Though most developed countries treat sewage, treatment levels do not generally remove nutrients from the wastewater that is discharged. One exception is the state of Maryland (U.S.) where all major sewage treatment plants are required to upgrade to enhanced nutrient removal technologies that will remove most of the nutrients from the wastewater.
Vast amounts of valuable energy, agricultural nutrients, and water could be recovered from the world’s fast-growing volume of municipal wastewater.
Some 380 billion cubic meters (1 m³ = 1000 litres) of wastewater are produced annually worldwide — five times the amount of water passing over Niagara Falls annually. That’s enough to fill Africa’s Lake Victoria in roughly seven years, Lake Ontario in four.
Furthermore, wastewater volumes are increasing quickly, with a projected rise of roughly 24% by 2030, 51% by 2050.
Looked at another way, the volume of wastewater roughly equals the annual discharge from the Ganges River in India. By the mid-2030s, it will roughly equal the annual volume flowing through the St. Lawrence River, which drains North America’s five Great Lakes.
Among major nutrients, 16.6 million metric tonnes of nitrogen are embedded in the world’s current annual volume of wastewater, together with 3 million metric tonnes of phosphorus and 6.3 million metric tonnes of potassium.
Theoretically, the recovery of these nutrients could offset 13.4% of global agricultural demand for them.
Recovery of these nutrients in that quantity could generate revenue of $13.6 billion globally at current prices: $9.0 billion in nitrogen, $2.3 billion in phosphorus, and $2.3 billion in potassium.
The energy embedded in wastewater, meanwhile, could provide electricity to 158 million households — roughly the number of households in the USA and Mexico combined.
Beyond the economic gains, environmental benefits of recovering these nutrients include minimizing eutrophication — the phenomenon of excess nutrients causing dense plant growth and aquatic animal deaths due to lack of oxygen.
In its new study, funded by the Government of Canada, the UN University Institute for Water, Environment and Health (UNU-INWEH) provide these estimates and projections based on a new analysis of the world’s total annual wastewater production.
In many countries, official data on wastewater is often scattered, poorly monitored and reported, or simply unavailable. Nonetheless, our study offers important approximations of global and regional wastewater volumes and insights into its potential benefits.
Our study found that Asia is the largest wastewater producing region by volume — an estimated 159 billion cubic meters, representing 42% of urban wastewater generated globally, with that proportion expected to rise to 44% by 2030.
Other top wastewater-producing regions: North America (67 billion cubic meters) and Europe (68 billion cubic meters) — virtually equal volumes despite Europe’s higher urban population (547 million vs. North America’s 295 million).
The difference is explained by per capita generation: Europeans 124 cubic meters; North Americans 231 cubic meters).
By contrast, Sub-Saharan Africa produces 46 cubic meters of wastewater per capita — about half the global average (95 cubic meters), reflecting limited water supply and poorly-managed wastewater collection systems in most urban settings.
Achieving a high rate of return on wastewater resource recovery will require overcoming a range of constraints. But success would significantly advance progress against the Sustainable Development Goals and others, including adaptation to climate change, ‘net-zero’ energy processes, and a green, circular economy.
It is important to note that many innovative technologies are available today and are being refined to narrow the gap between current and potential resource recovery levels. In the case of phosphorous, for example, recovery rates of up to 90% are already possible.
Also needed to advance progress: to leverage private capital by creating a supportive regulatory and financial environment, particularly in low- and middle-income countries where most municipal wastewater still goes into the environment untreated.
Municipal wastewater was and often still is simply deemed to be filth. However, attitudes are changing with the growing recognition of the enormous potential economic returns and other environmental benefits its proper management represents.
As the demands for freshwater grow and scarce water resources are increasingly stressed, ignoring the opportunity for greater use of safely-managed wastewater is an unthinkable waste.
We hope this study helps inspire the development of national action plans leading to wastewater collection and resource recovery and reuse.
Safely managed, wastewater is a key achieving the Sustainable Development Goals (SDGs), particularly SDG 6.3, which calls on the world to halve the proportion of untreated wastewater, and to substantially increase its recycling and safe reuse globally by 2030.
*The paper, “Global and regional potential of wastewater as water, nutrient, and energy source,” is published by Wiley in Natural Resources Forum, a UN Sustainable Development Journal. Co-authors: Manzoor Qadir, Praem Mehta, UNU-INWEH, Canada; Younggy Kim, McMaster University, Canada; Blanca Jiménez Cisneros, UNAM, Mexico; Pay Drechsel, IWMI, Sri Lanka; Amit Pramanik, Water Research Foundation, USA; Oluwabusola Olaniyan, Winnipeg Water and Waste Department, Canada.
Top photo credit: Chesapeake Bay Program/Flickr