Abstract:Through establishment of surface flow constructed wetland system, to study the purification effects of 11 aquatic ornamental plants on COD(chemical oxygen demand),TN(total nitrogen),NH+4-N(ammonia nitrogen) and TP(total phosphorus) under different hydraulic retention time(HRT=3,8,13,18 d).The results showed that the removal rate of each pollutant by 11 aquatic plants was generally higher than that of non-plant control.The average removal rates of COD,TN,NH+4-N and TP were 78.89%-89.26%,90.49%-97.96%,93.24%-98.86% and 86.52%-94.88%,respectively.The water quality indexes reached the standard of surface water environmental quality standard(GB3838-2002).The four pollutants showed a rapid decrease trend in the early stage of operation, the removal rate reached a high level with the increase of HRT and remained relatively stable.Among them, Cyperus alternifolius had better removal effect on COD,Acorus calamus and Thalia dealbata had better purification effect on TN and TP,and Pistia stratiotes had the highest purification rate of ammonia nitrogen.The results of entropy method showed that the comprehensive purification effect of A.calamus was the strongest, while the purification ability of Canna indica was relatively low.