Countries that recycle wastewater into drinking water
English speakers like to call this water “toilet-to-tap water.” Literally: water that goes from your toilet bowl to your faucet. It’s an unappealing term that overlooks the many chemical, physical, and biological processes involved in recycling wastewater into high-quality drinking water.
Julie Mendret, University of Montpellier
While this idea may still make many people cringe, it is nonetheless becoming a serious option for an increasing number of countries and municipalities around the world that are rightly concerned aboutthe dwindling supply of freshwater. The megacity of Bangalore, India, is exploring such wastewater recycling, as is Los Angeles.
In the United States, the Texas cities of Big Springs and Wichita Falls have already been using this technique, known as direct potable reuse, as has the city of Beaufort in South Africa since 2011.
Namibia has been treating wastewater since 1968
But in this regard—and this remains largely unknown—it is yet another country that stands as the undisputed pioneer: Namibia. Ranked139thin the list of countries by level of development, one might be surprised that this Southern African nation is so far ahead of the curve, but when one considers the near-total lack of water resources in its capital, Windhoek, it becomes immediately less surprising that this municipality has sought to innovate.
In the middle of an arid plain, more than 200 km from the coast, Windhoek (with a population of nearly 500,000) cannot harvest the scarce rainwater—which evaporates almost immediately at these desert latitudes—nor can it draw from the rivers or groundwater sources in the surrounding area, which replenish very little when they are not completely dry.
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In 1968, the city—then under South African rule—was also seeing its population grow at an impressive rate when it began recycling its wastewater to turn it into drinking water. Fifty-five years later, 30% of the wastewater is recycled into drinking water in less than ten hours. The rest of the domestic drinking water comes from dams and wells in other parts of the country. https://www.youtube.com/embed/arCmp7jOjiw?wmode=transparent&start=0
Treating wastewater into drinking water in 10 steps
To enable the recycling of wastewater into drinking water, Windhoek has implemented a series of innovative processes that now consists of 10 steps. It includes physicochemical processes, such as coagulation and flocculation (the addition of a coagulant to form flocs—clusters of suspended matter that then settle due to their weight and are removed in the sludge), as well as chemical processes such as ozonation.
When exposed to ozone, the water undergoes an oxidation process that breaks down many micropollutants (such as pesticides and drug residues) and inactivates bacteria, viruses, and parasites.
Next come the final stages of biological filtration using granular activated carbon and physical filtration (activated carbon filtration and membrane ultrafiltration), which remove any remaining soluble contaminants. Before being released into the distribution network, the water undergoes quality checks and chlorination, ensuring a long-lasting disinfecting effect so that the quality of the treated water does not deteriorate during distribution.
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In recent years, the Windhoek wastewater treatment plant has welcomed curious and interested visitors fromAustralia, Germany, the United Arab Emirates, and elsewhere. And for good reason: the technologies developed in Namibia are noteworthy in more ways than one.
A less expensive solution than desalination
For countries seeking new sources of drinking water, wastewater recycling remains less energy-intensive and more environmentally friendly than seawater desalination, a technique that is nevertheless more widely used around the world. While treating wastewater to make it safe for drinking consumes between 1 and 1.5 kWh percubic meter, desalination requires between 3 and 4 kWh percubic meter. Furthermore, desalination produces bulky waste: concentrates of salts and pollutants that are often discharged directly into the seas and oceans, where they disrupt ecosystems.
Despite all these advantages and the compelling results from the Namibian case, wastewater reclamation is still in its infancy on a global scale because its implementation requires overcoming various barriers. First and foremost is the cost of installation. Currently, only developed countries have been able to finance such projects, either domestically (in the United States, Singapore, etc.) or abroad. For example, the modernization of the Namibian plant was backed by a public-private partnership involving the French company Veolia, the Australian-Indian firm Wabag, and the city of Berlin.
Financial, legislative, and psychological barriers
Furthermore, because the laws in different countries remain very restrictive. Thus, in Europe, such a plant would not currently be authorized, and the only ongoing project to make treated wastewater potable—the Jourdain Program in the Vendée region—will discharge the water into a reservoir used as a source for drinking water production, rather than directly into the water distribution system: this is known as indirect potabilization.
And even when the funding and legislation are in place to allow the direct use of treated wastewater as drinking water, one final—and by no means minor—barrier remains: convincing the public that it is acceptable to drink treated wastewater, and thereby overcoming what is known as the “yuck factor.” In 2000, a wastewater treatment plant in a Los Angeles neighborhood, which had cost $55 million to build, had to close just a few days after opening because “never make people drink toilet water” had become an election promise of the politician running for mayor.
In Namibia, this issue did not arise when wastewater treatment was introduced because the residents of Windhoek, then under apartheid rule, were presented with a fait accompli three months after the first plant began operations. In a November 1968 article in the Sunday Tribune, however, the reporter covering the announcement of this new wastewater recycling initiative noted that the mayor of Windhoek at the time, in a blind taste test, preferred the taste of treated wastewater to that of water from conventional sources.
The example of Singapore
However, failing to inform the public in advance remains a radical and ill-advised approach, as raising public awareness about the scarcity of water resources and the need for more sustainable alternatives remains the best way to launch such a project. This is what made the Singapore project a success; the city invested heavily in communication surrounding the treated wastewater reclamation project, for example by organizing tours of the treatment plant or by showing the prime minister at the time calmly drinking a glass of this new recycled wastewater.
And so the “yuck” factor turned into a source of national pride—pride in mastering cutting-edge technology and pride in gaining greater independence from neighboring Malaysia, which remained its main supplier of drinking water and with which diplomatic relations could be strained.
Watch out for the “rebound effect”
But in an effort to achieve self-sufficiency in water resources, Singapore has not put all its eggs in one basket; it has also invested in seawater desalination, rainwater harvesting, and reducing its residents’ water consumption (which fell from 165 liters per person per day in 2000 to 141 liters in 2018).
For all advocates of more efficient water use, this restraint is essential—both prior to and alongside the development of wastewater treatment projects—in order to combat what is now known as the “rebound effect.” This term describes the unchecked and increasing use of water resources following the implementation of desalination or treated wastewater reuse technologies. These new water resources should, in fact, be viewed solely as a means of meeting existing and essential needs and uses—often as a substitute for drinking water—and not as a call to create new ones.
To make the most of the resources at our disposal, wastewater treatment plants of the future will also need to recover the waste generated by wastewater treatment processes—for example, by converting phosphorus and nitrogen into nutrients useful for agriculture, or by generating energy through anaerobic digestion using the waste collected during treatment as feedstock.
This article is part of a project in collaboration between The Conversation France and AFP Audio. It received financial support from the European Journalism Centre as part of the “Solutions Journalism Accelerator” program, supported by the Bill & Melinda Gates Foundation. AFP and The Conversation France maintained their editorial independence at every stage of the project.
Julie Mendret, Associate Professor, HDR, University of Montpellier
This article is republished from The Conversation under a Creative Commons license. Readthe original article.