The Research On Pollutant Degradation Rule In The Sewage Outlet Downstream Of The Three Gorges Reservoir Area

The water of2000m downstream of the sewage outfalls of JiGuanShi sewagetreatment plant was selected as the research object. Field in-situ test and laboratoryexperiments were adopted as methods to research pollutant degradation rules. Theresponse relations between pollutants degradation coefficient and the impact factorswas quantitative analysis by using structural equation model. The highest impactfactor was selected as the independent variables on the basis and the empiricalformula was fitted by impact factor to determine the degradation coefficient. Themain contents were as follows:(1)Field in-situ test mainly monitored the change trend of flow velocity,temperature, dissolved oxygen and pH value of four factors. The change range of flowvelocity was large and the flow velocity of shoreside monitoring section was muchsmaller than which of river center monitoring section. Water temperature was at20°Cand change range was little. The variation range of dissolved oxygen was7mg/L-13mg/L and the variation range of pH value was6-8. Water was in neutral aerobiccondition, which was beneficial to the degradation of pollutants.(2)According to the basic principle of pollutants degradation, one-leveldegradation model was selected to study the degradation of CODMn, TN, TP andammonia nitrogen. In field in-situ test, the pollutants degradation coefficient ofshoreside monitoring section was much smaller than which of river center monitoringsection. Laboratory experiments were set up eight velocity gradient to study velocity’sinfluence on the degradation coefficient. The pollutant degradation coefficient wasgradually increased along with the increase of flow velocity.(3)Structural equation model was applied to quantitatively research theresponse relationship between pollutant degradation coefficient and four impactfactors of flow velocity, temperature, dissolved oxygen and pH value. Within thescope of this study, four impact factors and pollutant degradation coefficients arepositive correlation and pollutants degradation coefficient values was increased alongwith the increase of the impact factors. Among these factors, the flow velocity had thelargest effect on the degradation coefficient and was the most important influencefactor. The influence of dissolved oxygen and pH on the degradation coefficient wasrelatively approximate. Temperature effect on the degradation coefficient was relatively small. The correlation coefficient of flow velocity of dissolved oxygen inexogenous variable was0.05. Velocity increased, dissolved oxygen value alsoincreased accordingly.(4) On the basis of the quantitative analysis results of structural equation model,the wild field measurement experiment data as the foundation, the velocity was tookas independent variables and pollutants degradation coefficient was took as thedependent variable, and the empirical formulas of the coefficient of flow velocity andpollutant degradation were fitted. Linear function, power function and exponentialfunction was select to fit the empirical formulas between CODMn, TN, TP, ammonianitrogen, the experience formula and the four indicators. After comparative analysisthe experience formula of the three kinds of model, the results showed that the powerfunction model was the highest and most suitable fitting model. In this studyconditions range, the empirical formulas could be applied to rapidly calculate thecoefficient of pollutant degradation.