Nutrients Transfer in Subsurface-Flow Constructed Wetland

A two-stage subsurface-flow constructed wetland (SSFCW); combined with horizontal flow constructed wetland (HFCW) and vertical flow constructed wetland (VFCW) was established to investigate nutrients transfer in the carriers and the macrophytes. Under average temperature of about 24.8degC, the system operated in the hydraulic load of 0.3~0.4m³m^-2d^-1 and six dominant natural macrophytes conditions for eight months. The results demonstrated with horizontal direction of HFCW, the concentration of total nitrogen (TN) and total phosphorus (TP) decreased dramatically, and the correlation of nutrients and organics was significantly positive both in terms of nutrients concentration and the ratio of nutrients/MLSS. At vertical direction, from 5~15 cm to 55 cm, the nutrients concentration were obviously removed in HFCW and VFCW (260 mg (dm^-3) and 510 mg (dm^-3) of TN decrement as well as 340 mg(dm^-3) and 750 mg(dm^-3) of TP decrement). With the exception of TP rebound occurred in the bottom of HFCW. On the other hand, the distribution of TN in macrophytes was depended on the differences of the plant´s organ and growing phase. The concentration of TN was higher in tender organs and seeds than in caudex and pedicel. The concentration of TP was greatly correlated to the species of macrophytes. Environmental conditions induced the change of TP transformation.