| In view of the important effect of phosphorus on eutrophication of water bodies,two types of vertical-flow constructed wetland systems with natural manganese ores and gravel as the matrix were constructed in this paper.Artificial water allocation was used for wetland water intake.Phosphorus and other water quality indicators in the wetlands of the two groups were constructed separately.Simultaneous monitoring was conducted to examine the removal efficiency of phosphorus and other contaminants from natural manganese ore constructed wetland and gravel constructed wetland.The distribution regularities of phosphorus and related pollutants in two kinds of constructed wetland systems were studied;the phosphorus removal performance and mechanism of natural manganese ore wetland systems were studied.The main conclusions are as follows:（1）Natural manganese ore constructed wetlands and gravel constructed wetlands have obvious differences in the removal effect of phosphorus in sewage.The removal rate of natural manganese ore wetland system is as high as 95%or more and the effluent P concentration in wetland is 0.2 mg/L throughout the research cycle.Reached the first-class discharge standard in the"Emission Standard of Pollutants for Municipal Wastewater Treatment Plants"（GB18918-2002）,while gravel wetland has almost no effect on phosphorus removal.The effluent pH of both wetlands was stable and maintained at a neutral level.The effluent pH of the wetlands in the two groups is between 6 and 9.The removal effect of natural manganese ore wetland on COD is better than that of gravel wetland.The COD of the former is 21.18 mg/L,and the COD of the latter is 40.70 mg/L.In the natural manganese ore wetland,manganese oxides are involved in the degradation process of organic matter.At the same time,the organic matter is removed by oxidation and the corresponding Mn2+is generated.The concentration of Mn2+in the wetland effluent is 0.5mg/L3.0mg/L.（2）In the vertical direction,the wetland water quality has the following distribution characteristics and laws.The pH at the bottom of both wetlands was less than 5,lower than the wetland pH of 7.04,and there was a certain process of anaerobic acid production and H+accumulation at the bottom of the wetland.As the height of the wetland substrate increases,the pH of both wetlands gradually rises to about neutral.COD decreased gradually with the increase of substrate height in the two wetland systems,and the removal rates were all around 90%.The COD removal efficiency of the natural manganese ore wetland system was slightly better than that of gravel wetland.The TP concentration in the natural manganese ore wetland decreases sharply with the increase of the substrate height.Phosphorus is substantially removed in the wet underground half.The outflow TP in the wetland is less than 0.5 mg/L.The TP in the wetland of the gravel wetland system is basically unchanged along the wetland.The regular variation of Mn2+along the vertical direction of wetland in the natural manganese ore wetland system is“first increase and then decrease”.The high-valent manganese ions in manganese ore are reduced to Mn2+into the wetland system,but the adsorption of manganese ore in the upper part of the wetland.Factors such as the adsorbtion,dissolved oxygen oxidation and other factors reduced the Mn2+content of manganese ore wetland effluent.（3）Langmuir isotherm model and Freundlich isotherm model can describe the isotherm adsorption process of natural manganese ore,but the Freundlich model is more suitable（R2=0.9944）.Pseudo-second order kinetics can describe the adsorption process of natural manganese ore.The error between the theoretical saturated adsorption amount and the actual saturated adsorption amount predicted by the pseudo-second-order kinetic equation does not exceed 10%.With the increase of pH,the natural phosphorus removal effect of manganese ore decreased.Increased temperature is conducive to the removal of phosphorus from manganese ore.NH4+,CO32-,and organic matter have essentially no effect on phosphorus removal from manganese ore.When Mn2+alone or Mn2+and CO32-coexist,phosphorus in the water is removed by coprecipitation,and the removal efficiency of phosphorus can reach 95.33%..（4）The main existing forms of phosphorus removed by natural manganese ore adsorption are Fe and Al-P.FTIR,XRD and SEM analysis of the manganese ore matrix of the natural manganese ore wetland before and after reaction showed that the natural manganese ore mainly removes the phosphorus from the wastewater through the exchange of ligands on the surface hydroxyl and phosphate to form the inner layer complex.The natural manganese ore wetland system can remove the phosphorus from the wetland through chemical adsorption and physical adsorption of manganese ore,and it also accompanies the co-precipitation process. |
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