Wastewater reuse: a solution with a future (2023)

1“In Windhoek, every drop of water counts” is the motto of the Namibian capital. Namibia is one of the world’s most arid countries, traversed by the Kalahari and Namib deserts and bordered by the Atlantic Ocean to the west. In Namibia, heat causes 83% of rainwater to evaporate, with just 1% absorbed into the ground. With chronic water stress and no nearby water courses, in 1968 the city decided to recycle wastewater for reintroduction into its water supply network, making it the first city in the world to reuse domestic wastewater for human consumption.

2The policy provided an additional water source for over 20 years, but was soon under pressure from Windhoek’s rapid population growth following independence in 1990. In 2002, a new treatment plant was built and handed over to Veolia to operate. With a daily capacity of 21,000 cubic meters, the plant currently supplies over a third of the city’s drinking water in the form of tap water used by almost 400,000 residents.

3Windhoek’s water treatment plant uses cutting-edge technologies that mimic nature to eliminate all possible health hazards. Domestic effluents are first treated in the City wastewater treatment plant (WWTP) using an activated sludge process and maturation ponds. They then pass into the DPR (Direct Potable Reuse) plant where several treatment steps mimic the natural water cycle and ensure a water quality that meets the world’s highest standards. A number of innovative technologies have been deployed, including biological filtration and granular activated carbon filtration. Critically, the multiple barrier technique reproduces the natural water cycle in several phases: pre-ozonation, coagulation/flocculation, floatation, sand filtration, ozonation, filtration, activated carbon adsorption, ultrafiltration and chlorination. These different phases have the advantage of eliminating a number of the primary elements in wastewater, such as physical and organoleptic elements, macro-elements, and microbiological and disinfectant by-products.

4The resulting potable water is subject to permanent quality controls. This is key to the safety of water sources as well as to public trust. All routine testing – physical, inorganic and organic chemistry, microbiology and viral indicators – is carried out in the city’s analysis laboratory. There is also a program for managing health risks that feeds into a number of research projects. These encompass advanced testing for virology, parasites, toxicity, pesticides, algae toxins, etc., carried out by third-party laboratories. And as the plant is fully automated, an online sampling system is located in each primary treatment unit to provide continuous inspection of turbidity, pH, conductivity, dissolved oxygen, chlorine, etc.

5In total, it takes around 10 hours from the moment wastewater arrives at the treatment plant to the moment it leaves as drinking water. This high-quality recycled water resulted in the installation of new water distribution points in townships, helping to improve the health and safety of residents.

6The Windhoek treatment plant has become a global benchmark and a model for innovative and sustainable water management. It is also an example of a successful public-private partnership that is increasingly visited by officials from across Africa as well as numerous experts from Australia, Singapore and the USA.

7The Windhoek case is the longest-running and most emblematic project for the direct reuse of treated wastewater for the production of drinking water for human consumption. But direct reuse of wastewater without a passage via the natural environment remains extremely rare. Worldwide, only 4% of wastewater is recycled. And it is a resource most commonly destined for uses other than tap water.

8The full potential of wastewater remains very much under-exploited. But this is a “new black gold” according to a 2017 UN report on wastewater released to coincide with World Water Day. The report’s authors suggested that we should think of wastewater as a resource. Reuse is an inescapable solution if we are to limit the ballooning demand for water caused, in every corner of the planet, by population growth, better living conditions in developing economies, urban growth and the demands of agriculture.

9Water is a resource under pressure and, although the first response is to optimize consumption, reusing recycled wastewater is a way to protect this resource. Take agriculture as an example. The use of recycled wastewater for irrigation represents 32% of the global market, but this use could become far more systematic. Wastewater is rich in nitrogen and phosphorus so it can provide nutrients to crops. The critical challenge for agricultural irrigation is to preserve a portion of the nitrogen and phosphorus contained in the wastewater, because these are valuable nutrients for plants. This also avoids using fertilizers that are energy- and resource-intensive to manufacture, particularly with phosphorus potentially in short supply by2050.

10Providing access to water to the majority of people while also protecting the environment is a twofold objective that wastewater reuse delivers – it is a solution with a future.

11After irrigation for agriculture, reuse is primarily focused on watering green spaces (20%) and in manufacturing (19%). To recycle water is to boost its productiveness. This is a key issue for manufacturers when you consider that it takes 400,000 liters of water to make a car, 11,000 liters to make a pair of jeans and 1,300 liters for a cellphone. This is what we are doing in Durban, South Africa, where we recycle 98% of the wastewater from the city’s Southern Wastewater Treatment Works (SWTW) for reuse by manufacturers in their production processes.

12Veolia put this virtuous solution for adapting to the climate emergency in place as part of South Africa’s first ever public-private partnership.

13Recycling water for industrial applications means less water has to be taken from the natural environment and freshwater resources can be reserved for the production of drinking water. The plant can indeed provide an additional capacity of 47,000 cubic meters of drinking water each day, equivalent to 13 Olympic-size swimming pools.

14And as water can account for as much as 15% of industrial costs (process water, hot water, air conditioning, washing, etc.), the reuse of recycled wastewater is a fantastic opportunity in terms of cost control: the Durban-based manufacturers partnering with the project save over €5 million a year.

15The time has come to think differently about the water we drink, the water that is used to irrigate fields, water parks and gardens or as part of industrial processes, before it is returned to nature.

16There is, however, no escaping the fact that this alternative solution will develop at different rates in different parts of the world, reflecting the specific requirements of each local regulatory environment. It also suffers from problems of social acceptability and, despite all the economic and environmental advantages, projects involving reuse of wastewater can be a source of concerns. Recycling equates to waste reuse and, no matter its potential, this is something that remains unacceptable for certain religious or cultural reasons. In all cases, these types of projects have to be backed by the full range of educational and awareness-raising measures that are vital to gaining the trust of all stakeholders concerned. Responding to community anxieties is absolutely critical.

17The Windhoek experience demonstrates that it is possible to boost a city’s drinking water supply by using recycled wastewater in a safe and responsible manner. However, operating wastewater retreatment plants requires exemplary professionalism and faultless reliability. These are preconditions for ensuring consumers’ health.

18Depending on uses and needs, wastewater treatment plants could provide water of a quality suited to every situation. Regulations permitting, we can provide high-quality drinking water in this way thanks to innovative treatment and surveillance technologies that guarantee the absence of any risk to human health.

19Under these conditions, are we ready to put our worries and taboos to one side and use recycled wastewater on a daily basis? It all depends on the planned uses, of course, but growing awareness of the environmental emergency and fears of water stress, coupled with technologies that are now mature, should mean that reuse cements its position as an effective solution for guaranteeing access to water in the years to come.

20This is a solution for the future in all parts of an African continent experiencing a population boom that, according to the UN, will mean that 75 to 250 million people will be living in regions grappling with major water stress by 2030.