Modeling the purification effects of the constructed Sphagnum wetland on phosphorus and heavy metals in Dajiuhu Wetland Reserve, China

Abstract

Wetlands play a significant role in the dilution of contamination, purification of wastewater, and the transformation of toxic substances. In the Chinese Dajiuhu Wetland Reserve, a simple and practical simulation box was used to examine the purification effects of a simulated Sphagnum wetland (SW) on phosphorus (KH2PO4) and bivalent metal ions (Cd2+, Cu2+, Pb2+, and Zn2+) at four different concentrations (20, 40, 80, and 160mgl−1). The modified pseudo-first order kinetics model (Model I) and the pseudo-second order kinetics model (Model II) were used to simulate the purification effect. The results indicated that the purification ability of the SW was remarkable for all of the contaminants; 80.8–98.3% of phosphorus, 71.0–85.4% of Zn2+, 96.8–99.3% of Pb2+, 93.9–99.8% of Cu2+, and 81.4–96.9% of Cd2+ were removed from contaminated water after 2h. The time required for the heavy metal ions to reach equilibrium had a significant positive correlation with their initial concentrations (p=0.004–0.048<0.05), whereas the correlation was poor for phosphorus (p=0.308>0.05). The dilution effect of the SW played an important role during the first 5min; average contribution ratio of dilution effects (CRDE) value of each contaminant ranged from 43.0% to 77.4%. Model II had a better quality of fit than Model I based on the correlation coefficients and the average relative deviation between the purification ratio at the 120th minute (PR120) and the purification ratio calculated by the model at the 120th minute (PR120,c). Empirical formulas for predicting the purification ability of the SW were derived using the parameters of Model II, which could be used for evaluating the purification value of the SW and for providing the scientific basis for the protection and proper utilization of the Dajiuhu Sphagnum wetland.