Control Of Internal Phosphorus By In-situ Passivation Of Lake Sediments And Its Mechanism

Eutrophication of lakes has become a global env Femental issue.Although the exogenous phosphorus(P)is controlled,the release of internal P in the sediment will still cause eutrophication of the lake.Therefore,controlling the release of endogenous P in sediments is the main direction for controlling lake eutrophication.In this paper,the self-developed composite material(La@CSATP),Phoslock? and calcium nitrate are used as passivation materials.Use Rhizon sampler,DGT and PO technology to measure or obtain the dissolved oxygen(DO),SRP,dissolved Fe and available P and Fe change information at the sediment interface with high resolution.The mechanism for controlling internal P was also systematically discussed,in order to provide theoretical guidance and scientific support for the lake management.The main results obtained are listed below.(1)To study the adsorption characteristics of Phoslock? and La@CSATP materials on P in aqueous solution.The results show that materials prepared with different amounts of lanthanum nitrate hexahydrate add different amounts of P adsorption,the adsorption amount:La@CSATP3>La@CSATP2>La@CSATP1.The fitting degree of La@CSATP material Langmuir and Freundlich adsorption model curves are both at a high level.The theoretical saturated adsorption capacity of La@CSATP3 for P is 42.55 mg/g.The adsorption of P by Phoslock? can be well fitted by Langmuir and the kinetic equation.The theoretical saturated adsorption capacity is 13.72 mg/g.When the p H > 9,the adsorption capacity of La@CSATP material and Phoslock? decreases.(2)In a single passivation experiment,Phoslock? coating control overlying water SRP,and significantly reduced the DGT-labile P flux in the surface 0～-20 mm sediment.Phoslock? passivation controlled 54.07% loosely bound P,16.71% Fe-bound P,and 45.33%organic P in the surface 20 mm sediment.La @ CSATP material treatment can also effectively control the overlying water SRP,and can control the SRP at a depth of 25 mm in the sediment.La@CSATP material coverage can reduce loosely bound P,Fe bound P,and organic P in surface sediments by 58.00%,26.19%,and 18.12%,respectively.Phoslock?treatment reduced the content of dissolved heavy metals(Zn,Pb,Ni)in the interstitial water between the overlying water and the surface sediment.In the La @ CSATP treatment group,a decrease in the content of dissolved heavy metals Cd,Cu,Zn,and Pb was observed in the overlying water and the interstitial water at a depth of-25 mm.(3)In combination passivation experiments,the added nitrate content gradually decreases with time,and is removed through the process of denitrification and reduction to ammonia.However,the addition of calcium nitrate left residual nitrate in overlying water and surface sediments.The addition of nitrate nitrogen promoted the nitrogen cycle in the sediment,causing the ammonia nitrogen and nitrite nitrogen concentrations in the interstitial water to rise briefly,and then decreased to lower levels.The addition of calcium nitrate can effectively control the SRP in the overlying water and 0～-50 mm sediment gap water,but it cannot reduce the SRP of the overlying water to the lowest value.Calcium nitrate treatment can reduce the effective P flux in the sediment,but the control effect on the overlying water is not good.Calcium nitrate treatment increased the Fe content in the interstitial water at the depths of-25 mm and-50 mm,but returned to the initial value with the increase of time,and reduced the effective Fe content in the 0～-60 mm sediment.In addition,calcium nitrate treatment can effectively reduce the sulfur flux in the sediment.The combination of La@CSATP material and calcium nitrate can reduce the SRP near 0 mg/L in overlying water and 0～-80 mm sediment gap water,and can effectively control the effective P flux in overlying water.In addition,the addition of calcium nitrate can increase the metal V and As content of the overlying water,but the combined group can avoid this phenomenon.Therefore,it shows that the combination of La@CSATP material and calcium nitrate technology has better application prospects in controlling eutrophication of lakes.