Experimental Study On Pollution Release Control From Sediment Of Urban Landscape Water Recharged With The Reclaimed Water

Water pollution and the increasing urban water demand make the shortage of water resources a global problem,and people’s high demand for quality of life also makes the area of urban landscape water larger and larger.Therefore,the use of reclaimed water to supplement landscape water has become the choice of northern water-deficient cities.However,the types and concentrations of pollutants in reclaimed water are often higher than those in surface water,resulting in higher pollutant content in the sediment replenished by reclaimed water in landscape water,and long-term operation may become an important pollution source.This study aimed at the problem of endogenous pollution release from sediment of urban landscape water recharged with the reclaimed water,firstly,the best covering material was selected by comparing the control effects of CaO₂composite（C-CaO₂）and its single ingredients covering on endogenous pollution release from sediment.At the same time,the optimal concentration of nitrate（NO₃^--N）was proposed by comparing the control effect of maintaining different NO₃^--N concentration in overlying water on the endogenous pollution release from sediment.Finally,the control effects of the best covering material and the optimal NO₃^--N concentration on the release of endogenous pollution from sediment were compared and comprehensively evaluated.The following conclusions were obtained:1)C-CaO₂ can obviously increase the DO concentration and ORP level in the overlying water,enhance nitrification and inhibit the reduction and release of Fe³⁺in the sediment,so that the concentrations of nitrogen（N）and phosphorus（P）in the overlying water are remarkably reduced.Compared with CaO₂ reactor,the concentration of ammonia nitrogen（NH₄⁺-N）and phosphate(PO₄^3--P)in the overlying water of C-CaO₂reactor were decreased by 50.77%and 64.51%respectively.2)C-CaO₂ can reduce the contents of mobile P(P _mobile)and transferable TN（TTN）in the sediment.Compared with CaO₂ reactor,the content of P _mobile in C-CaO₂ reactor were decreased by 6.07%and 10.30%,the content of TTN were decreased by 4.53%and4.81%at 0-2 cm and 2-4 cm depths,respectively.3)The higher the concentration of NO₃^--N in the overlying water,the better the control effect of sediment endogenous pollution.Compared with N₀ reactor,the average concentrations of NH₄⁺-N and PO₄^3--P in the overlying water were decreased by 72.39%and 83.53%when NO₃^--N concentration was 7.5 mg L^-1 in the overlying water.4)The higher the concentration of NO₃^--N in the overlying water,the more obvious the decrease of the proportion of NH₄Cl-P and Na OH-nr P,and TTN content in the sediment.Compared with N₀ reactor,when the concentration of NO₃^--N was 7.5 mg L^-1in the overlying water,NH₄Cl-P and Na OH-nr P contents in the sediment were decreased by 36.35%and 32.05%respectively,and TTN content were decreased by 13.30%.5)By comparing the control effects of covering C-CaO₂ and adjusting the concentration of NO₃^--N in the overlying water on pollutant release from sediment,the results was shown that both methods can effectively reduce the concentrations of PO₄^3--P and NH₄⁺-N in the overlying water.Compared with CK reactor,the concentrations of PO₄^3--P and NH₄⁺-N in the overlying water of C-CaO₂ reactor were decreased by 86.67%and 69.12%respectively,and those in N_7.5 reactor were decreased by 82.41%and 72.36%respectively.However,compared with N_7.5 reactor,the contents of P _mobile and TTN in the sediment in C-CaO₂ reactor were decreased by 23.27%and 34.35%respectively.