Wang L.-S.,Xian Water Group Co. |
Zhang Y.-N.,Xian University of Technology |
Zhu W.-H.,Xian University of Technology
Xi'an Jianzhu Keji Daxue Xuebao/Journal of Xi'an University of Architecture and Technology | Year: 2010
The Tangyu Reservoir is the main drink water source for Xi'an city. The research on the pollution characteristics and the assessments of the potential ecological risk of the heavy metals(Cd, Zn, Cr, Ni, Cu and Pb) in the superficial sediment seems necessary. The results showed that the concentrations of the six heavy metals are lower than that of the background values in lake sediment in China. The speciation of the heavy metals in the superficial sediment were investigated by the BCR sequential extraction. The potential ecological risk index () of Cd in the superficial sediment is higher than other heavy metals. The sequential extraction experiment showed that the main speciation of Pb in sediment was the reducible fraction. In addition to the residue fraction, Cd existed in the sediment mainly as the form of dissolvable and exchangeable fraction which could be more easily transferred from the sediment to the overlying water. The study of the influence of the redox condition on the heavy metal speciation shows that the environmental behavior of Cd, Cr and Pb was strengthened, while it was opposite to that in the reduced condition.
Ren Y.-X.,Xian University of Architecture and Technology |
Zhang H.,Xian University of Architecture and Technology |
Wang C.,Xian University of Architecture and Technology |
Yang Y.-Z.,Xian University of Architecture and Technology |
And 2 more authors.
Journal of Environmental Science and Health - Part A Toxic/Hazardous Substances and Environmental Engineering | Year: 2011
The depth of substrate in constructed wetlands (CWs) has a significant effect on the construction investment and the purification performance of CWs. In this study, a pilot scale CW system was operated in a domestic sewage treatment plant in Xi'an, China. The experimental systems included three-series CWs systems with substrate depths of 0.1m, 0.3 m and 0.6 m, respectively. Each series was composed of a hydroponic ditch, a horizontal subsurface flow CW and a vertical flow CW. The effluent from the primary clarifier in the sewage treatment plant was intermittently conducted to the wetlands at a flow rate of 0.3 m3/d. The hydraulic loading rate of each CWs system was regulated at 0.1 m3/m2.d and the hydraulic retention time was 3 days. Canna indica L. was planted both in the hydroponic ditches and the CWs systems. Results showed that the highest removal efficiency of NH + 4-N and TP was obtained in the hybrid CW with 0.1 m substrate depth. The average removal efficiency for NH+ 4-N and TP were 90.6 % and 80.0 %, respectively. The highest average removal efficiency of COD was obtained in hybrid CWs system with 0.6 m substrate depth. Therefore, a simultaneous removal of COD and nutrients can be achieved through the combination of different wetlands using different substrate depths. In addition, the substrate depth presents significant effects on the concentration of DO and root growth characteristics of canna in the system. As a result, the highest concentration of DO (>2 mg/L) and the highest amount of roots production were achieved in the 0.1 m substrate depth horizontal and vertical flow CWs. Copyright © 2011 Taylor & Francis Group, LLC.