The Development Of Phosphate Anion Barrier(PAB) And Interception Of Internal Phosphate Pollution In Eutrophic Water Bodies

Eutrophication of water bodies is a difficult challenge in environmental protection.As is all known,the eutrophication is always caused by the excessive load of nitrogen and phosphorus in surface water bodies.In order to control the nutrient concentration in surface water bodies,the discharge of phosphorous to aquatic system was limited all over the world.However,the situation of eutrophication has not been relieved,even more seriously.Some researchers have shown that the internal nutrient pollution played an important role during this process that phosphorus were continuously released from a large number of lake sediments to overlying water,which worsen the eutrophication of the water bodies.Therefore,the controlling of internal nutrient pollution must be considered.Therefore,sediment dredging is developed to permanently removing the sediment for reducing the phosphorus release.Also,Phoslock? was developed to inactivate the phosphorus in the lake to relieve eutrophication.However,these two methods have vital defects.Sediment dredging is high cost,controversial and opponents that sediment dredging can only temporarily alleviate the pollution,but possibly produce a long-term impact on lake ecosystem.Phoslock? exhibited difficulties in actual application in replace and duration of positive effect.Against this background,this study tended to design and develop a new material,the phosphate anion barrier(PAB).Lanthanum modified graphene oxide(La-GO)is employedas the main functional material,and chitosan-PVA is used as the framework material.La-GO could well distributed and dispersed in framework material.Covering PAB on the sediment,phosphate released would be immobilized by PAB,and finally converted to inactivated phosphorus.Firstly,the graphene oxide(GO)was successfully prepared by the modified Hummers method.Then,the La-GO was coagulated and modified simultaneously by lanthanum.During the La-modification,La3+ combined with hydrophilic functional groups on the surface of GO,formed functional sites.Also,the hydrophilicity of GO was reduced that La-GO could easily be separated from aqueous solution.The experimental results showed that La-GO is highly effective in phosphate removal.The adsorption process well fitted with the Langmuir adsorption isotherm model.The maximum adsorption capacity achieved141.38mg/g.The adsorption kinetics process could be well described by pseudo-second-order equation,and the optimal contact time is less than 20 minutes.In addition,the adsorption process is endothermic that higher temperature is positive to the adsorption process.The reaction process was also affected by different solution p H,in which the adsorption effect is better under neutral and alkaline conditions.The removal of phosphate by La-GO is an adsorption assisted precipitation process:(I)the phosphate ions was reacted with lanthanum on GO,and(II)the resultant precipitates was adsorbed by GO.The resultant La-GO was used to develop the phosphate anion barrier(PAB)with chitosan and PVA.The phosphate interception capacity of PAB was evaluated.The results showed that the La-GO uniformly distributed and dispersed in PAB.Porous was well developed in PAB that caused considerable permeability.The phosphate adsorption isotherm of PAB fitted Langmuir adsorption isotherm model and Freundlich isotherm model well.The kinetics is fitted with pseudo-second-order,Elovich and W-M kinetic models.The adsorption process of phosphate is a multi-mechanism chemical process.In addition,the optimum contact time is approximately 100 minutes.Under the p H condition of 2 and 12,the adsorption capacity is largely decreased,and the adsorption performance is desirable under weak acidic,neutral and weak alkaline conditions.Finally,the PAB was used to evaluate its interception capacity on internal phosphate pollution in a simulated eutrophication condition.The results showed that PAB could well intercept the phosphate release from sediment when PAB was covered on the sediment,and phosphate could not be monitored in overlying water.It could be concluded that PAB is effective in intercepting phosphate release from sediment to overlying water.The results of this research supplied new method,material and experience,that PAB can be seen as a promising material for controlling the internal phosphate pollution in surface water bodies.