Aquatic environment

Effects of Cd2+ and Pb2+ on the substrate biofilms in the integratedvertical-flow constructed wetland

ZHANG Jinlian , CHENG Shuiping , HE Feng , LIANG Wei , WU Zhenbin


Received October 13, 2007,Revised March 10, 2008, Accepted , Available online

Volume 20,2008,Pages 900-906

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The effects of single Cd2+ and Pb2+, and combined Cd2+ and Pb2+ on dehydrogenase activity and polysaccharide content of the substrate biofilms in the integrated vertical-flow constructed wetland (IVCW) were studied. Dehydrogenase activities decreased linearly with the increasing concentrations of Cd2+ and Pb2+ at di erent times (6, 24, 72, and 120 h). The activities at both 6 and 24 h were significantly higher than that at 72 and 120 h in the case of single and combined treatments. The single Cd2+ and Pb2+ treatments significantly inhibited dehydrogenase activities at concentrations in excess of 20 mol/L Cd2+ and 80 mol/L Pb2+, respectively. The inhibitory e ect of Cd2+ was much greater than that of Pb2+. At the same time, the combined treatment of Cd2+ and Pb2+ significantly inhibited dehydrogenase activities at all five concentrations studied and the lowest combined concentration was 1.25 mol/L Cd2+ and 5 mol/L Pb2+. A synergistic e ect of Cd2+ and Pb2+ was observed. On the other hand, polysaccharide contents varied unpredictably with the increasing concentrations of Cd2+ and Pb2+ and extended experimental time. There were no significant statistical di erences within the range of concentration and time studied, whether singly or in combination. These results implied that the e ects of heavy metals on biofilms should be a concern for the operation and maintenance of constructed wetlands.

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