New research into recovering phosphorus from sewage

By Kenneth Macdonald
BBC Scotland special correspondent

  • Published
Media caption,
Tanks of waste water and microscopic green algae are used to capture the phosphorus

Scottish researchers are working on new techniques to recover phosphorus from sewage.

It is part of an EU-funded programme to recycle and conserve a vital element essential for food production.

The planet's reserves are diminishing amid a warning that we may have reached "peak phosphorus".

A team at Glasgow Caledonian University are recovering the chemical from waste water, microscopic plants and some wool.

It's right up there on the periodic table of the elements - atomic number 15.

It's the stuff that ensures safety matches strike when we want them to - but does not ignite the whole box in our pocket.

So good news if you're a fan of peat fires and/or scented candles.

But how much do we really need phosphorus?

Image caption,
The project aims to recapture discarded phosphorus from waste water and sewage sludge

More than many of us may realise. It's an essential part of our lives.

It's in our cells. In fact - just for once - it's not an exaggeration to say it's literally part of our DNA.

Most importantly it's an essential ingredient of the fertilisers that put food on our tables.

Whether it's fruit, vegetables or the plants we use to feed livestock, they all need phosphorus.

And unlike nitrogen, that other element essential for growth, we can't pluck it out of the air.

It has to be mined in a relative handful of countries, not all of them beacons of stability.

Reserves diminishing

Prof Ole Pahl, of Glasgow Caledonian University, is among those facing up to the problem.

"The statistics say that every person uses about 22kg of the original material - in rock - per year," he says.

"So multiply that by the world population and you can imagine how much of it we use."

The planet's phosphorus reserves are limited and diminishing.

Our bodies use only a little of the phosphorus contained in the food we eat.

The rest of it we are pouring down the drain.

It goes into our sewage and is washed irrecoverably out to sea.

But perhaps not for much longer.

Image caption,
Dr Ania Escuero said the algae do not need much light

Glasgow Caledonian's researchers are part of an EU-funded project called Phos4You. It aims to recapture our discarded phosphorus from waste water and sewage sludge.

On the continent, with big population centres, that could be achieved on an industrial scale.

Scotland's problem is that it has relatively few big sewage treatment works. Much of our waste is handled by smaller facilities - and a whole lot of septic tanks.

So if Scotland is to recover significant amounts of phosphorus from waste it'll have to be done on an appropriate scale.

In a laboratory at Glasgow Caledonian, PhD student Lena Reichelt is working towards that using two tanks of waste water - sourced from Paisley - and myriad microscopic green algae.

'Really resistant algae'

In one tank the algae have turned the water a uniform deep green. It's not unattractive if you avoid thinking about what it actually is.

In the other tank the water is clearer. There the algae are clinging to some furry sticks which are weirdly suggestive of evil lollipops.

"In the first tank it's green because the algae are suspended," Lena says.

"In the other one, the algae are getting attached to a biofilm and actually consuming the phosphorus.

"In the end we're trying to recover the phosphorus from these microalgae."

The biofilm on which the algae are capturing the phosphorus - the stuff that is making the sticks furry - is nothing more sophisticated than wool.

Image caption,
Phosphorus is used in safety matches

It's a technology likely to suit Scotland's smaller-scale sewage system.

But as research assistant Dr Ania Escuero explains, it's the algae that are special. They've been sourced from a badly-polluted river in Spain.

"They are really resistant and they don't need much light," she says.

"So in a place like Scotland or north west Europe in general that's really interesting.

"Everyone thinks that we are crazy because we are growing microalgae in Scotland with no light.

"But these are specific algae. With a lot of light they get inhibited. So they prefer to be a bit in the darkness."

More sophisticated

Researchers at the University of the Highlands and Islands are also involved in this pan-European effort to create a phosphorus cycle.

In some ways it's what farmers have always done when they spread muck on their fields.

But it promises to be a lot more sophisticated - and to raise sociological, even aesthetic, questions.

Prof Pahl says: "What we are trying now is to see whether people will be happy with a closer loop, closer to their own home, where you could almost know the neighbours that would have produced this phosphorus.

"Are you happy to put that back onto your land?

"Maybe not to grow salad, but to grow forestry, to grow grass that then our cows can graze on."

If both the scientific and the societal questions can be answered to everyone's satisfaction, we may be able to prevent this vital element being lost at sea.

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