A circular tale of water in three cities

View of city of Dakar, Senegal. Image: Sarah Farhat / The World Bank

A growing number of cities are adopting much more sustainable water and wastewater practices that create a valuable cycle of using and reusing resources.

Such practices are the building blocks of a circular economy, in which water, energy and other resources are managed sustainably and waste and pollution are reduced. All these efforts help preserve the environment and can generate revenue and cost savings.

With climate change already exacerbating water issues in cities, a new initiative at the World Bank Water Global Practice is supporting countries in adopting circular economy practices and building water resilience. Here are examples from three cities across three continents - Dakar, Guayaquil in Ecuador, and Chennai, India.

In Dakar, the capital of Senegal, which has a population of over 1 million, wastewater and sanitation byproducts are being turned into new resources by the city's utility. The Office National de l’Assainissement du Sénégal (ONAS) is piloting strategies to deal with shortfalls in water supply affecting customers and the region’s horticulturalists and farmers.

“In addition to being a precious raw material, purified water is a real alternative resource to water pressure and is a boon for the revival of agricultural development, public works, watering of green spaces."

Ababacar Mbaye, ONAS

The utility began to sell treated wastewater to local farmers, and later extended the system to irrigate the crops of hundreds of market gardeners near its Cambérène wastewater treatment plant. The facility is planning a massive increase in capacity from 19,000 to 92,000 m3 of wastewater per day.

"The various forms of recovery of the treated water from the treatment process of the Cambérène wastewater treatment plant which we have so far experimented with have finally proved to us the inestimable value of this by-product,” said ONAS managing director Ababacar Mbaye. “Indeed, in addition to being a precious raw material, purified water is a real alternative resource to water pressure and is a boon for the revival of agricultural development, public works, watering of green spaces, among others."

Women collect water in the Saint Louis region of Senegal - the country has big challenges on water. Image: Vincent Tremeau / The World Bank

Running on gas

To promote efficiency and reduce operational costs, the Cambérène wastewater plant also began recovering the biogas generated in the wastewater treatment process. It is now used to power the facility, resulting in a 28% saving in energy use.

The utility is also selling dried and stabilised fecal sludge as fertiliser to farmers and flower growers. It is processed by the wastewater treatment plant, which is run alongside a sludge treatment plant owned and operated by a private contractor.

The proximity and collaboration between the two plants ensures they can have economies of scale and are also close to the places where their products can be reused efficiently. Such forward thinking will be critical in the years ahead as Senegal innovates to address its water challenges, and Dakar is already a showcase for visitors from other countries.

River clean up

Sanitation is also front of mind in Guayaquil, Ecuador's main port, which has a population of some 3 million. The city is tackling a decades-long sewage pollution problem in its rivers and estuaries by focusing on improving sewerage infrastructure and ensuring even the poorest people have coverage and that customers can effectively connect to the network.

Water quality is monitored upstream of the city, and river basin planning is used to better understand water quality stressors. Two new plants will treat wastewater and again, transform biogas from sewage sludge digestion into enough electricity to meet 35-40% of the plants’ needs.

Chennai, on the Bay of Bengal in eastern India, came to global attention in 2019 when it ran dry of water. The city, which already has 11.5 million people, has responded to the need for more water, amid rapid industrial and population growth, by becoming more circular with its resources to build resilience.

Harvesting rainwater

The authorities mandated rainwater harvesting and Chennai became the first city in India to reuse 10% of collected wastewater, and has plans to achieve a reuse rate of 75 per cent. As part of this effort, the Chennai Metropolitan Water Supply & Sewerage Board (CMWSSB) sells treated wastewater to industrial users and with the additional revenues, it can cover all operating and maintenance costs.

CMWSSB is the only utility in India with two large-scale desalination plants. Energy is also recovered from wastewater in more than half of its wastewater treatment plants and the utility is preparing to sell most of the biosolids created by the process as manure for agricultural land.