Treatment Plant Based On Coupled Constructed Wetland In Simultaneous Removal Of Nitrogen And Phosphorus From Tail Water Of Urban Sewage

This study use coupled artificial wetlands to deal with the tail water of sewage treatment plant,to improve the synergistic effect of plants,fillers and microorganisms,form an efficient and mutually nitrogen and phosphorus removal system.The coupled artificial wetlands is constructed by vertical subsurface flow and horizontal subsurface flow in turn.The test chooses hepatic calculus,gravel,and sand gravel as fillers,phragmites australias trin,wild rice stem,acorus calamus as experimental plants.The static adsorption experiments were used to analyze the removal efficiency of nitrogen and phosphorus in the selected substrate.Further,three kinds of adsorption kinetic models were used: first order kinetic adsorption equation,double constant adsorption equation and Elovich adsorption equation were used to simulate the adsorption kinetics of nitrogen and phosphorus.This experiment mainly from two aspects to study the effect of coupled artificial wetlands:(1)The removal rate of main pollutants including ammonia nitrogen,TN,TP and COD;(2)How the pollutant removal rate change when the temperature and pH changes,and then determine the optimal control conditions for constructed wetlands.Through the above method,the test results and conclusions are as follows:(1)The fillers was subjected to a static adsorption test for 48 hours,Divided into four groups: hepatic calculus,gravel,sand gravel and according to a certain ratio,the final removal rates of TP were 25.17%,68.88%,52.35% and 61.56%,the final removal rates for TN were 17.26%,31.07%,23.11%,26.80%.The effect of adsorption on phosphorus and nitrogen sand gravel was higher than hepatic calculus and gravel,the group of according to a certain ratio,had the advantages of sand gravel and gravel,the removal effect of nitrogen and phosphorus is better compared with the sand gravel group,and is more stable.(2)This study chose three kinds of adsorption kinetic models to simulate the adsorption kinetics of nitrogen and phosphorus.Under isothermal conditions,the effect of the three adsorption kinetics models on the removal efficiency of phosphorus was good according to the correlation coefficient.It can be judged that the adsorptionprocess of phosphorus can be influenced by factors such as reaction rate,diffusion factor and other factors.TN has a low correlation coefficient,it represents a low level of significance.Under isothermal conditions,the effect of the three adsorption kinetics models on the removal efficiency of nitrogen was not good according to the correlation coefficient.Considering that nitrogen in artificial wetlands is mainly removed by microbial action,the static adsorption test result verify from the side that the removal rate of nitrogen by matrix adsorption is low.(3)The concentration of pollutants in the effluent from the constructed wetland were COD 5 ~ 12 mg / L,ammonia nitrogen 0.1 ~ 0.5 mg / L,TN 7.5 ~ 20 mg / L,TP0.4 ~ 1.7 mg / L,The effluent values were COD 8 mg / L,ammonia nitrogen 0.3 mg /L,TN 11 mg / L,TP 0.54 mg / L,In addition to In addition to TP can reach the basic level standard,other indicators can be stable to an A standard.(4)In constructed wetland,the temperature change has a certain influence on the removal rate of pollutants,and all of them have positive correlation,the optimum treatment temperature of each pollutant is COD 15 ~ 25 ?,ammonia nitrogen 17 ~22 ?,TN 20 ~ 25 ?,TP 17 ~ 22 ?;The analysis of pH change effect on removal of nitrogen and phosphorus,The removal rate of ammonia nitrogen and TN was negatively correlated with pH,the rule was obvious,the removal rate increased first and then decreased,and the pH decreased first and then increased.TP removal rate was positively correlated with pH,especially from September to October,each inflection point appeared,TP removal rate has the same inflection point,but regular pattern is not so obvious.