[Analysis on the removal efficiency of phosphorus in some substrates used in constructed wetland systems].

Constructed wetlands are widely used to purify wastewater in some developing countries. As filter substrates in such wetland, these substrates play important role on removal of pollutants from wastewater. Selecting suitable substrates is one of the effective ways to improve the performance of constructed wetland on treating wastewater. In this study the phosphorus adsorption capacities of sand, zeolite, vermiculite, two clay soils, two industrial by-products named steel slag and fly ash are examined for their potential use as substrate in constructed wetland. Both Freundlich and Langmuir adsorption isotherms are very fit for describing the adsorption characteristics of these substrates. Two industrial by-products including steel slag and fly ash have higher phosphorus adsorption capacity, which had 50490 and 17934 mg x kg(-1) respectively. Followed vermiculite, two clay soils named yellow cinnamon and xiashu loess with phosphorus adsorption capacity of 3473, 1893.7 and 1582 mg x kg(-1) respectively. The zeolite and sand had the least phosphorus adsorption capacity with 813.7 and 302 mg x kg(-1) respectively. The experiments on purifying phosphorus from synthesize domestic sewage using these substrates also demonstrate this conclusion. The ability of removal phosphorus of these substrates have closely relationship with their makeup and chemical properties such as pH, total calcium and reactive calcium, reactive Fe, Al including poorly coastal and amorphous Fe, Al oxide. The steel slag and fly ash with higher reactive Ca, such as calcium oxide, have better adsorption capacity of phosphorus than other substrates, and the substrates which contained more reactive Fe also have a better ability of adsorption phosphorus than others. To assess the environmental risk for using these substrates above, the phosphorus de-sorption characteristics of these substrates are also studied. The process of phosphorus desorption quickly reached equilibrium in no more than 4 hours in the experiments, the ratio of desorption and adsorption of phosphorus in substrates above is lower except sand. To take suitable measures to manage substrates above, the risk of pollution of phosphorus form these substrates will be controlled.