Treatment of Landfill Leachate by Subsurface-Flow Constructed Wetland: A Microcosm Test

摘要

A microcosm test was conducted to evaluate the role of vetiver grass ( Vetiveria zizanioides) and different substrates (including coal refuse, fly ash,cinder, soil and gravel) in purifying landfill leachate collected at Likeng landfill site of Guangzhou City, which contained high levels of COD (1 354 mg/L) and NH_4~+ -N (502 mg/L).The experiment lasted for 75 days with the major findings of present study as follows; 1. The COD removal efficiency of every batch ranged from 33 % to 73 % , NH_4+ -N from 46 % to 74% ,NO_3~--N from 72% to 94% ,TKN from 46% to 73% ,TP from - 127% to 90% , and TSP from -1714% to 92%.2.The wetland microcosm using coal refuse as a substrate had the best performance in removing NH_4 ~+ -N,TKN,TP,TSP and TSS, while the wetland microcosm using cinder as substrate had the best performance in removing COD_3~--NO_3~--N and TSS.3.With the addition of sawdust as a carbon source, the process of denitrification was significantly promoted, however the removal of all compounds except NO_3~--N was inhibited and the growth of vetiver grass was significantly inhibited. The addition of sawdust also led to a reduction in the aboveground, belowground and total biomass of vetiver grass.4. The concentration of NH_4~+-N in leachate greatly influenced the function of vetiver grass in the wetland microcosm.5.Prolonging the HRT can significantly enhance the removal efficiency of NO_(3-)-N. 6. Vetiver grass played an important role in the purification of landfill leachate in the wetland microcosm. The COD, NH_4~ + -N, TKN, NO_3~--N,TP,TSP and TSS removal efficiency of wetland microcosms planted with vetiver grass were greater than wetland microcosms without vetiver grass,9.09%,12.93%,15.72%,104.8%,17.44%,57.02% and 1.61% .respectively.