Screening And Removal Effect Of N And P By Constructed Wetland Substrates In Cold Region Lakes

Constructed wetlands have been widely used to remove pollutants in water due to their high efficiency and economic advantages.As one of the important components of the constructed wetland,the substrate plays an important role in the constructed wetland system.The characteristics of the the long lake ice seal period and contaminants gradually accumulate in the water under the ice during the ice-sealing process in cold regions.Combined freeze-concentration technology and constructed wetlands,adjust the composition and ratio,analyzed and compared the effects of nitrogen and phosphorus removal in constructed wetland substrates.The best combination ratio of nitrogen and phosphorus was screened out,fully utilize natural cold energy.It can greatly improve the treatment efficiency of pollutants in constructed wetlands and at the same time reduce the operating costs of constructed wetland systems.The characteristics of ice in the frozen period of lakes in cold regions are that the pollutants in the lake water gradually accumulate in the water under the ice during the ice-sealing process,and the concentration of nitrogen and phosphorus in the overlying water can be 4-9 times higher than that in the ice.Turbidity can be 6-11 times higher,and the concentration of heavy metals in the overlying water is 5-16 times higher than that in the ice.In this paper,six kinds of constructed wetland substrates were used to carry out static adsorption experiments through isothermal adsorption models,and their adsorption characteristics for nitrogen and phosphorus were investigated.Through the kinetic adsorption experiments,three kinds of substrate with better adsorption effect were selected for combination.Study on the adsorption capacity of nitrogen and phosphorus by combination.The effects of ambient temperature,influent concentration and particle size on the adsorption characteristics of nitrogen and phosphorus were investigated by kinetic adsorption experiments and thermodynamic analysis.Finally,combine the freeze concentration and adsorption column,obtain the system comprehensive removal rate of nitrogen and phosphorus.Static adsorption experiments showed that adsorption efficiency of ammonia nitrogen on the six substrates was:zeolite>biological ceramic>limestone>ceramic filter>shale>coarse sand.The phosphorus adsorption efficiency was as follows: zeolite>ceramic filter>limestone>biological ceramic>shale>coarse sand.The Langrnuir equation can better describe the adsorption isotherm characteristics of ammonia nitrogen by bioceramic than Freundlich equation,the other five substrates are more accurate described by the Freundlich equation,correlation coefficient exceeds0.98.Both the Langmuir and Freundlich equations can well fit the isothermal adsorption characteristics of six substrates for phosphorus,correlation coefficient exceeds 0.95.Kinetic adsorption experiments showed that when the combination of zeolite:Bioceramic:Limestone was 3:1:1(FSH311),the removal rate of ammonia nitrogen was the highest 94.61%,which was 12.92% higher than the zeolite.When the combination of Zeolite:Ceramic filter:Limestone was 3:1:1(FTS311),the removal rate of phosphorus was the highest 65.65%,which was 11.98% higher than the zeolite.Kinetic experiment of influencing factors and thermodynamic analysis shows that the adsorption of nitrogen and phosphorus by the combination substrate was spontaneous.The concentration of FSH 311 in the process of ammonia nitrogen adsorption has the most obvious influence on the first and second order kinetic constants.In the process of adsorption of phosphorus by FTS 311,the temperature has obvious influence on the first-order kinetic constant and the concentration has obvious influence on the second-order kinetic.Dynamic adsorption experiments show that The pseudo-second-order kinetic model is more accurate than the first-order kinetics simulation in describing the adsorption process of nitrogen and phosphorus in the combined substrate,and the correlation coefficient is over 0.95.Simulated equilibrium adsorption of ammonia nitrogen with temperature changes,the first-order kinetic equation is better.However,the pseudo-second-order kinetics is more accurate when the influent concentration and particle size change.The first-order kinetics is more accurate when simulating temperature changes and the equilibrium adsorption capacity of high-concentration phosphorus-containing wastewater.The pseudo-second-order kinetics has better equilibrium adsorption capacity when simulating particle size changes.The dynamic adsorption column experiment showed that removal rate of ammonia nitrogen was 31%,phosphorus was 34% in the water of Wuliangsuhai.After freezing and concentrating the lake into a column of adsorption,ammonia nitrogen removal rate was 26%,phosphorus removal rate was 30%.The removal rate decreases less,can reduce water inflow and prolong the life of the substrate.Increasing the concentration of influent water increases the adsorption of the substrate,which can effectively reduce the floor space and construction costs when constructing a constructed wetland.