Water

New study maps how much energy, nutrients and water are locked in world’s wastewater

Efficiently treating wastewater can help meet SDGs: UN-backed research

 
By Pushp Bajaj
Last Updated: Wednesday 05 February 2020
Wastewater. Photo: Mita Aggarwal / Down To Earth

The world generates about 380 trillion litres (tl) wastewater every year. This stores vast amounts of energy, nutrients for fertilisers besides, of course, water, according to recent study by the United Nations Institute for Water Environment and Health (UNU-INWEH).

In principle, nutrients such as nitrogen, phosphorous and potassium recovered from wastewater produced annually can offset 13.4 per cent of global demand to produce fertilisers.

Energy recovered from such wastewater — in the form of methane — can generate electricity for up to 158 million households. That’s roughly the current demand in the United States and Mexico combined.

Usable water reclaimed from wastewater can irrigate up to 31 million hectares (mha) of land, the study claimed.

The volume of wastewater being generated is projected to rise roughly 24 per cent by 2030 to 470 tl and 51 per cent by 2050 to 574 tl.

Treating wastewater efficiently can go a long way in achieving the UN-mandated sustainable development goals (SDG).

“Wastewater resource recovery will need to overcome a range of constraints to achieve a high rate of return. But success will significantly advance progress against SDGs and others, including adaptation to climate change, ‘net-zero’ energy processes, and a green, circular economy,” Manzoor Qadir, lead author of the study and assistant director at UNU-INWEH in Canada, said.

Researchers collected and analysed municipal wastewater data from a variety of sources at the national level in a given year. The data were then grouped together at regional and global scales.  

The study claimed that global wastewater generation roughly equalled the annual discharge from the Ganga. Asia contributed the most at 42 per cent, followed by Europe and North America (18 per cent each) in 2015.

Per capita, however, rich countries in North America generated almost 140 per cent more than the world average. Europe’s per capita output was half of North America’s. ‘Middle East and North Africa’ also exceeded the average. Asia placed fifth.

Previous studies have shown that wastewater contained nearly five times the energy needed to treat them. The primary source of that: Organic matter that can be converted into methane-rich biogas.

Assuming full-energy recovery, the new study estimated, current wastewater volume could provide enough methane fuel to power 196 million households by 2030 and 239 million households by 2050. 

In agriculture, treated wastewater can act as a much needed substitute to freshwater for irrigation. Water that can be potentially recovered can irrigate up to 31 mha — almost a fifth of farmland European Union has, the study estimated. 

Additionally, an estimated 16.6 Tg nitrogen, 3 Tg phosphorous and 6.3 Tg potassium were locked in global wastewater. The highly valuable nutrients are primarily used to produce fertilisers.

“The recovery of these nutrients from wastewater could result in a revenue generation of $13.6 billion globally,” the study noted. 

“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,” said Vladimir Smakhtin, Director of UNU-INWEH, in a press release. 

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