The Screening And Phosphorus Adsorption Mechanism Of Substrates In Constructed Wetland

In recent years,soil erosion was serious in Xiangxi River Basin.Large amount of nitrogen and phosphorus directly flowed into Xiangxi River with soil and water,leading to the high concentration of nitrogen and phosphorus and frequent algal bloom in Xiangxi River.This situation had a huge negative impact on local people's production and life.Compared with traditional sewage treatment technology,constructed wetland had a lot of advantages such as effective treatment,low costs,landscape aesthetics,etc.It has been widely used in non-point source pollution governance.Substrates play an important role in removing the nitrogen and phosphorus as an important component of constructed wetland.According to the characteristics of the runoff of Xiangxi River watershed,this thesis studied the removal of nitrogen and phosphorus by adsorption onto several substrates and chose the the effective one.Then the research studied the effect of several chapters on the nitrogen and phosphorus removal.In addition,phosphorus adsorption mechanisms were explored through the research.The main conclusions are as follows.(1)Isothermal adsorption experiments showed that,both the Freundlich and Langmuir equation could well describe the ammonia nitrogen and phosphorus adsorption of four substrates.The order of the capacity of ammonia nitrogen adsorption was as followed,zeolite > shale > limestone > gravel.The order of the capacity of phosphorus adsorption was as followed,limestone > shale > gravel > zeolite.The experiments of adsorption kinetics showed that the Elovich equation and the second-order kinetic equation could be more accurate to describe the ammonia nitrogen and phosphorus adsorption kinetics than the first-order kinetics.The second-order kinetic equation was the best one among three equation.(2)The static adsorption experiment showed that,zeolite was the best one to remove ammonia nitrogen among four substrates.The order of ammonia nitrogen adsorption was as follows,zeolite > shale > limestone > gravel.The mass ratio of 1:2 between Zeolite and shale had the strongest capacity of ammonia nitrogen adsorption.Limestone was the best one to remove phosphorus among four substrates.The order of phosphorus adsorption was as follows,limestone > shale > gravel > zeolite.The mass ratio of 2:1 between limestone and shale had the strongest capacity of phosphate adsorption.(3)The higher initial solution concentration and the smaller substrate could both increase the ammonia nitrogen and phosphorus adsorption capacity.When pH was 8,the ammonia nitrogen adsorption capacity reached a maximum,when pH was more than 8 or less than 8,the ammonia nitrogen adsorption capacity decreased.When pH value was at 7~8,the phosphorus adsorption capacity of limestone reached a minimum.When pH was less than 9,the composite matrix phosphorus adsorption capacity had little change,when pH was more than 9,the phosphorus adsorption capacity increased slightly.The competition between nitrogen and phosphorus ion was not obvious.Four organic materials caused the inhibition of the ammonia nitrogen adsorption,but had a complicated impact on the phosphorus adsorption.(4)The physical adsorption was the main mechanism for phosphorus adsorption on zeolite,gravel,shale.The mechanism of phosphorus adsorption on limestone was chemical adsorption,the main phosphorus forms were Ca-P.