资源环境科技发展态势分析平台

Canadian scientists have identified a new source of energy, wealth and nourishment being lost every day in every city, town and municipality on the planet: a great river of wastewater.

What swirls down the kitchen and bathroom plugholes in every home, cascades into the town drains and flushes the city sewers contains enough latent energy to power almost 160 million households.

The flow of wasted water is big enough to irrigate up to an area equal to one-fifth of all the farmland in the European Union. And the nitrogen, phosphorus and potassium that sluices down the world’s drains would be enough to meet almost one-eighth of the world’s fertiliser demand, and notionally generate a revenue stream of more than $13 bn a year.

In effect, the researchers argue, humans are every day flushing good money down the toilet. And this stream of lost income could only keep growing. Right now, according to a new study in the UN journal Natural Resources Forum, the world’s wastewater discharges add up to 380 billion cubic metres a year.

This is five times the volume of the water tumbling over Niagara Falls on the US-Canadian border. It is equivalent to the entire flow of the Ganges through the Indian subcontinent: it could fill Africa’s Lake Victoria in seven years, and Switzerland’s Lake Geneva in three months.

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Municipal wastewater was and often still is seen as filth.

Vladimir Smakhtin, director, UN University institute

Research of this kind has two functions. One of them is to underline the sheer scale of the destructive challenge of the Anthropocene, the new informal name for the geological epoch inaugurated in the last century by one species, Homo sapiens, at the expense of the other 10 million species on the planet. And the other is to highlight the potential squandered by people, industry and government every day, everywhere.

How much of all of this diluted wealth and power could be recovered and used again is not certain. What researchers based at the UN University Institute for Water, Environment and Health in Ontario have established is that such issues might repay investment, especially as the volume of wastewater is certain to grow: by almost a quarter in the next decade, and by more than 50 per cent by 2050.

“Municipal wastewater was and often still is seen as filth,” said Vladimir Smakhtin, who directs the UN University institute.

“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.”

The scientists worked from data produced by UN, European Union and other sources wherever they could find them to assemble a kind of inventory of the world’s wastewater, and what gets wasted with it.

Choking the oceans

Every year, the drains and sewers carry more than 16 million tonnes of dissolved nitrogen and 3m tonnes of phosphorus.

Four-fifths of the first element and half of the second are supplied by human urine, and the resource isn’t simply wasted: this global excess of nutrients goes on to nourish dangerous levels of plant growth and feed oxygen demand in the world’s waters, helping to stifle aquatic life.

The energy roaring down the drains in the form of the constituents of the natural gas methane could in theory generate enough electricity to fuel all the homes in the US and Mexico, and the volume of wastewater is enough to irrigate two harvests a year from a farmland area of more than 30 million hectares.

The continent of Asia already flushes away almost 160bn cubic metres a year. North America and Europe waste around 67bn cubic metres each, at a rate of – in the US – 231 cubic metres per person per year. Africa by contrast discards only 95 cubic metres per capita, because water supplies are all too often limited and wastewater is poorly managed in many African cities.

“Wastewater resource recovery will need to overcome a range of constraints to achieve a high rate of return,” said Manzoor Qadir of the UNU institute, who led the study “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.” 

This story was published with permission from Climate News Network.