Sewage could provide a novel way of helping consumers with soaring food bills and reducing pollution in our waterways – if sewage plants separated out phosphorus, a vital ingredient of fertiliser, according to a new report.
Phosphorus, found naturally in all plants, is essential for growing plants but its use as a fertiliser is creating widespread pollution in developed countries, because much of it is wasted. Phosphorus is a leading cause of water pollution, as the runoff from fertiliser use in fields produces an excess of nutrients that upset the natural balance of rivers and ponds, leading to algae blooms that harm fish and plants.
Most of the phosphorus used to make fertiliser is mined from rock, rather than recycled from sources such as sewage. Only about 15% of the phosphorus in sewage is currently recovered around the world, but soaring fertiliser costs mean it is now far more economical to do so.
Bryan Spears, professor at the UK Centre for Ecology and Hydrology (UKCEH), and a lead author of the most detailed report yet on the phosphorus problem, said: “Phosphorus could push us to the brink of a food security crisis. It is a finite resource, and it is overused in developed countries while developing countries do not have enough. It is a major cause of pollution as it upsets the ecological balance [in waterways]. Phosphorus pollution also threatens drinking water supplies.”
He said that phosphorus supplies were rising sharply in price, which would threaten food security if governments did not act to reduce the waste of phosphorus in our farming systems, and encourage its recycling from sewage and other sources.
The report, written by 40 international experts, led by UKCEH and the University of Edinburgh, shows that much more could be done, and at low cost, to recover phosphorus.
Prices have soared from about $240 (£192) a tonne to more than $900 a tonne for some forms of phosphorus-bearing rock, as the Ukraine war has disrupted fertiliser production. Phosphorus rock comes from only a handful of countries, chiefly Morocco. Most fertilisers use a mixture of phosphorus, nitrogen and potassium (NPK), and Ukraine and Russia are both major fertiliser suppliers.
The high prices for fertiliser have left farmers nursing big losses, unable to plant crops, or facing smaller yields. Food prices for consumers, already affected by supply problems, and the knock-on impacts of high energy prices, are rising further as a result.
The CEH scientists said farmers could also save money, and reduce the waste of phosphorus, by using fertiliser more efficiently, as most of the phosphorus in fertiliser is now wasted in runoff. This can be as simple as targeting fertiliser at crops and injecting it in the soil, and avoiding its use just before heavy rain is expected.
The report, which represents the most detailed examination yet of the global phosphorus problem, recommends a 50:50:50 goal, of a 50% reduction in global phosphorus pollution driven by a 50% increase in recycling of phosphorus by 2050.
To achieve this, the scientists urge governments to improve wastewater treatment to remove and reuse phosphorus from sewage; to help farmers use more targeted techniques for using fertiliser; to encourage more livestock manure to be converted into fertiliser as an alternative to chemical fertilisers; and for people to eat less meat, which would reduce the amount of phosphorus currently used to grow animal feed.
A spokesperson for the UK’s Department for Environment, Food and Rural Affairs said the government was acting: “Phosphorus pollution into our rivers has reduced by 67% over the last two decades. We have proposed setting long-term targets in our Environment Act to further reduce phosphorus pollution from agriculture by 40% and from wastewater by 80% by 2037.”
CEH scientists estimate that the capital investment required in the UK to recapture phosphorus from sewage is about £1.6bn, which would easily be outweighed by the benefits in reusing the recovered mineral as a fertiliser.
One small but significant use for phosphorus is in drinks such as Coca-Cola, in which it is used as a preservative. Taking it out could cause changes in the taste, but an alternative would be to source phosphorus from recycling – which would have consumers effectively drinking a byproduct of urine.
Will Brownlie, a freshwater scientist from Edinburgh University who coordinated the report, said: “I would love if Coca-Cola could develop an alternative, to use recycled phosphorus – to take the pollution out of our rivers and lakes and turn it into a drink.”
Coca-Cola did not respond to the Guardian’s request for comment.
