Emission of trace elements and retention of Cu and Zn by mineral and organic materials used in green roofs
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The increasing surface area of green roofs (GR) may have a significant impact on the quantity and quality of urban drainage. However, the chemical quality of effluents produced by GR in comparison to atmospheric deposit and other roof surfaces has to date been poorly assessed. It is necessary to determine whether a green roof acts as a sink or source of pollutants. This work was conducted to study the capacity of four materials commonly used to build green roofs.
Materials and methods
Leaching tests experiments were performed on three substrates and one drainage material. Sorption kinetics and isotherms were also established for Cu and Zn thanks to batch experiments.
Results and discussion
Results showed the variability of release according to the material and pollutant considered. The equilibrium time for adsorption was high (5 h to 3 days) for all materials. Expanded clay was identified as the material with the highest ability to retain Zn and Cu; also, desorption was limited with this drainage material. In the substrates, Cu was mainly sorbed by organic materials, which induce an important desorption rate due to organic matter leachability.
In conclusion, the study showed that the effect of green roofs on water quality is strongly dependent on the materials used. That is why a characterization of the leaching and sorption capacities of materials should be carried out prior to green roof construction in a context of storm water quality management.
KeywordsGreen roof Kinetics Leaching Metal Sorption isotherms Water quality
A multidisciplinary project has been launched in Nancy (France) with a wide partnership of academic and industrial actors (BATEC Lorraine, Végétoit, Saint-Gobain Weber Portugal, Falienor-Terreaux de France, Nidaplast, Comptoir du Bâtiment, Jardin Botanique de Nancy, association Floraine and Plante & Cité) to evaluate simultaneously the impact of GR on biodiversity, thermal isolation and rainwater quality.
We thank the Research and Innovation Direction of the French Ministry of Ecology, Ifsttar, Cerema and GEMCEA, which provided financial and technical support for this project. Thanks to Marie-Christine Gromaire (LEESU) for her feedback and advice.
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