Application Effect And Risk Evaluation Of Chemical Agents In The Treatment Of Black And Odorous Water

The treatment of black and odorous water in cities is the focus of urban construction.In the long-term water quality maintenance stage after the completion of the main black odorous water body in the city,external pollution such as overflow pollution in the combined system,rainwater in the initial stage of the split system,and wet and dry sedimentation will eventually collect in the sediment of the water body,forming a secondary black odorous sediment,by continuously releasing pollutants into the water and cause water quality bounce and repeat black smell.Due to the high engineering,social and ecological costs of sediment dredging,before sediment accumulation conditions trigger dredging conditions,the scientific use of chemicals has a positive effect on consolidating the treatment effect of black and odorous water body and maintaining long-term water quality.However,due to the lack of technical guidance documents and standardized market management,In the application process of this technology,there are chaos such as incorrect selection of chemicals,unreasonable dosage of chemicals,and unscientific methods of chemicals dosage,which have led to a surge in environmental risks,technical risks and market risks.Aiming at the practical problem that the confusing naming and classification of chemicals in the market makes it difficult to choose the correct chemicals,this study conducts a classification study of chemicals through the collection and arrangement of literature and cases,and classifies them into oxidants flocculants,stabilizers and algicides based on the position and effect of the action,to facilitate the rational selection of chemicals.Carry out comparison and selection experiments of common chemicals,and use beaker experiments and pilot experiments to study,under the influence of potassium ferrate（K₂Fe O₄）,poly aluminum chloride（PAC）,and potassium persulfate compound salts（K₂SO₄·KHSO₄·2KHSO₅）,sediment and overlying water’s redox potential（ORP）,ammonia nitrogen（NH₃-N）,total nitrogen（TN）,orthophosphate（PO₄-P）,total phosphorus（TP）,turbidity（NTU）,chemical oxygen demand（COD）and other indicators to form comparison recommendations.Carry out experiments on the effects of different dosages on the application effect and the ecological safety of the water environment,and initially determine the concentration range of typical chemicals through beaker experiments The main conclusions were that the sodium hypochlorite（Na Cl O）concentration range was between 371.2μL and 346.06μL,and the K₂Fe O₄ concentration range was among 0mg/L～50mg/L,and further research in the pilot test and establish different dosages and water body ORP.The relationship and the effects of different dosages of chemicals were investigated,and the effects of different dosages on the promotion and stabilization of ORP in water bodies were emphasized.The results showed that the overlying water within 60 days of Na Cl O and K₂Fe O₄ maintained high ORP values.However,the increase of the ORP value of the composite salt of PAC and K₂SO₄·KHSO₄·2KHSO₅ within 60 days is not ideal.The correlation between the ORP of the water body and the DO and T in the pilot reactor with different concentrations of chemicals was statistically analyzed.The correlations of water quality indicators of different concentrations of chemicals are different.Finally,the reasonable dosage of chemicals was determined.The acute toxicity experimental study of oxidant K₂Fe O₄ on the fourth instar larvae was conducted.Through the 48h acute toxicity experimental study on the fourth instar larvae combined with K₂Fe O₄.The relationship between the changes in the ORP of the initial and delayed doses of K₂Fe O₄ in the aqueous solution and the 48h acute toxicity average mortality of the fourth instar larvae.Mortality fluctuates with fluctuations in the ORP value.In summary,the research results of each part can provide a basis for selecting chemicals for the application of chemicals in the restoration of secondary sediments and long-term water quality maintenance of urban black and odorous water body,and providing methods demonstrations for determining the dosage of chemicals and the water ecological environmental risk assessment.