Comparison between Horizontal Subsurface-flow and Vertical-flow Constructed Wetlands for Treatment of Jiyun River Water

To improve the water quality of Jiyun River to class Ⅳ criteria specified in Environmen-tal Quality Standards for Surface Water(GB 3838-2002),horizontal subsurface-flow and vertical-flow constructed wetlands were built on empty area in the north bank of Jiyun River to investigate the purifica-tion effect.The raw water from Jiyun River was pretreated by air flotation before entering the system to prevent phytoplankton clogging the packed bed.When PAC dosage is 50 mg/L,the removal rates of COD,BOD5,SS,TN,NH3-N and TP in the horizontal subsurface-flow constructed wetland are 65%,50%,100%,70%,90% and 65% respectively,and those in the vertical-flow constructed wetland are 45%,70%,100%,65%,95% and 85% respectively.The effluent quality of both constructed wet-lands can reach the class Ⅳ criteria.However,considering that the packed bed of vertical-flow construc-ted wetland freezes during winter,the horizontal subsurface-flow constructed wetland is suggested to treat Jiyun River water.