The Study Of The Phosphorous Removal In Horizontal Subsurface Flow Wetland Treating The Polluted Surface Water

The study of the phosphorous removal in horizontal subsurface flow wetland treating the polluted surface water was carried out by three steps: (1) Sorption isotherm experiments; (2) Column experiments; (3) Pilot cell experiments.The sorption isotherm experiments results indicated that the P sorption capacity of steel slag, shale, gravel and zeolite, as determined with Langmuir isotherms, were 1666.67mg/kg, 128.21mg/kg, 42.37mg/kg and 56.18mg/kg respectively at 25℃. The amount of phosphate sorbed was increased while temperature was increased, and the amount of phosphate sorbed was increased while the particle size was decreased.The column experiments results indicated that the P sorption capacity of steel slag, shale, gravel and zeolite were respectively 1239mg/kg, 178mg/kg, 40mg/kg and 57mg/kg. This result validated the feasibility of the P sorption capacity determination method by using Langmuir isotherms. The COD concentration restrained the P sorption of the substrate.The pilot cell experiments results indicated that the retained proportion of incoming TP were between 0% and 91% in 3 wetlands. In warm season, the increasing of HRT enhanced the phosphorus removal efficiency. The ideal HRT was 6d for phosphorus removal. The steel slag could not only enhance the phosphorus efficiency and increase wetland life, but also might overcome the disadvantage of the horizontal subsurface flow wetland that the phosphorus removal efficiency was not stable in every season. The phosphorus fractionation of substrate showed that the increasing phosphorus of the different substrates were in the different forms. There was more Ca/Mg-P in gravel (44.80%～68.60%), more residual-P in zeolite (64.99%) and more Fe/Al-P in steel slag(44.38%). The wetland plant harvest was better taken in autumn than in other seasons for phosphorus removal. The multi-plants and the multi-substrates wetland system had the superiority compared with the single plant and single substrate wetland system.