Study On The Effects Of Sediment Aeration On Nitrogen And Phosphorus Migration And Transformation In Urban Rivers Under Different Hydrodynamic Conditions

The eutrophication is a global water environment problem.The sediment is the main source of pollution in urban rivers,so its process of releasing and absorbing nitrogen and phosphorus is the key to influence the eutrophication of water bodies.This research relies on the national science and technology major project“Research and Demonstration of Integrated Control Technology for Linkage Water Purification of the Haihe River Branch and Tributaries Network”.Based on the full consideration of the hydrodynamic characteristics of the river network of the Haihe River and the existing research results of sediment aeration,the indoor circulating water tank simulation was carried out to study the migration and transformation of nitrogen and phosphorus by sediment aeration under different water flow conditions.The research can provide a technical support for the removal of nitrogen and phosphorus pollutants in urban eutrophication rivers.The main research conclusions are as follows:Water flow or sediment aeration can significantly promote the removal of nitrogen from the overlying water and sediment.When the water body flew at 2cm/s⁵cm/s,compared with the blank group,the NH₄⁺-N and TN removal rate of the overlying water increased by 59%⁶0%and 41%⁴5%,respectively;Sediment extractable state NH₄⁺-N and TN removal rate increased by 6%³2%and 11%¹9%,respectively.After the sediment aeration intensity set to be 2L/min with a stop-and-exposure ratio of 4:1to 0:5,compared with the blank group,the NH₄⁺-N and TN removal rates of the overlying water increased by 59%⁶5%and 30%³8%,respectively;the extractable state of the sediment NH₄⁺-N and the TN removal rate increased by 12%²7%and30%³8%,respectively.Compared with water flow or sediment aeration alone,the combination of water flow and sediment aeration can remove nitrogen from the sediment more effectively,thereby enhancing the overall nitrogen removal rate of the mud-water system in the end.Among the 10 senarios of combination measure,when the water flow rate was 2cm/s,aeration intensity was set to be 2L/min and the stop-and-exposure ratio was 0:5,the extractable state of the sediment NH₄⁺-N and TN removal rate were the highest,increased by 61%and 56%compared with the blank group.For the removal of phosphorus,the water flow or the aeration of the sediment can both significantly promote the migration of phosphorus from the overlying water to the sediment,thereby realizing the removal of the overlying water phosphorus.The removal rates of SRP and TP in the blank group were-67%and-72%,respectively.When the water flow was 2cm/s⁵cm/s with no aeration in sediments,the removal rates of SRP and TP in the overlying water reached 59%⁶0%and 41%⁴5%,respectively.When the sediment aeration intensity was 2L/min with a stop-and-exposure ratio of 0:5to 4:1,the removal rates of the overlying water SRP and TP reached 70%⁹0%and59%⁹0%,respectively.Compared with the measures of water flow or sediment aeration alone,the combination of water flow at 2cm/s⁵cm/s,sediments aeration intensity at 2L/min and stop-and-exposure ratio at 2:3⁴:1 can promote the phosphorus in the overlying water migrate to the sediment more effectively.Among the 10 scenarios of combined measures,when the water flow rate was 2cm/s,the sediments aeration intensity was2L/min and the stop-and-exposure ratio was 3:2,the SRP and TP removal rates of the overlying water were the highest,reaching 90% and 89% respectively.