Effect Of Dissolved Organic Matter On Endogenous Sulfur In The Interventional Denitrification In Urban River

Difficult to remove nitrogen is an urgent problem in current urban river management process.Sulfur is an important element for malodorous river.And its effect on nitrate reduction is worthy of attention.In addition,as an important part of sediment,dissolved organic matter?DOM?can provide energy for bacteria,but also serve as carrier for nitrogen transformation on mud-overlying interface.How DOM affects the process of endogenous sulfur involved in denitrification of urban river is an academic question worthy of discussion.Based on the analysis of the characteristics of sediments DOM in typical urban rivers,this paper used incubation experiments to discuss effect of DOM on the denitrification and different sulfur forms on denitrification under the action of DOM.Subsequently,the interaction of nitrogen and sulfur under different control methods was studied by means of simulated urban river.High-throughput sequencing was used to analyze the microbial mechanism of nitrogen and sulfur,in order to provide technology for strengthening the removal of nitrate in urban river.The main findings of this paper are as follows:?1?Based on the study of dissolved organic matter?DOM?concentration and characteristics in typical urban river sediments,it was found that significant differences of DOM content and characteristics among urban rivers.The sediment DOM content of Gongye river was higher?1868.51±45.31mg/kg?,while that of Taopu and Zhangjing river was close?500.51±49.20 mg/kg,631.20±40.62 mg/kg,respectively?.DOM in Gongye river was mainly composed of fulvic acid of small molecule,and protein-like substance was relatively high.However,humic acid of large molecule was low.DOM in Taopu river was mainly composed of humic acid of large molecule.DOM in Zhangjing river was between the two,and contains more alcohol,phenol,ether and other substances.?2?Based on the study of sediment dissolved organic matter on the denitrification,it was found that between low concentration?24-72 mg/L?,DOM showed positive correlation with denitrification.The removal rate of TN was increased by 47.09±0.52%compared with blank.When the concentration of DOM exceeded 72 mg/L,denitrification did not increase significantly.In addition,the system had obvious nitrite accumulation under the action of DOM.After adding the acetate,the phenomenon of nitrite accumulation disappeared,and the nitrate removal rate increased by 11.90±0.05%compared with the non-cooperation group.High-throughput sequencing results revealed that Proteobacteria,Bacteroidetes,and Chloroflexi were the main dominant bacteria.When DOM concentration increased,the abundance of Pseudomonas increased significantly than blank?0.51%?,accounting for 2.01%-13.15%.The abundance of Pseudomonas and Thauera in S6?72mg/L DOM and sediment as substrate?with the best denitrification was 13.15%and 15.86%,respectively.It is speculated that DOM is used to enhance the denitrification of sediment.In addition,the abundance of Phenylobacterium in S8 without acetate increased to 1.89%,which participated in incomplete denitrification,may be one of the reasons for the nitrite accumulation in this group.?3?The effect of sulfur forms on the denitrification under DOM is different.For reduced sulfur?sulfide,sulfur,pyrite,thiosulfate?,the addition of DOM promoted their denitrification.However,the optimal dosages of sulfur forms were different,3mM,3mM,4mM,3mM,respectively.And the removal rate of TN was improved by 13.09±0.11%,9.72±0.06%,8.21±0.18%,10.09±0.05%than blank.It was speculated that DOM promoted autotrophic denitrification of reduced sulfur.For the oxidized sulfur?sulfate?,DOM has no obvious effect on the removal of TN.The denitrification of sediment was affected by different sulfur forms when acetate was added with DOM.DOM enhanced the removal of nitrate by sulfide under the cooperation of acetate,and the removal rate increased by 5.22±0.05%compared with the group without coordination,which also promoted the transformation of nitrate to ammonia and nitrite in the system.However,the effect of sulfate on denitrification was not significant.High-throughput sequencing showed that Brevundimonas,Pseudomonas and Thiobacillus were the main dominant bacteria.The relative abundance of Sporosarcina in sulfide group was higher than blank?13.37%?.The relative abundance of?-Proteobacteria was the highest in the sulfur group?17.40%?,and the dominant autotrophic denitrifying bacteria in this group was Thiobacillus?2.62%?.In addition,the relative abundances of Pseudomonas?2.56%,3.04%?and Acinetobacter of sulfide and sulfur group were significantly increased.It was speculated that there was mixture of autotrophic and heterotrophic in these systems,which improved denitrification.In addition of Thiobacillus,the main denitrifying bacteria in thiosulfate group is Desulfobacca that typical desulfurizing bacteria,accounting for 1.26%.?4?Through the study of river simulation system,it was found that the TN removal efficiency was different under the action of DOM with sulfur forms in urban river.DOM enhanced the removal of TN by sulfide and sulfur,with removal rates of 21.52±0.35%and 17.91±0.26%higher than blank,respectively.It was speculated that the formation of autotrophic denitrification was promoted by sulfur and sulfide as electron donors,sulfate was not helpful for the TN removal by DOM.The abundance of Chloroflexi increased from 8.19%to 12.28%-21.50%.There were also differences in nirK-type denitrifying bacteria among the sulfide and sulfur groups.The main denitrifying bacteria in the sulfide group were unclassified_fhalobiaceae?5.14%?and unclassified_pproteobacteria?11.93%?.In addition,the Sulfurovum?0.47%?which could use S^2-as electron donor also appeared.The main denitrifying bacteria in the sulfur group was unclassified_pproteobacteria?6.91%?,and Desulfomorile which related to sulfur removal,also appeared.Its relative abundance increased by 0.32%compared with the original sediment.