The Pinheiros River, in São Paulo

In 1992, then-São Paulo governor Luiz Fleury made a promise. He said that by the year 2005 he would drink water from the Tietê river, a polluted stream that tears through the city of São Paulo. More than three decades have passed and having clean rivers in the largest city in Brazil is still a pipe dream—one that has cost more than USD 2.7 billion, with very little effect.

The Pinheiros river is an affluent to the Tietê and suffers from the same sanitation problems. Untreated sewage from 2 million people gets dumped there every day; when it rains, the overflow goes straight to the river, helping to make it a smelly postcard of the capital of São Paulo. Only 59% of the sewage that is collected gets proper treatment. That is the equivalent of 660 Olympic pools of waste that go into the many rivers that form the basin every day.

A study by the School of Public Health at the University of São Paulo is hoping to change that in the near future. Engineer Paula Vilela will test the use of nanobubbles to improve the water quality of the Pinheiros river. These bubbles are different from the ones we’re used to seeing in the water. They measure 50 nanometers (0.00005 millimeters), do not float to the surface easily, and can last for several hours or even months. Moreover, they are slower and more stable than common bubbles.

These microstructures are created by a generator which stirs up the water and is able to create hundreds of thousands of tiny bubbles, which are made of air, oxygen or ozone. Ms. Vilela explains that this process does not generate residues nor use chemicals. The nanobubbles, she says, have a lot of energy and are capable of attracting bacteria to them. Then, not being able to move or feed, they die. According to her, this is important because the majority of domestic sewage has organic matter that attracts the micro-organisms. “It destroys bacteria and does not generate waste”, she says.

Bubbles may help increase water supply

In the next two months, Ms. Vilela and her team will set up the equipment necessary for the research to happen. Then, in the following 12 months, they will analyze the water on a weekly basis to measure the method’s effectiveness. Prior tests were “very impressive,” the engineer says. The nanobubbles were able to reduce pollutants, odor and change the color of the water. Also, the oxygen (which is necessary for life to thrive again) stayed in the water for “a long time,” according to Ms. Vilela.

If the experiment succeeds, the objective is to able to pump water from the Pinheiros to the Billings reservoir. The river had its course reverted because it became too dirty to supply water for São Paulo’s residents. Success means removing organic matter and pollutants from the water. “This water could be pumped back to Billings, which greatly increases water availability”, believes the researcher.

How São Paulo killed its rivers

If you live in or have even been to São Paulo, it is likely that you’ve walked over a waterway without even noticing it. There are between 300 and 500 of them in Brazil’s biggest city, running through pipes extending from 1,500km to 4,000km (932mi to 2,485mi). And the fate of the city’s main rivers doesn’t have a happy ending. They’ve become ugly and polluted—like infected open wounds on the surface of an otherwise great city.

But how things have become so bad? The documentary Between Rivers tracks the reasons why local authorities have historically looked at the rivers as a nuisance, as well as how they decided to remove them and open space for cars and buildings.

“The price we are now paying is high. We hide our rivers underground, but every year during the rainy season, we notice their presence in floods,” says director Caio Ferraz. The documentary was released in 2008, and has become a reference in the debate about São Paulo’s hydric resources. This is especially the case in the last two years, when São Paulo, between 2014 and 2015, endured what is arguably its worst hydric crisis to date.

The creators of the movie are also producing a web series about the hydric crisis called Live Volume.

Between Rivers from Caio Ferraz on Vimeo.

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SocietyNov 10, 2018

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BY Diogo Rodriguez

Rodriguez is a social scientist and journalist based in São Paulo.