Depollution of Guanabara uses technique from the Pinheiros river – 03/21/2024 – Environment

Águas do Rio, the main sanitation concessionaire in Rio de Janeiro, began testing at the end of last year with technologies used in the Pinheiros River cleaning project to accelerate the depollution of Guanabara Bay.

Since November, the company has been using the Pavuna sewage treatment plant to clean up the river of the same name, a strategy used in the recovery units used in São Paulo. In January, it also started injecting oxygen into the Joana River, in Tijuca, to reduce the organic matter generated by the release of sewage.

The two strategies are auxiliary to the main depollution strategy in Rio de Janeiro, just as they were in São Paulo. They are part of the total budget of R$2.7 billion for the project.

Águas do Rio has until 2026 to stop the release of waste into the water bodies that flow into Guanabara Bay through so-called dry weather collectors. They have this name because they only operate on days without rain, using the rainwater network to route sewage to treatment plants.

The concession contract also provides for the expansion of the exclusive sewage network to 90% of the population by 2033.

Such as Sheet showed in September, the construction of dry weather collectors is delayed due to lack of approval of the projects at Agenersa (Energy and Basic Sanitation Regulatory Agency). The concessionaire, however, guarantees that it will deliver the structure within the agreed deadline.

Oxygen injection is the newest technology to help with this goal. It consists of capturing part of the river flow, to process it with oxygen in tanks and return the water to the bed.

“What kills the river is the biological demand for oxygen. There is such a large organic load that all the biota dissolved there consumes all the oxygen available in the water and the river becomes dead. That strong smell comes because, in the absence of oxygen, the anaerobic bacteria generate methane”, says Sinval Andrade, the company’s institutional director.

“When you add oxygen, those anaerobic bacteria stop being the most populated, and those that live on oxygen start to become popular and consume organic matter.”

Águas do Rio’s oxygen tanks are installed in a corner of the old Célio de Barros athletics stadium, next to the Maracanã stadium. The Joana River passes in front of the sports complex.

The tests verify the water purification capacity over a kilometer. The objective is to evaluate the technology and the costs of its use.

The Joana River flows into the Mangue channel, which ends in the bay. In São Paulo, however, the technology was used on the Pinheiros River itself.

According to Cristina Zuffo, superintendent of research, development and innovation, the oxygen injection served as a “final barrier” to pollution in the water body.

“The Pinheiros River has several peculiarities. It doesn’t have a very high speed, it’s shallower, which also required an increase in oxygen in the river itself so that we could improve the quality even further”, she says.

The injection takes place close to the São Paulo pumping plant, the deepest point of the river. The technology is North American and was used for the first time in Brazil in the Novo Rio Pinheiros project.

The recovery units, in turn, have already been used in the past by the City of São Paulo in small streams in the capital, according to Nivaldo Rodrigues da Costa Junior, superintendent of Operational Engineering.

They basically divert part of the river’s course into a treatment plant, which returns cleaner water. These units served 5 of the 25 streams that flow into the Pinheiros River. They were only installed in places where expanding exclusive sewage collection or installing dry weather collectors were not feasible.

“They were part of the project’s composition. The main focus is, in addition to bringing about the universalization of sanitation, to bring environmental benefits and depollution of the river. The recovery unit is not a sewage or water treatment plant. It is something specifically to recover the river”, he explains.

In Rio de Janeiro, the strategy is tested on the Pavuna River, on the border with Duque de Caxias, which flows directly into the bay.

“These are all complementary strategies. In the past, we thought that sanitation was doing work. Sanitation is an exercise in operating. The work is a setback that we have to live through. That momentary inconvenience to provide that service”, says Andrade.

Zuffo emphasizes that “one technology alone is not miraculous” and states that the basis of the Pinheiros River project was to expand the sewage collection network to 650,000 homes and businesses, serving 1.8 million people. In Rio de Janeiro, the goal is to expand the service to 90% of the population by 2033, in line with the sector’s new regulatory framework.

“A series of actions are needed to achieve the final result. Infrastructure works, expansion of sewage treatment plants, recovery units [de rios] when it is not possible to enter communities, and new technologies, such as oxygen injection, to make a final polish of any remnants that are left, to guarantee a good water body”, she says.

The Guanabara Bay clean-up projects span over 40 years. After the concession of sanitation services, in 2021, the state government changed the strategy to achieve the objective

Instead of seeking to build an exclusive network to collect sewage from homes and businesses, it was decided to set up structures that prevent waste from being dumped into the riverbed through rainwater sewers. The strategy only works on dry days, which gives rise to its name (dry weather collectors).

The concessionaire states that it will complete the works on time. However, in a document sent to Agenersa, it predicted a two-year delay in completing the interventions.