All it takes are three actions: collect, remove and treat the sewage before releasing it into the river. The recipe is simple, but most countries fail to apply it. A report by the World Water Commission, an international entity linked to the UN, points out that among the 500 largest rivers in the world, more than half face serious pollution problems. In Brazil, the sad example is the Tietê, certainly one of the most polluted rivers on the planet. When it passes through the metropolitan region of São Paulo, it receives almost 400 tons of sewage per day and is considered dead: only organisms that do not need oxygen survive in its bed, such as certain types of bacteria and fungi. The main cause of pollution is domestic sewage. “Almost 5 million people still have their waste dumped directly into the river”, says engineer Lineu José Bassoi, from the Environmental Sanitation Technology Company (Cetesb), linked to the São Paulo government’s Environment Secretariat.
When you dream of cleaning up the Tietê, it is inevitable to think of the Thames, in England. The story of Europe’s dirtiest river in the 19th century began to change in the 1960s, when a system of treatment plants removed almost 100% of the sewage released into the river, which today has fish living along its entire length. The São Paulo case is more complicated. First, because the Thames received less sewage and has a higher flow rate than the Tietê, better diluting the dirt. Second, because Brazilian plumbing uses the absolute separator system: the rainwater collected by the manholes runs in one pipe (rainfall gallery) and the sewage in another. In England, the two systems mix and go together to the treatment plant. “In Brazil, only sewage is filtered. The storm sewer, which goes straight to the river, has a huge number of clandestine sewage connections”, says engineer Antonio Marsiglia Netto, from the Basic Sanitation Company of the State of São Paulo (Sabesp).
One of the solutions to control this filth would be to install treatment stations inside the river itself. Another essential action is to increase the amount of treated sewage, which today stands at 64% in the metropolitan region of São Paulo – tasks that will take at least another 20 years.
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war operation
Cleaning work on the Tietê River, in São Paulo, has several action frontsThe origin of the problem
Tietê suffers the action of three types of pollution: industrial, diffuse (formed by garbage from houses and streets taken by the rain) and domestic sewage, the most harmful of all
protection bars
Part of the sewer system has grates to try to stop the solid waste that goes into the river. Among the waste trapped in the pipes, Cetesb technicians have even found a Beetle
Spy camera
To identify clandestine sewer connections in the stormwater galleries (which collect rainwater), a mini camera walks along the pipe. Every year, 70,000 illegal connections are discovered!
Extra dose of oxygen
One of the best options for removing dirt that falls into the river is the so-called flotation station. At the bottom of the river, a network of tubes injects oxygen microbubbles that make the dirt float, facilitating its removal. An experimental flotation plant, set up on the Pinheiros River (which pumps water into the Tietê), should start operating in the next two months
bed lowering
The 2.5 meter deepening of the Tietê gutter, increasing its depth, aims to prevent flooding. But a greater flow of water also helps with depollution. In addition to sand and earth, the dredgers have already removed more than 85,000 tires from the bottom of the river!
limited filtering
About two-thirds of Greater São Paulo’s sewage passes through one of the five treatment stations in the region before reaching the river. The water that leaves here for Tietê is reuse water – it is used for irrigation and industries, but it is not drinkable
industrial modernization
Mercury, zinc, lead and other heavy metals still appear in Tietê, but in much lower concentrations than in 1992, when the depollution work began. Today, 90% of the 1,250 polluting industries have their own treatment for their chemical sewage.