Abstract
In this study constructed wetlands (CWs) were used to remove three heavy metals (Zn, Cu and Pb). The two tested substrates were made of coke and gravel, respectively. First order dynamic model was appropriate to describe removing of Zn and Cu. The experimental results showed that first dynamic removal rate constants of Zn in CWs with coke and gravel were 0.2326 h-1 and 0.1222 h-1, respectively. And those of Cu in CWs with coke and gravel were 0.2017 h-1 and 0.3739 h-1. However, removal efficiencies of Pb in the coke system and the gravel system were within 95-99%, so the first order dynamic model failed to fit the experimental data because the hydraulic resident times of Pb did not affect outlet concentration of Pb. From the removal rate constants, it is found that the coke and gravel system have different absorption efficiencies of heavy metal pollutants. Therefore, it is suggested that the removal efficiencies of heavy metals are influenced by the choice of substrates to some extent.
Highlights
Constructed wetlands have the characteristics of excellent performance, minimal investment and operating cost, remarkable economical and social benefits in treating wastewater
Removal efficiencies of Pb in the coke system and the gravel system were within 95-99%, so the first order dynamic model failed to fit the experimental data because the hydraulic resident times of Pb did not affect outlet concentration of Pb
In order to compare with the treating effect of different substrates, coke with particle diameter of 5-10 mm and gravel with particle diameter of 3-8 mm were packed in the different constructed wetlands (CWs), respectively
Summary
Constructed wetlands have the characteristics of excellent performance, minimal investment and operating cost, remarkable economical and social benefits in treating wastewater. In the past 30 years, Europe and North America had set up several thousand constructed wetlands, but the designs and the operations of CWs are mostly based on statistical data and the empirical formula. The removal mechanism of pollutants [1] is important bases of the engineering designs of the CWs, and can provide reliability of CWs in engineering design and operation. Adsorption may play an important role in the removal process. There has been some recent work that has attempted to investigate the influence of different substrates [3,4]. Those researches mainly focus on the treatment of wastewater containing P and N. There remains a lack of information on heavy metals purification effects in the CWs systems with different substrates
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