Enough energy to power all households in the USA and Mexico; enough nutrients to meet ~13% of world fertilizer needs; enough water to fill Lake Victoria in seven years, Lake Ontario in four; UN University foresees 24% wastewater rise by 2030; 51% by 2050.
Vast amounts of valuable energy, agricultural nutrients, and water could potentially be recovered from the world’s fast-rising volume of municipal wastewater, according to a new study by UN University’s Canadian-based Institute for Water, Environment and Health (UNU-INWEH).
Today, some 380 billion cubic meters (m3 = 1000 liters) of wastewater are produced annually worldwide — 5 times the amount of water passing over Niagara Falls annually — enough to fill Africa’s Lake Victoria in roughly seven years, Lake Ontario in four, and Lake Geneva in less than three months.
Furthermore, the paper says, wastewater volumes are increasing quickly, with a projected rise of roughly 24% by 2030, 51% by 2050.
Today, 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 tons of nitrogen are embedded in wastewater produced worldwide annually, together with 3 million metric tons of phosphorus and 6.3 million metric tons of potassium. Theoretically, full recovery of these nutrients from wastewater could offset 13.4% of global agricultural demand for them.
Beyond the economic gains of recovering these nutrients are critical environmental benefits such as minimizing eutrophication — the phenomenon of excess nutrients in a body of water causing dense plant growth and aquatic animal deaths due to lack of oxygen.
The energy embedded in wastewater, meanwhile, could provide electricity to 158 million households — roughly the number of households in the USA and Mexico combined.
The study’s estimates and projections are based on theoretical amounts of water, nutrients, and energy that exist in the reported municipal wastewater produced worldwide annually.
The authors underline that information on wastewater volumes — generated, available, and reused — is scattered, infrequently monitored and reported, or unavailable in many countries. They also acknowledge the limitations of current resource recovery opportunities.
Nonetheless, says lead author Manzoor Qadir, Assistant Director of UNU-INWEH, in Hamilton, Canada: “This study offers important insights into the global and regional potential of wastewater as a source of water, nutrients, and energy. Wastewater resource recovery will need to overcome a range of constraints to achieve a high rate of return 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.”
The paper cites prior research showing that human urine is responsible for 80% of the nitrogen and 50% of phosphorus entering municipal wastewater treatment plants. “Removing these nutrients in time would not only be environmentally beneficial,” the paper says, “resulting in less eutrophication, it would reduce the cost of wastewater treatment while supporting closed-loop processes.”
Current wastewater nutrient recovery technologies have made significant progress. In the case of phosphorous, recovery rates range from 25% to 90%.
The paper points out that maximizing economically the potential use of thermal energy in wastewater swings on several basic requirements, including a minimum flow rate of 15 litres per second, short distances between heat source and sink, and high-performance heat pumps.
Says Vladimir Smakhtin, Director of UNU-INWEH, a global leader in research related to unconventional water sources: “Municipal wastewater was and often still is seen as filth. However, attitudes are changing with the growing recognition that enormous potential economic returns and other environmental benefits are available as we improve the recovery of the water, nutrients and energy from wastewater streams.”
“Safely managed wastewater is the key to water-related sustainable development at a time when the world is embarking on achieving SDGs, particularly SDG 6.3, which calls on us to half the proportion of untreated wastewater and substantially increase recycling and safe reuse globally by 2030.”
Praem Mehta, UNU-INWEH / McMaster University, Hamilton, Canada
“This data can be used to develop national action plans aiming at water resources management, pollution control measures, nutrient and fertilizer access, and energy recovery and energy production systems.”
Younggy Kim, McMaster University, Hamilton, Canada
“It is important to note that many innovations are available and are being refined to bridge the gap between current resource recovery levels and resource recovery potential.”
Blanca Jiménez Cisneros, UNESCO and the National Autonomous University of Mexico
“For countries to progress, there is a need to invest in a supportive regulatory and financial environment towards a green economy, and to leverage private capital for resource recovery-related business models that are financially feasible and increase cost recovery from municipal wastewater.”
Pay Drechsel, International Water Management Institute, Sri Lanka
“There is a need to facilitate and expedite implementation of resource recovery innovations particularly in low- and middle-income countries where most municipal wastewater still goes into the environment untreated. This concerns mainly the growing small and medium-size towns where agricultural land is still in proximity but also urban agricultural areas around larger cities.”
Amit Pramanik, Water Research Foundation, Alexandria, VA, USA
“The SDG challenge is on, and step-wise approaches are needed which should involve both the public and emerging private sectors which often struggle with inadequate regulatory frameworks, limited finance, and the lack of capacity to develop or evaluate bankable business plans about resource recovery and reuse. As the demands for freshwater are ever-growing and scarce water resources are increasingly stressed, ignoring the opportunities leading to safely managed wastewater is nothing less than unthinkable in the context of a circular economy.”
Oluwabusola Olaniyan, Winnipeg Water and Waste Department, Canada.
Reference: “Global and regional potential of wastewater as a water, nutrient and energy source” by Manzoor Qadir, Pay Drechsel, Blanca Jiménez Cisneros, Younggy Kim, Amit Pramanik, Praem Mehta and Oluwabusola Olaniyan, 27 January 2020, Natural Resources Forum.
DOI: DOI: 10.1111/1477-8947.12187
Funding: Global Affairs Canada / Government of Canada
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