Study On Pollution Characteristics And Disposal Methods Of Sediment In Urban River Course

With the development of society,the pollution problem of urban rivers has become increasingly serious,and black odor has appeared in some rivers,which has seriously affected the life of surrounding residents.Under the premise of effective control of exogenous pollution,dredging of river sediment can effectively reduce endogenous pollution,which is an important measure to improve water quality and water ecological environment.In this paper,the X and Y of two typical tributaries of the river flood in Dongguan City are taken as the research objects.Through on-site investigation,sediment detection,data analysis,sediment dredging and treatment,the branch gushing is treated.Finally,the purpose of controlling the endogenous pollution of sediment and improving water quality is achieved.The main contents and conclusions are as follows:(1)By detecting and analyzing the distribution characteristics of TN,TP,organic matter and heavy metals in the surface and vertical subsurface sediments of X and Y,it is found that the content distribution of TN,TP,organic matter and heavy metals in the surface sediments of X and Y is significantly different along the flow direction,which has spatial heterogeneity and is greatly affected by exogenous pollution.The correlation and pollution sources of the sediment detection indexes of the X and Y of two tributaries of the river flood were analyzed respectively.The results showed that the organic matter in the sediment detection indexes of Branch Chong X was significantly correlated with TN,TP,Cd and Pb,indicating that the change of organic matter and TN,TP,Cd and Pb were synchronous,and the contents of TP,TN,Cd and Pb partly came from organic compounds.TN was significantly correlated with TP and Pb,indicating that the nitrogen and phosphorus elements were all discharged from the same pollution source.There is a significant correlation between Cd and Pb,and Cd and Pb have homology.There is a significant correlation between organic matter and TN and Cr,while there is little correlation between organic matter and TP,indicating that TP may come from inorganic phosphorus,TN from organic nitrogen,and heavy metal Cr exists in organic combined state,while other heavy metals exist in residual state.The significant correlation between As and Pb indicates that As and Pb are homologous.The vertical characteristics of TN,TP and heavy metals in sediment are gradually accumulated from the upper to the lower layer,reaching the maximum at a certain depth,then gradually decreasing,and finally tending to be stable.The vertical distribution of different pollutants at the same point has the same change rule,showing good synchronization,but the content is greatly different.(2)The comprehensive pollution index method and organic pollution index method were used to evaluate the pollution degree of TN,TP and organic matter in the branch drainage sediment respectively.It was found that the pollution degree of TN and TP was mainly heavy pollution,and the floating mud layer >the transition layer>the undisturbed soil layer,indicates that the TN and TP in the bottom mud are mainly released from the nutrients in the water,thus it is speculated that there may be environmental problems such as eutrophication in the water body.The organic pollution of the bottom mud of branch chung is 75% of fertilizer pollution,and the pollution grade is Ⅲ,which is serious.The heavy metal pollution of river sediment was evaluated by single factor method,geoaccumulation index evaluation method,Nemerow comprehensive pollution index method and potential ecological risk index method.The results of the single factor method were similar to those of the geoaccumulation index evaluation method.It was concluded that the most polluted area of the X of tributaries of the river flood was mainly X4 and X6 sample points.The comprehensive pollution index method concluded that the most polluted area was X4 sample point,and the potential ecological risk index method concluded that the most polluted area was X4 sample point.However,in general,X4 sample site has the most serious pollution and the highest ecological risk.The pollution degree of the Y of tributaries of the river flood is lower than that of the X of tributaries of the river flood.Cd,Cr and As are the main factors affecting the pollution degree of heavy metals in sediment.(3)On the premise of exogenous pollution under control,in order to control the endogenous pollution,the sediment in situ physical technology,chemical treatment and bioremediation in situ and sediment dredging technology is compared and adaptability research,it is concluded that for the research object of this paper adopts the method of sediment dredging can more thoroughly remove pollution;Visual stratification method,inflection point method,background value method and ground accumulation index method are adopted to comprehensively determine the dredging depth of sample points X1,X2,X3,X4,X5,X6,Y1,Y2,Y3,Y4,Y5 and Y6 is 30 cm,23cm,137 cm,103cm,30 cm,93cm,78 cm,127cm,128 cm,107cm,113 cm and 110 cm respectively.In order to prevent the secondary pollution of dredged sediment,the dredged sediment was disposed by mechanical dewatering and consolidation integrated treatment process and the stable solidification of heavy metals in the sediment,so that the sediment could be "reduced,stabilized,harmless and resourced".After treatment,the leaching concentration of heavy metal Hg,Cr,Cd,As and Pb decreased by 94%,64%,68%,54% and 52%,all of which did not exceed the standard value of agricultural soil utilization,and could be used for the resource utilization of soil for landscaping and ecological bank protection.