Study On The Characteristic Of Sulfide Occurrence And Devulcanization Process In The Sediment And Overlying Water Of Urban Channels

At Sunan river network area, channels are densely distributed. The water flow is slow. The rivers are polluted and sediments deposition are serious. Sulphate flows into rivers by runoff and atmogenic deposit, and is stored in the sediment finally. Sediment-overlying water interface keeps the state of anoxic and reductive. The oxidation-reduction potential is low. Sulphate is deoxidized to sulfide with organic matter by SRB (sulfate reducting bacteria), which causes the accumulation of sulfide in sediment-overlying water system.This paper studies the sediment-overlying water system of city rivers. Though the methods of spot field investigation, quantitative monitor, model fitting and laboratory culture, the characteristic of sulfide occurrence and devulcanization process in the sediment and overlying water of urban channels are studied. The following researches are carried out in this paper.(1)There is much difference in the contents of sulfide and sulfate in sediment-overlying water system. The sulfide contents in overlying water is 0-0.136mg/L, sulfate is 37.1-542.0mg/L. The sulfide contents in sediment is 850.5-7538.3mg/kg , sulfate is 17.5-149.0mg/L.There is SRB in the overlying water and sediments. The range of the content are 70-3×10⁵ per ml, 1.5×10³-2.5×10⁶ per gram. This shows that SRB is existed widely, and that SRB in overlying is lower than sediment.(2) The depth distribution characteristics and influencing factors of sulfide, sulfate and SRB shows: sulfide increases early and then decreases during the top 40cm layer of the sediment. SRB and sulfate are higher in the surface layer than the subsurface and bottom layers of the sediment. Sulfide is influenced not only by pH or Eh, but also organic matter (OM) and SRB. There is an negative correlation between the sulfide and the organic matter, but positive correlation between the sulfide and SRB. (3) Based on the actual data of sediment in the city rivers, non-linear fitting of the depth distribution in the sediment of river is done. The result shows that this model is adequate for the depth distribution of sulfide in sediments of urban channels where is out of jamming. The applied range has its limitations.The fitted equation in Qiqiaoweng and Jinchuan river are better, which areC = 336641.5e^0.003h -48310.8e^0.018h-288371.1 and C = 35436.9e^0.026h -99.2e^0.016h -36888.7. The related coefficient is 0.981 and 0.978.(4) There is difference in exchange fluxes between the laboratory culture method and the concentration gradient method. Sulfide is oxidizable material and impressionable by the external environmental condition. Because the coefficient of diffusion is obtained by actual layered measurement, the results are impressionable by the external environmental condition seriously. The more the hierarchy number is, the more the influence is. The undisturbed samples are used by the laboratory culture method which is impervious by the external environmental condition, so the results are accurate.The laboratory culture method shows that the devulcanization rate of sediment-overlying water interface in Qiqiaoweng and Jinchuan river which are the typical rivers are 0.357 and 0.649 mg/l·h. The exchange fluxes of sulphate are 82.8 and 188.0 mg·cm^-2·a^-1 The exchange fluxes of sulfide are -0.177 and -0.586mg·cm^-2·a^-1 . Sulphate is diffused from overlying water to sediments, but sulfide is diffused from sediments to overlying water.