A Comparative Study On Sulfur-based Autotrophic Denitrification And Its Mechanisms

Sulfur-based autotrophic denitrification is an important technology for nitrogen removal from water.As it needs no organic carbon resource and causes no secondary contamination,it has unique engineering value on nitrogen contamination control.Based on the lab-scale experiment,the microbial community structure was analysed and the mathematic simulation was tried in this study,in order to explain the mechanisms of sulfur-based autotrophic denitrification,and to supply the primary support for the parameter optimization and running control.For this purpose,two identical lab-scale biofilter reactors were applied,with thiosulfate and elemental sulfur as the respective eletron donor.The two reactors were run under the completely same environmental conditions and running conditions and the denitrification performance was compared.Then the sludge samples were taken from both reactors and analysed with high-throughput sequencing in order to clarify the microbial community inside.Finally,a mathematic simulation was built to qutatively describe this bio-process of autotrophic denitrification.Comparison of the denitrification performance of the two reactors showed that the thiosulfate system was superior to the elemental sulfur systems on treatment capacity,and the denitrification stability.For a successfully started and stably running reactor,stopping the addition of inorganic salts has no evident influence on thiosulfate system in a short time of 2-3 months and the running cost could be saved.Additionally,the low temperature of 8-12℃ had obvious influence on both reactors.But the thiosulfate system could remain the nitrate removal of 70-80% if the HRT was long enough,while the elemental sulfur system showed a great removal variation of between 40-80%.To investigate the microbial community structures and biodiversity in sulphur-based autotrophic denitrification processes with different electron donors,two lab-scale autotrophic biological denitrification biofilter reactors were applied,using thiosulfate and elemental sulfur as the respective electron donor.The sludge samples were taken during the stable operation,then the microbial community composition and structures were analyzed with high-throughput sequencing technology.The results revealed there were 49 phyla,431 genera of different bacteria detected in sodium thiosulfate system,45 phyla and 413 genera in sulfur system.Both of them contained a large number of functional bacteria,Thiobacillus,Kosmotoga and Dechloromonas,each with the relative abundance of more than 5%.Thiovirga,another genus of autotrophic denitrifying bacteria,was quite abundant in the thiosulfate system but very low in the sulfur system,implying the different predominant genus.In both systems,the relative abundance of genus Dechloromonas increased with higher nitrate concentration,indicating its adaptability in relatively higher concentration.The phenomenon that Thiobacillus and Thiovirga predominated at the bottom and the upper part of the reactor verified that they might function in the steps of reducing nitrate to nitrite and transferring nitrite into nitrogen,respectively.Based on ASMN,a dynamic model was built to simulate the process of thiosulfate-driven denitrification process.The simulation results showed that the model could simulate and predict the process well,and that it may help the prediction,assessment and directing the design and running in the future.