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In São Paulo City, Brazil, the Tietê River is polluted by a vast amount of waste, mainly domestic sewage, but the farther it runs into the interior, the better the quality of its water becomes. It is much less murky at Barra Bonita, 294 km from São Paulo, and transparent at Buritama (546 km).
A study by Brazilian researchers at São Paulo State University (UNESP) in Presidente Prudente and São José dos Campos shows that this change in water quality as the river crosses the state is due to filtration by a series of dams along the way. The 1,100 km Tietê rises near the coast, passes through the state capital and flows on to São Paulo's western border, where it joins the Paraná, a tributary of the Plata. The Barra Bonita reservoir retains part of the algae that feed on nitrogen and phosphorus in the sewage. With fewer of these organisms, the river flows through the turbines and on to the next set of dams, where it is filtered again.
Study - Shows - Filtration - Tietê - Series
As the study shows, filtration of the Tietê by this series of dams allows more light into the water, which is oxygenated and converts more organic matter from pollutants into inorganic matter, eventually becoming transparent. The results were published in the journal Water.
"We demonstrate that Tietê water quality steadily improves thanks to this reservoir cascade, with exposure to pollution from domestic sewage decreasing as the river flows away from the state capital," said Enner Herênio de Alcântara, a professor at UNESP in São José dos Campos and one of the authors of the study.
Reservoir - Composition - Matter - River - Changes
"From one reservoir to the next, the composition of the organic and inorganic matter in the river changes. This affects light absorption in each reservoir," Alcântara told.
The researchers analyzed the light absorption characteristics of the water in four...
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