Phosphorus Absorption Characteristics And Release Risk Assessment Of Sediments In The Receiving River Section Of Wastewater Treatment Plant

With the increasing number and scale of urban wastewater treatment plants,thewastewater treatment plant effluent is also increasing.Due to the limitations of wastewater denitrification and phosphorus removal technology,the wastewater treatment plant effluent still contains high nitrogen and phosphorus loads,which affects the water quality of the receiving water body and the health of the water ecosystem.This article takes 2.5km long upstream and downstream sections near the tailwater discharge of Caitianpu Wasterwater Treatment Plant on the Banqiao River in Hefei as an object.It is collected at a frequency of sampling every two months from October2018 to August 2019.The surface sediments and overlying water samples were analyzed for phosphorus morphology,phosphorus adsorption and desorption equilibrium concentration（EPC₀）,and biological concentration of the sediments at the control point（CP）above the discharge port and the three sampling points below（SP1,SP2,and SP3 in this order）Comparative analysis of abiotic phosphorus absorption potential,analysis of the impact of wastewater treatment plant tailwater discharge on phosphorus retention in the receiving river section,and assessment of the difference in impact of external carbon addition on phosphorus balance concentration and release risk.The main research results are as follows:（1）The average values of total phosphorus（TP）concentrations at the upstream and downstream of the discharge port are 0.161mg·L^-1 and 0.237mg·L^-1 and the SRP average values are 0.097mg·L^-1and 0.137mg·L^-1,respectively.And the order of TP and SRP concentrations at 4 points in the river is:wastewater treatment plant effluent>SP1>SP2>SP3>CP;the water quality of Banqiao River is basically weakly alkaline,and the water quality at the 4 sampling points is inferior to the black odorous water.（2）The average total phosphorus in the sediments upstream and downstream of the discharge outlet is 795.10mg·kg^-1 and 848.32mg·kg^-1,respectively.They were148.72mg·kg^-1and 175.07mg·kg^-1,respectively;the average total phosphorus pollution at the four sites was 1.988,which was severe pollution,and the average total nitrogen pollution was 1.353,which was mild pollution.（3）When no carbon source is added,the average biological and abiotic absorption potentials of the sediments are 0.417,2.950μg·（g·h）^-1,respectively.The potential impact is large,and the effect brought by 250mg·L^-1 sodium acetate is the most significant.In this case,the average value of biological absorption potential is1.247μg·（g·h）^-1,and all sampling points show high abiotic absorption potential.The bio-absorption potential;the non-biological absorption contribution rate of sediment phosphorus is higher than the bio-absorption contribution rate.（4）At the SP1 sampling point,the biological and abiotic absorption potentials of sediment phosphorus are higher than other points at each sampling time,which shows that the more serious the water pollution is,the greater the phosphorus absorption potential of the substrate;the difference analysis It shows that the biological absorption potential is significantly different in the case of adding different concentrations of exogenous carbon,and the degree of difference in indicators in other cases shows a certain degree of complexity.（5）The order of the EPC₀ values of the four sampling points is:SP1>SP2>SP3>CP,which indicates that the wastewater treatment plant effluent discharge increases the river EPC₀ and increases the risk of phosphorus release from the sediment;the addition of external carbon significantly reduces the The EPC₀ value,especially the SP1immediately adjacent to the discharge port,was the most significant.