Study On Purification Efficiency Of Coal Mine Sewage In Constructed Wetlands

Unique purification mechanism and function of constructed wetland systems make itself has a good ability of wastewater purification.Constructed wetland is gradually widely applied in purification of wastewater due to its advantages of low cost,low-energy and easy to manage.On the basis of reading the literatures on constructed wetland systems,this paper designed 3 kind of outdoor test equipment of the constructed wetland system.Doing relevant research and exploration mainly for screening of plants,treatment effect of three different structures of constructed wetland on mine drainage.The conclusions is as following:(1)The indoor plants screening test showed that different plants has different effect on treating mine drainage.Epipremnum aureum has the best comprehensive treatment effect on pollutant,followed by Hydrocotyle vulgar,and Nelumbo nucifera is the worst.Hydraulic retention time showed the characteristic of ascending slightly prior to declining intensively on plants purified pollutant,the time of water maintained in wetland not the longer,the better will be,there is a best hydraulic retention time For COD,Pb,Cu and Cd,the optimal hydraulic retention time was 4 days,but for the purification of TN and TP,the optimal hydraulic retention time was 6 days.(2)The result of outdoor simulation test showed that the average COD removal rate of three different kinds of constructed wetland systems:composite vertical flow constructed wetland,subsurface flow constructed wetland,and surface flow constructed wetland were 72.3%,63.9%and 49.5%respectively.The average TN removal rate were 71.2%,62.78%and 48.77%respectively.The average TP removal rate were 60.45%,53.15%and 37.41%respectively.The average Pb removal rate were 80.66%,77.80%and 63.81%respectively.The average Cu removal rate were 73.47%,70.25%and 58.90%respectively.The average Cd removal rate were 67.50%,56.64%and 47.51%respectively.The average SS removal rate were 78.47%,72.30%and 62.91%respectively.In summary,the composite vertical flow constructed wetland system and flow constructed wetland has the better effect on the removal of various pollutants than surface flow constructed wetland.It shown that the structure of the composite vertical flow constructed wetland and the structure of the subsurface flow constructed wetland are superior to the structure of the surface flow constructed wetland system and can better remove the pollutants in the sewage.The heavy metal migrates and deposits with the flow of the constructed wetland system,and thus accumulates in the matrix of the constructed wetland system.Therefore,different forms flow of water lead to the different distribution of in the heavy metal in constructed wetland.