency was 100%during the entire experiment.Batch experiment results showed that the rates of PSDAD and Anammox were always higher than SSDAD,ensuring the dominance of Anammox.High-throughput sequencing results indicated that Candidatus Kuenenia,Thiobacillus,and Sulfurimonas were the main functional microorganisms in the SDAD-Anammox coupling system.When SLR increased,the relative abundances of Thiobacillus and Sulfurimonas increased significantly.Although the relative abundance of Candidatus Kuenenia was much lower than that of Thiobacillus and Sulfurimonas,it still remained active,indicating that the main functional microorganisms involved in the coupling system were in harmony status.