Influence Of Water Source On Sediment And Water Quality Of Landscape Water And In-situ Remediation Of Sediment

In order to solve the problem of severe eutrophication of landscape water supplied by reclaimed water in summer,this study firstly analyzed the seasonal variation characteristics of water quality and nutrient content in sediment through continuous monitoring of overlying water and sediment in different water supply areas of a landscape water body in Xi’an.Secondly,a orthogonal experiment was designed to explore the influencing factors of endogenous release in the landscape water.Then,a series of covering materials were used to in-situ remediate the sediment supplied with reclaimed water,and the optimal material was selected.Finally,the effect of different replenishment periods on the water quality of sediment in-situ remediated under the continuous flow replenishment with reclaimed water was explored,and the dosing mode of remediation was optimized by simulating the reclaimed water replenishment conditions in the actual landscape water.This study can provide an important basis for the eutrophication prevention of landscape water and the pollution control of sediment.The main results and conclusions are as follows:1)The concentration of main pollutants in the overlying water of the reclaimed water supply area is higher than that of the surface water supply area through the actual investigation.Among them,TN,TP,NO₃^--N and Chl-a in the former were 61.96%,23.33%,67.15%and 31.95%respectively higher than the latter.The content of nitrogen and phosphorus in the sediment of the reclaimed water supply area is higher than that of the surface water supply area.Among them,TN,TTN（transferable nitrogen）,NO₃^--N,TP and P-mobile（potentially mobile phosphorus）in the former were 22.06%,134.81%,13.81%,98.24%and 128.26%respectively higher than the latter.Endogenous release is the main cause of water pollution in surface water recharge area while both endogenous release and exogenous pollution are the causes of water pollution in the reclaimed water supply area.2)The main factors affecting NH₄⁺-N release were sediment source,temperature and DO concentration.The main factors affecting NO₃^--N release were sediment source,p H and temperature.The main factors affecting PO₄^3--P release were sediment source,temperature and DO concentration.3)Adding Ca O₂ can effectively repair the sediment and improve the quality of overlying water,and its effect is better than addition of Mg O₂,zeolite and Ca（NO₃）₂.Compared with the control group,the average concentration of PO₄^3--P decreased from 0.15 mg/L to 0.03 mg/L by 78.93%at the dosage of 0.20 kg/m² of Ca O₂.It can also reduce the concentrations of PO₄^3--P and NH₄⁺-N in the interstitial water 3 cm below the mud water interface,effectively stabilize the nitrogen and phosphorus in the sediment,and reduce the risk of nitrogen and phosphorus release in the sediment.4)The addition of Ca O₂ significantly increased p H,DO concentration and turbidity of the overlying water,and rapidly reduced the concentrations of TP and PO₄^3--P in the overlying water in a short time.TP in the overlying water was decreased from 0.10 mg/L to 0.02 mg/L by 80%while PO₄^3--P was decreased from 0.13 mg/L to 0.06 mg/L by 53.84%.5)Compared with the simulated water of 30 d HRT,the decrease rate of p H,DO and turbidity in the overlying water of 15 d HRT with Ca O₂ addition was faster.On the other side,the increase rate of PO₄^3--P and TP concentration was higher in the overlying water of 15 d HRT with Ca O₂ addition than that of 30 d HRT,indicating that the phosphorus locking effect of Ca O₂ was poor in shorter HRT.