Coupling Effects In The Fate Of Endogenous Sulfur, Iron And Nitrogen From Malodorous River Sediments UnderAerated Turbulence

Urban development needs good water environment as a basic guarantee. In order to mitigate serious pollution of urban water bodies, a lot of treatment projects for malodorous rivers have been carried out in many cities across China. Artificial aeration is an important remediation measure because of its unique advantages. Despite the implement of these remediation projects, the overload of nitrogen pollutants becomes an increasingly prominent problem. Nitrogen releasing from river sediments gradually becomes the main source of N-pollution after effective control of external N-pollution input.’Blackening’ substances （iron sulfide） and’cause smelly’ substances （volatile sulfides） have close relationship with endogenous nitrogen in some recent studies and in our group’s previous studies as well. These substances can directly or indirectly affect nitrogen cycling in malodorous rivers. This study, funded by the National Natural Science Foundation of China （No.41101471）, was based on our group’s previous studies of the fate of endogenous nutrients under different aeration disturbance modes. The interactions between endogenous nitrogen, sulfur and iron were preliminarily discussed, and the response mechanisms of bacteria from sediments to different aeration disturbance were revealed. This study was aimed at providing a new perspective on strengthening endogenous nitrogen removal in sediments, which is important to the treatment of malodorous urban rivers both in theory and in practice. The main results are as follow:（1） Aeration was in favor of the removal of NH₄⁺-N and TN in the overlying water. The concentration of NH₄⁺-N and TN in the overlying water was 6.00-6.74 mg-L"1 and 18.27～19.41 mg-L-1, respectively. With respect to all of the aeration systems, the removal efficiencies of NH₄⁺-N in the overlying water can be reached at higher than 90%, with the maximum removal efficiency being 94.0±5.0%; the maximum removal efficiency of TN was 73.0±4.8%. Meanwhile, aeration was in favor of the removal of NH₄⁺-N and TN in the sediment-water interface, with the maximum removal efficiencies of NH₄⁺-N and TN being 37.3%±7.7% and 29.1±2.5%, respectively.（2） NH₄⁺-N and TN were released from sediments to overlying water through sediment-water interface under aeration disturbance. Nitrification rate and denitrification rate of the sediment-water interface were both higher with aeration than without aeration. The maximum nitrification and denitrification rates were 37.3±1.6% and 28.4±3.2%, respectively.（3） Aeration was in favor of the transformation of reduced sulfur to SO42- in the sediment-water interface. The maximum removal efficiency of AVS in sediments was 66.7±2.2%, and the maximum removal efficiency of S2- in sediment-water interface was 34.7±3.3%. The dynamic correlation analysis of the principal forms of nitrogen and sulfur under different aeration conditions indicated that sulfur-driven nitrate reduction was limited. Reduced sulfur was firstly oxidized to thiosulfate or elemental sulfur, and then oxidized to SO42- under aeration.（4） Aeration was in favor of the transformation of Fe2+ to Fe3+ in the sediment-water interface. The removal efficiency of Fe2+ in the overlying water was 48.3%-60.6%, and the maximum removal efficiency of Fe2+ in sediment-water interface can be reached at higher than 50%. The dynamic correlation analysis of the principal forms of nitrogen and iron under different aeration conditions indicated that the oxidation process of Fe2+ to Fe3+ was not in coupling with the reduction process of NO3--N to NH₄⁺-N. However, the possibility that oxidation of Fe2+ coupled with the process of NO3--N reducing to NO2--N cannot be ruled out.（5） Results from high-throughput sequencing analysis show that the predominant phylums of bacteria were Proteobacteria, Chloroflexi and Firmicutes. Among Proteobacteria, most were δ-Proteobacteria. Meanwhile,6 genera nitrifying bacteria, 18 genera denitrifying bacteria,1 genus anaerobic ammonium oxidizing bacteria,4-5 genera sulfur oxidizing bacteria,3 genera sulfate reducing bacteria and 26 genera iron reducing bacteria were also confirmed, but no bacteria which had been identified to be involved in sulfur autotrophic denitrification and iron autotrophic denitrification was detected. Therefore, we suspect that both sulfur autotrophic denitrification and iron autotrophic denitrification did not exist in malodorous river water before and after aeration.（6） Bacterial community structures in the surface sediment were affected with various degrees under different aeration modes. The quantity of Proteobacteria, Firmicutes and Chloroflexi decreased, while the quantity of nitrifying bacteria, denitrifying bacteria and sulfur oxidizing bacteria increased. The growth of sulfate reducing bacteria was inhibited.（7） Through the PCA analysis between environmental factors and the dominant bacteria species, it was found that DO, NH₄⁺-N and Fe2+ from the overlying water and Fe2+ from the sediment were significant influence factors for dominant bacteria species in the surface sediment of malodorous urban river.