Study On The Mechanism Of Two-stage Coupled Process Of Anammox And Sulfur-based Autotrophic Denitrification

Anaerobic ammonium oxidation(anammox)has the ability to simultaneously remove nitrite and ammonium,and the new biological nitrogen removal process can reduce energy consumption and has attracted much attention.However,11%(accounting for total nitrogen)of nitrate in anammox metabolites,which makes anammox unable to remove nitrogen efficiently,thus causes its limitations in engineering application.Considering the economic benefits and nitrogen removal performance,sulfur-based autotrophic denitrification(SAD)was chosen to remove the nitrate produced by anammox in this study.The two-stage coupled process of anammox and SAD was constructed to explore the feasibility of the coupled system,the stability under the substrate fluctuation and the efficiency of nitrogen removal.(1)The construction feasibility of coupled process was analyzed through the startup and operation.The results showed that the coupled process successfully started up in 12 days and kept stable operation.The nitrogen removal efficiency of the anammox and the coupled process were 86.70 ± 1.03% and 99.15 ± 0.68%,respectively,which showed that the coupled process could solve the problem of ineffective nitrogen removal by anammox.Anammox effluent had a promotion for SAD.The positive synergy between the anammox and SAD verified the feasibility of the two-stage coupled process structure of anammox and SAD.(2)The stability of coupled process was analyzed through the substrate fluctuation conditions.The results showed that the nitrogen removal efficiency of the coupled process was 95.27 ± 1.51% and 93.44 ± 0.96% respectively under the excessive nitrite and excessive ammonium.The total nitrogen removal efficiency was as high as 99.08 ± 0.68% with nitrification-side branch connected between anammox and SAD.After 21 days starvation,the coupled process still had a good recovery ability,and the operation performance was fully recovered in 16 days.Anammox granular sludge and SAD biofilm responded to the fluctuating substrate by EPS for the stability of the coupled process.The bacterial community showed good tolerance and recovery in different conditions.The stable bacterial ecology determined the high stability of the coupled process.(3)The nitrogen removal efficiency of the coupled process was analyzed by comparing the coupled SAD and the alone SAD.The results showed that the preferential removal of nitrite was appeared in the SAD,in which the removal efficiency of nitrite and nitrate were 100% and 69.9%,respectively.The obvious changes of pH,ORP,EPS and AHLs in anammox effluent potentially caused that activity of Nir increased and activity of Nar decreased.The relative abundances of Longilinea,Thiobacillus and Methyloversatilis should be related to the removal of nitrite.There was no accumulation of nitrite in the coupled process,which reflected the high efficiency of the coupled process.In conclusion,the two-stage coupled process of anammox and SAD was feasible,operated stably under the fluctuating substrate,and maintained efficient nitrogen removal.The results of this study provided an effective solution to the limitation of nitrogen removal and technical support of engineering application for anammox process.