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| Author(s): |
José Ângelo Sebastião Araujo dos Anjos
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Escola Politécnica (EP/BC) |
| Defense date: | 2003-02-24 |
| Examining board members: |
Luis Enrique Sanchez;
Maria Eugenia Gimenez Boscov;
Sergio Medici de Eston;
Elton Gloeden;
Lucedino Paixão Ribeiro
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| Advisor: | Luis Enrique Sanchez |
| Abstract | |
A lead ore smaller which operated from 1960 to 1993 in Santo Amaro da Purificação, Bahia State, disposed of 490,000 tons of slag in a landfill situated in the situated in the industrial site. Earthworks formed a man-made wetland downstream of the slag landfill, which acted as a metal retaining systems, thus preventing further water pollution. This research aimed at investigating the efficiency of this wetland as a water pollution control system. The research plan scheduled weekly samplings of rainfall, rainwater pH and water runoff in two points corresponding to the input and the output of the wetland for determination of metals concentration (Pb, Cd, Cu, Zn, Al, Mn, Fe, Mg, Ca), as well as water pH, Eh, conductivity, temperature and dissolved oxygen (OD). In addition, soil and sediment in the wetland were sampled and analyzed for Pb, Cd, Zn and Cu by sequential extraction methods. However, a Court ruling following a lawsuit for environmental damage led to the slag being covered by clayish soil weeks after sampling began. As a consequence, the point where waters entered the wetlands has been covered. Hence, sampling in this point has been discontinued and a new sampling point was established downstream of the wetland, at a point where its waters flow into a river. Results showed that before cover-up, Pb, Cd, Cu and Zn were being retained in the wetland at rates reaching 100% for Cu and Zn, 82% for Pb and 73% for Cd. After cover-up, Cd was being released into the waters. Sequential extraction showed that only Cu is not available for leaching, since it is mostly concentrated in the insoluble phase. On the other hand, Pb, Cd and Zn are potentially available, thus could re-enter other media if wetland is disturbed. The wetland acts as an efficient device for retaining metals because of near neutral water pH, oxidizing water Eh, and the existence of montmorillonite clay in the sediments, which features high cationic exchange capacity. It is concluded that this involuntary wetland has been working, as an efficient system for water pollution control. The reduction in its size, due to the cover-up activities, is undesirable. Hence, a new constructed wetland is proposed downstream of the existing one. Then, we can end that the wetland of Plumbum this being efficient in the control of the metals, from when interferences anthropogenetic that maximize the capacity of support of this system dont happen. (AU) | |