Countries that recycle wastewater into drinking water

Julie Mendret, August 2023

The Conversation

While the idea may still make many people grimace, it is nevertheless becoming a serious option for more and more countries and municipalities around the world that are rightly concerned about dwindling freshwater resources. The megacity of Bangalore in India is working on such a wastewater recycling system, as is Los Angeles.

In the United States, the Texan cities of Big Springs and Wichita Falls have already been using this technique, known as direct potable reuse, since 2011, as has the city of Beaufort in South Africa.

Namibia has been treating wastewater for drinking water since 1968

However, in this area, and this remains little known, another country remains the undisputed pioneer: Namibia. Ranked 139th in the list of countries by level of development, it may seem surprising that this southern African country is so far ahead, but when you consider the virtual absence of water resources in its capital, Windhoek, it is 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 (population nearly 500,000) cannot harvest the scarce rainwater, which evaporates almost immediately in its desert climate, nor can it draw on rivers or groundwater in the surrounding area, which are rarely replenished when they are not completely dry.

In 1968, the city, then under South African rule, was experiencing impressive population growth when it began recycling its wastewater to produce drinking water. Fifty-five years later, 30% of wastewater is recycled into drinking water in less than ten hours. The rest of the domestic drinking water comes from dams and boreholes in other parts of the country.

Wastewater purified in 10 steps

In order to recycle wastewater into drinking water, Windhoek has implemented a series of innovative processes that now consists of 10 steps. It includes physical and chemical processes, such as coagulation and flocculation (adding a coagulant to create flocs, i.e. clusters of suspended matter that then sink due to their weight and are eliminated in the sludge), as well as chemical processes such as ozonation.

When it comes into contact with ozone, the water undergoes an oxidation process that breaks down many micropollutants (pesticides, drug residues, etc.) and inactivates bacteria, viruses and parasites.

This is followed by final stages of biological filtration using granular activated carbon and physical filtration (activated carbon filtration and membrane ultrafiltration) to remove any remaining soluble pollutants. Before being sent to the network, the water undergoes quality controls and chlorination, ensuring a long-lasting disinfecting effect so that the quality of the water obtained does not deteriorate during distribution.

In recent years, the Windhoek wastewater treatment plant has welcomed intrigued and interested visitors from Australia, Germany, the United Arab Emirates and elsewhere. And with good reason, as the techniques developed in Namibia remain interesting for a number of reasons.

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 widespread throughout the world. While wastewater treatment consumes between 1 and 1.5 kWh per m3, desalination requires between 3 and 4 kWh per m3. In addition, the latter technique produces bulky waste: salt and pollutant concentrates that are often discharged directly into the seas and oceans, where they disrupt ecosystems.

Despite all these advantages and the convincing results in Namibia, wastewater treatment is still in its infancy on a global scale because its implementation involves overcoming various barriers. Firstly, there is the cost of installation. Currently, only developed countries have been able to finance such projects, either on their own soil (in the United States, Singapore, etc.) or abroad, with, for example, the modernisation of the Namibian plant being backed by a public-private partnership between the French company Veolia, the Australian-Indian company Wabag and the city of Berlin.

Financial, legislative and psychological obstacles

Secondly, because the legislation in different countries remains very restrictive. In Europe, for example, such a plant would not currently be authorised, and the only project underway to treat wastewater for drinking purposes, the Jourdain Programme in the Vendée region, will discharge the water into a reservoir used as a reserve for drinking water production rather than directly into the water distribution system: this is known as indirect potabilisation.

And even when the funds and laws are in place to allow the direct use of drinking water from treated wastewater, one final barrier remains, and it is not the least of them: making it acceptable to the population to drink treated wastewater, and overcoming what is known as the ‘yuck factor’. In 2000, a $55 million wastewater treatment plant in a Los Angeles neighbourhood had to close a few days after opening because ‘never drink toilet water’ had become an election promise of the politician running for mayor.

In Namibia, this problem did not arise when wastewater treatment was introduced because the inhabitants of Windhoek, then under apartheid, were presented with a fait accompli three months after the first plant became operational. However, in an article in the Sunday Tribune in November 1968, the journalist covering the announcement of this new wastewater recycling system reported 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, not informing the population in advance remains a radical and unadvisable solution, as raising public awareness of water scarcity and the need for more sustainable alternatives is still the best way to launch such a project. This is what made the Singapore project a success, as it focused heavily on communication about the treated wastewater purification project, for example by organising visits to the treatment plant and showing the then Prime Minister drinking a glass of the new recycled wastewater.

As a result, the yuck factor was transformed into national pride. Pride in mastering cutting-edge technology and pride in gaining greater independence from neighbouring Malaysia, which remained its main supplier of drinking water and with which diplomatic relations could be tense.

Beware of the ‘rebound effect’

But in its quest for water self-sufficiency, Singapore has not put all its eggs in one basket, and has also invested in seawater desalination, rainwater harvesting and reducing its residents’ water consumption (from 165 litres per capita per day in 2000 to 141 litres in 2018).

For all advocates of better water resource use, this restraint is crucial, both upstream and in parallel with the development of wastewater treatment projects, in order to combat what is now known as the ‘rebound effect’. This expression describes the uninhibited and increasing use of water resources following the introduction of desalination or treated wastewater reuse techniques. These new water resources should only be considered 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.

In order to maximise the resources at our disposal, the wastewater recycling plants of the future will also have to recover the waste produced by wastewater treatment processes, for example by transforming phosphorus and nitrogen into nutrients useful for agriculture, or by producing energy through methanisation using the waste collected during treatment as input.

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