Study On Purification Effect And Mechanism Of Functional Floating Bed On Eutrophic Landscape Water

Ecological floating beds（EFBs）are an important way to purify the water quality of eutrophic landscape water bodies,but the conventional EFBs have limited purification capacity and efficiency for nitrogen and phosphorus nutrients,algae and organic matter.Therefore,this study used calcium peroxide and sponge iron to hang together in order to strengthen the EFB to remove nutrients,algae density and organic matter.The research first optimized the best quality ratio of calcium peroxide and sponge iron through laboratory simulation experiments,and on this basis,explored the conversion mechanism of nitrogen in simulated landscape water.Then,the functional floating beds（FFB）suspended with calcium peroxide and sponge iron were used to purify the water quality of a pilot-scale simulated landscape water body,and the effect of the FFB system on the fate of nitrogen and phosphorus nutrients and characteristics of sediment in the water body was explored.The main experiment results and conclusions obtained in this study are as follows:1)The main products of calcium peroxide dissolved in water are oxygen,calcium ions and hydrogen peroxide;the main products of sponge iron dissolved in water are Fe（II）and Fe（Ⅲ）.The combined suspension of calcium peroxide and sponge iron can make the removal rate of phosphorus and algae density in the landscape water reach85.91%and 83.75%,and can effectively reduce the concentration of fulvic acid-like in the water,and at the same time realize the fixation of phosphorus in the sediment.The simulation experiment optimizes the optimal mass ratio of calcium peroxide and sponge iron to be 1:8;it is explored that the removal of phosphorus by the combined filler mainly depends on the precipitation of calcium peroxide on phosphorus and the adsorption of phosphorus by sponge iron.In addition,the H₂O₂ generated by the dissolution of calcium peroxide can generate strong oxidizing OH^·under the catalysis of Fe（II）dissolved from sponge iron.OH^·performs indiscriminate oxidation,which is the main reason for the decrease in algae density and organic matter concentration in the water.2)Calcium peroxide dissolves in water to generate oxygen,which can increase the activities of ammonia monooxygenase（AMO）,hydroxylamine oxidase（HAO）and nitrite oxidase（NOR）to enhance ammonia oxidizing bacteria（AOB）and subunits in surface sediments.The activity of nitrate oxidizing bacteria（NOB）promotes the process of ammonia oxidation and nitrite oxidation,and accelerates the removal of NH₄⁺-N in overlying water.Sponge iron enhances the activity of denitrifying bacteria（DNB）in surface sediments by increasing the activities of nitrate reductase（NR）and nitrite reductase（NIR）,inducing the denitrification of microorganisms in the system,and accelerating the denitrification of the system,and calcium peroxide and sponge iron have a synergistic effect on denitrification.At the same time,the hydrogen peroxide generated by calcium peroxide can effectively degrade organic nitrogen in water,and the Fe（Ⅱ）eluted from sponge iron can react with the hydrogen peroxide eluted from calcium peroxide to form a Fenton-like reaction to generate hydroxyl free radicals and aggravate the organic nitrogen degradation.3)The suspension of calcium peroxide and sponge iron can improve the purification efficiency of the EFB on the water quality of the reclaimed water replenishing the landscape water.Among them,the removal rate of TN,NH₄⁺-N,NO₃^--N,TP,PO₄^3--P,COD and algae density can reach 59.8%,52.4%,54.72%,89.09%,93.94%,44.33%and 66.41%.The FFB can maintain the nutrient level in the water body at the mesotrophic level（chlorophyll a≤10μg/L）,effectively avoiding the occurrence of eutrophication in the water body.At the same time,the FFB can effectively reduce the concentration of humus-like substances in the water,and can eliminate the risk of secondary pollution of pollutants in the water after plant decay.4)Plant absorption is the main way to remove nitrogen and phosphorus nutrients.The removal of nitrogen in the system can reach 11.58%,and the removal of phosphorus can reach 16.07%.In the selection of FFB plants,Lythrum chinensis and coingrass are preferred,and its can maximize the absorption of plants.At the same time,the suspension of the filler in the FFB can make the plant root microbial community more stable,and can significantly increase the heterotrophic denitrification of root microbes,the autotrophic and heterotrophic denitrification-related abundance of microbes induced by sponge iron.In addition,the nutrients in the FFB system are mainly concentrated in the sediments,and the suspension of sponge iron and calcium peroxide can change the proportions of N and P in the sediments,making them more stable.Finally,the N and P adsorbed by the sponge iron in the FFB at the end of the test accounted for 2.43%and 3.04%of the TN and TP in the system,respectively.