Purification Effect of Vertical-Flow Constructed Wetlands with Multi-Size Combined Filter Medium

Three columns filled with multi-size combined medium were utilized in the simulative vertical-flow constructed wetland systems to treat wastewater at hydraulic loading rate of 2000-3000 mm/d, that the same kind of media including biological ceramsite, anthracite and zeolite in each column. Comparative analyses were made in treatment performances between multi-size medium and single medium. The results showed that compared with the treatment performances of single medium, the purifying effect had great influence by the multi-size combined medium which were made up of same kind and different size of filter medium. Contrast with the corresponding single medium, the average removal efficiencies of COD_Cr, Total Nitrogen (TN), and Total Phosphorus (TP) were increased obviously which were purified by the multi-size combined medium. Good performances were achieved in terms of removal of BOD₅ and COD_Cr in the column of multi-size combined biological ceramsite medium. The average removal efficiencies of TN were great in the column of multi-size combined zeolite medium. Good performances were also achieved in terms of removal of TP in the column of multi-size combined anthracite medium.