Water management is a problem but not a top priority in many of Brazil’s major cities. Typically, there are more pressing problems to be solved, and budgets are notoriously limited. For these and other reasons, the authors are using a low-tech approach that can be implemented quickly and easily for their Água Carioca project.

With a population of around 6.5 million, Rio de Janeiro is the second largest city in Brazil after São Paulo. As in many metropolises in South America, urban development has failed to keep up with population growth. On the city’s mountainsides especially, informal settlements have arisen, and these are growing denser and more populous. In Rocinha alone, which is probably the largest favela in South America, an estimated 200,000 people live shoulder to shoulder under hazardous sanitary conditions. Most of the city’s wastewater – 18,000 liters per second – is flushed into Guanabara Bay as raw sewage.

Engineer Eva Pfannes (pictured, left) studied at the Stuttgart State Academy for Art and Design and at the Bartlett School of Architecture in London. Born in Ingolstadt, Germany, she has worked in the offices of Maxwan in Rotterdam, Zaha Hadid in London, and Studio Makkink & Bey in Rotterdam. In 2003 she founded Ooze Architects with Sylvain Hartenberg in Rotterdam, the Netherlands. Sylvain Hartenberg (pictured, right), born in Paris, studied in Strasbourg at the Institut national des sciences appliquées de Strasbourg and in London at the Bartlett School of Architecture. The architect worked in Paris for Architecture Studio and in London for Terry Farell and Sheppard Robson. Eva Pfannes and Sylvain Hartenberg are not only business partners but a couple in private life.

Governments set priorities, and that’s no different in Rio de Janeiro. But because water quality doesn’t directly affect productivity, as do for example poor roads or power outages, other projects are often given priority. Making matters worse, the favelas of the megacity are at best only semi-institutionalized. Roles and responsibilities are not clearly defined so it ’s always easy for officials to pass the buck. Thus, the first task of the project team was to visit all the key officials and star t convincing them of their plans. In doing so, another hurdle for the realization of the project soon became evident. Although city administrators were interested in implementing a water-treatment project, it was quickly made clear that the city lacked the necessary funds.

Currently, wastewater from Rio’s favelas is dumped into the ocean via a network of pipelines, open channels, and sometimes via makeshift ditches – a foul-smelling, environmentally detrimental, and unhealthy situation. Wastewater management in Rio de Janeiro is failing mainly due to two big problems: First, although there is a water treatment plant outside the city, it’s only operating at partial capacity. Because the sewer network is incomplete, only about ten percent of the wastewater is sent there and treated. And second, the infrastructure installed during the urbanization in the 1960s and 1970s fails to meet today’s requirements, and political and financial difficulties have prevented further improvement.

The approach of Água Carioca is persuasively simple: If the big solution fails, switch to many small solutions. For instance, groups of 10 to 15 houses share a constructed wetland. Each house has its own cistern and septic tank. Rainwater is collected in the cistern, and sewage is collected in the septic tank. It is pre-treated before being fed into the open, constructed wetland along with the rainwater. There, plants and microorganisms provide further purification of the water until it is clean enough to be reused for toilet flushing, washing, and irrigation. The full cycle takes about a week, and 90 percent of the water can be reused at the end. The other 10 percent is lost through evaporation. As sediment accumulates in the septic tanks; it must be cleaned out every two years.

As part of their project, the architects developed design proposals to show that the low-tech principle, which is comparable to that of natural swimming pools, works at both the smallest and the largest scales. At the smallest scale, a modified Água Carioca could provide wastewater treatment for a school – and serve as an example of sustainability there as well. At the midsize scale, based on a system for the favela Morro da Formiga with its approximately 4,500 inhabitants, it was shown that the constructed wetlands can provide public green spaces in addition to wastewater treatment. In the end, the principle of the project could even help relieve the heavily polluted Guanabara Bay, gateway to the city of millions.

Read the full article: “Utopias can become reality” in Fifth LafargeHolcim Awards – Sustainable Construction 2017/2018