Removeal Of Phosphous From Farmland Runoff By Constructed Wetland System

As the increasing of point source pollution harness, the control of no-point source pollution has gradually become the key of inducing outside pollution loading. While the pollution of farmland runoff was an important apartment of farmland no-point source pollution, Input of exogenous phosphorus was a key factor that results in eutrophication of water body of lakes, rivers, ocean, etc. So, the control of phosphorus from farmland no-point source pollution has an important value for preventing pollution and inducing eutrophication risks. Constructed wetland, mainly removal BOD and COD had been used in treating city sewage and rural sewage, as improvement of standards for N and P, the research of constructed wetland gradually turn into TN and TF of sewage. At present,there has manly research about constructed wetland for treating sewage that provided theoretical basis of application and popularization,but there has relatively lacking about treating farmland runoff. Hereby, adsorption characteristic of four kind's filler of constructed wetland was analysised by adsorption of static. The mechanism of removal phosphorus from filler has been researched by the way of dynamics and thermodynamics. The sewage characteristic of farmland runoff has been surveyed and analysised by long term fixed-point monitoring. On this basis, the removal phosphorus from farmland runoff in constructed wetland has been key study by lab research. At the same time, phosphorus treatment in storm runoff has been study by using the way of simulation.The results showed that change of pollute index in farmland runoff has not showed itself a rule, TN in farmland runoff has been constituted by NH4-N and NO₃-N (proportion ratio was 1:1). Solubility phosphorus, account for 88.51%, was a mainly proportion of total phosphorus. The concentration range of TN,NH4-N,NO₃-N,TP,DP was 0.53～12.11,0.30～1.29,0.18～2.67, 0.045～0.688,0.040～0.664mg/L, respectively. According to three standards of GB3838-2002 and taking Nemerrow index as estimate method, the result showed that farmland runoff by blank disposed arrived at little pollution, but farmland runoff by general disposed arrived at badly pollution. So the pollutiton of farmland runoff must be high attention.The behaviors of phosphorus adsorption to substrates can well be fitted to both Langmuir and Freundlich isothermal adsorption equations. The phosphorus adsorption capacity of four substrates followed that limestone (666.67mg/kg)> river sands (500.00mg/kg)> shale (434.78mg/kg) > purples soil (416.67mg/kg).Elovich equations could be accurately fitted for describing absorption characteristic of four substrates (R²=0.831～0.966).The rate of saturated substrates phosphorus desorption followed that river sands (4.257%)> shale (3.803%)> limestone (3.638%)> purples soil (2.134%). the phosphorus adsorption process of four substrates was a spontaneous process (ΔG⁰< 0)-a physical adsorption process. The combined investigation of four substrates showed that limestone was better constructed wetland substrates.Three kinds of constructed wetland could be used reducing phosphorus of farmland runoff, Outlet water quality have attained the standard of III class surface water. As increase of HRT,the ratio of removal phosphorus and system stability of removal phosphorus has been increased,at the same HRT, the effective of removal phosphorus followed that Cyperus alternifolius bed> Canna lily bed> blank bed.The ratio of removal phosphorus and its loading has been fitted by the Linear Equation (y=ax+b) that y₁=0.7881_x1+2.9707 (R²=0.9891),y₂=0.7299_x2+5.1386 (R²=0.9680), y₃=0.6762_x3+6.8917 (R²=0.9469), respectively. The removal phosphorus of constructed wetland colud been fitted by Fist Pushing Kinetics Equation. fist kinetics constant of 3 kinds of constructed wetland were 0.0755,0.0669 and 0.044d^-1, respectively. The dynamic path of removal phosphorus could been fitted by Exponential Equation that y₁= 0.8905e^-0.0181X1 (R²=0.9752) y₂=0.9543e^-0.0171X2 (R²=0.9812),y₃=1.0048e^-0.0157X3 (R²=0.9749),respectively. It could provide thereference of practical project design because of the significant of equation correlation. Constructed wetland colud be effectively used in control pollutant of storm runoff and had a strongly ability of tolerable in shock load. The total phosphorus colud be reduced Cyperus alternifolius bed, Canna lily bed and blank bed in storm runoff. The plant of contructed wetland has an important function during reduce of runoff. The effective of removal phosphorus of constructed wetland showed that Cyperus alternifolius bed> Canna lily bed> blank bed at the average hydraulic loading of 59.733 cm/d, the ratio of removal phosphorus were 57.056%,54.623%,48.232%, respectively. Comparaed to other beds, Cyperus alternifolius bed has better effect. Effluent concentration of phosphorus showed that slowly increase and slowly fallback in the process of storm runoff. The plant has an important function in contructed wetland, for the removal phosphorus, the contribution ratio of Cyperus alternifolius and Canna lily were 11.187% and 14.145%, but the main removal approach is substrates.