Wastewater could power the US and Mexico

Total waste water production is set to increase by 24% over the 10 years, but a new study by the UN Institute for Water says we should regard wastewater as an untapped resource.

Those are the conclusions of a team led by Manzoor Qadir, who have estimated the world's total wastewater production. This is the first comprehensive study that includes places with little recorded data. According to its result, the total amount of wastewater produced per year globally could cover the Earth's entire land area (minus Antarctica) to a depth of 1 metre.

More importantly, they found that the energy stored in this water could power the equivalent of every single household in the US and Mexico, and replace 13% of fertiliser requirements.

As our global population is growing from 7.5 billion this year to 11 billion by 2050, demand for energy, food, and water will surge to supply the global population. Using wastewater as a source of energy and fertiliser could be one solution, says Qadir.

While a lot of wastewater treatment plants in Europe already produce energy from their wastewater, vast amounts of wastewater still go uncollected in large parts of the world.

This new global study shows the potential of wastewater to help nations augment their energy supplies and nutrient recovery from something that - at the moment - literally goes down the drain.

Energy can be produced by breaking down organic matter, after it is separated from the wastewater. Rich in nutrients and chemical energy, the bonds between the organic matter can be broken down in low oxygen environments. This process releases methane, a biogas which can be used to produce heat energy.

Furthermore, through the cycle of food from farm to plate, lots of nutrients end up in wastewater. The study found that the weight of nutrients present in wastewater amounts to 25.9 teragrams. This is 78 times the mass of the Empire State Building.

The nutrients found in wastewater are mainly nitrogen, potassium and phosphorus. These are the main components of fertiliser, and the main nutrients we need to eat.

These nutrients could be captured through nutrient recovery systems, and provide much needed fertiliser for our crops.  However these systems are currently very expensive, and it is difficult to extract all the desired nutrients at the same time.

This global wastewater study also found some large regional inequalities. Despite completely different population sizes, Africa, North America and Europe all produced about 67 billion cubic metres.

Indeed, North Americans produce 5 times more wastewater than people in African countries. This is caused, in part, by lower access to water in Sub-Saharan Africa, and also by lack of wastewater collection facilities.

To fund wastewater treatment plants, one approach taken in lower income countries, such as Jordan, has been to use a public-private partnership model. Traditionally municipalities have to carry the cost of water treatment, but this model enables private companies to fund and raise payments for the water treatment.

There are also major differences within the “developed world”: wastewater production per capita in Europe was half that of North America. Tariffs and tighter water quality standards have pushed European countries to develop a more resource conscious water infrastructure network.

This amount of wastewater produced annually is expected to increase by 24% within the next 10 years. Despite the high cost of treatment, resource recovery is essential to minimise future health and environmental impacts.