Sulfide Generation Characteristics Of Gravity Flow Sewage Pipeline Network And Microbial Analysis In Sediment

As urban infrastructure,sewer network plays an important role in the recycling of urban water environment.However,the problem of corrosion and odor caused by hydrogen sulfide is causing a huge threat to the pipeline network and society.The generation of hydrogen sulfide in sewer networks is a result of complex biochemical reactions.The fundamental way to control the sulfide production is to study the characteristics and rules of sulfide production in sewer networks and to understand the microbial structure in sewers.To have a better cognition on hydrogen sulfide emission characteristics in real sewer systems,field investigation was carried out in a city of Jiangsu Province.OdaLogRTx wireless gas detector was used to continuously monitor the inspection wells of residential quarters,agricultural markets and main pipes along the way.It was found that the hydrogen sulfide concentration in septic tank and grille well was very low and nearly zero,and the concentration in drop structure was high.When there were septic tank and grille well upstream,the hydrogen sulfide content in drop structure was the highest,which indicated that the sediment of grille well and septic tank played an important role in hydrogen sulfide production,and the structure of water falling well played a role in releasing sulfide.To further analysis the process of sulfide production in pipelines,the laboratory built sediment reactors to mimic the real sediment sewers.Sediment and sewage are collected from real sewage pipelines.The flow velocity and disturbance in pipelines are simulated by different shear forces produced by two kinds of stirring speeds.For 180 days,besides the determination of sulfide in effluent,periodic experiments will be carried out regularly,and biochemical reactions will be monitored vertically in situ by using thin film diffusion gradient technique(DGT)and HR-Peeper technique in deposition and liquid phases.It was found that the sulfide production rate under small shear stress was lower than that under large shear stress at the initial stage of the experiment.After 140 days,the sulfide production rate under two shear stresses was almost the same.The sulfide of the sediment under small shear stress mainly accumulated in the surface layer of 0-2.5mm,while that under large shear stress was mainly distributed in 0-10 mm.The microorganisms in sediments were further investigated by Illumina high-throughput sequencing.The results showed that the microorganisms in the initial sediment distribute evenly in different depths,while the methanogenic bacteria and sulfate reducing bacteria(SRB)in the stable sediment grow in different degrees.The abundance of methanogens was much higher than that of SRB bacteria,and the increase of Desulfobacca,Desulfomonile and Desulforhabdus in SRB bacteria was similar,suggesting that the increase of these bacteria might not be affected by shear stress.Desulfobacter,Desulfobulbus and Desulfomicrobium have more flora under large shear stress.Desulfobulbus and Desulfomicrobium are the dominant genus of SRB bacteria,accounting for 23% and 23.5% of SRB bacteria respectively.They mainly grow at 0-10 mm of the surface layer of sediment.