Wastewater: the untapped resource
What if we were to consider the vast quantities of domestic, agricultural and industrial wastewater discharged into the environment every day as a valuable resource rather than a costly problem? This is the paradigm shift advocated in the United Nations World Water Development Report ‘Wastewater: the untapped resource’, launched last week on World Water Day.
The report argues that, once treated, wastewater could prove invaluable in meeting the growing demand for fresh water and other raw materials. As noted by Guy Ryder, chair of UN-Water and director-general of the International Labour Organization, “Wastewater is a valuable resource in a world where water is finite and demand is growing.”
A large proportion of wastewater is still released into the environment without being either collected or treated — particularly in low-income countries, which on average only treat 8% of domestic and industrial wastewater, compared to 70% in high-income countries. As a result, water contaminated by bacteria, nitrates, phosphates and solvents is discharged into rivers and lakes ending up in the oceans, with negative consequences for the environment and public health.
Most governments and decision-makers have been primarily concerned by the challenges of water supply while overlooking the need to manage water after it has been used, yet the report states that these two issues are intrinsically related. The collection, treatment and safe use of wastewater are at the very foundation of a circular economy, the report finds, finding reclaimed water to be a largely underexploited resource which can be re-used many times.
At least 50 countries worldwide are known to use wastewater for agricultural irrigation, accounting for an estimated 10% of all irrigated land. But this practice raises health concerns when the water contains pathogens that can contaminate crops. The challenge, then, is to move from informal irrigation towards planned and safe use, as Jordan, where 90% of treated wastewater is used for irrigation, has been doing since 1977.
Treated wastewater can also serve to augment drinking water supplies, as is practised in Windhoek (the capital of Namibia), Singapore and San Diego. This practice can meet with resistance from the public, however, who may be uncomfortable with the idea of drinking or using water they consider to have once been dirty. Awareness-raising campaigns could help gain public acceptance for this type of practice by referring to successful examples, such as that of the astronauts on the International Space Station who have been re-using the same recycled water for over 16 years.
Wastewater can also be seen as a potential source of raw materials: certain nutrients, like phosphorus and nitrates, can now be recovered from sewage and sludge and turned into fertiliser. An estimated 22% of global demand for phosphorus, a finite and depleting mineral resource, could be met by treating human urine and excrement. Some countries, like Switzerland, have already passed legislation calling for the mandatory recovery of certain nutrients such as phosphorus.
The organic substances contained in wastewater could be used to produce biogas, which could help power wastewater treatment facilities, helping them transition from major consumers to becoming energy neutral or even net energy producers. In Japan, the government has set itself the target of recovering 30% of the biomass energy in wastewater by 2020. Every year, the city of Osaka produces 6500 tonnes of biosolid fuels from 43,000 tonnes of sewage sludge.
“The 2017 World Water Development Report shows that improved wastewater management is as much about reducing pollution at the source, as removing contaminants from wastewater flows, reusing reclaimed water and recovering useful by-products,” wrote UNESCO Director-General Irina Bokova in her foreword to the report.
“Raising social acceptance of the use of wastewater is essential to moving forward.”
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