Is the UK ready to close the loop on phosphorus?

Is the time right for water companies to start recovering phosphorus? Lucinda Dann explores what it will take to make nutrient recovery economic in the UK

The UK could produce its own phosphorus for use in essential fertilisers, and yet UK farmers are 100% reliant on imported fertilisers.

To date is has proved uneconomical for water companies to recover the phosphorus contained in wastewater and sludge. However, trade body Water UK has signalled that it wants the sector to work at removing the obstacles to the nutrients’ recovery over the next asset maintenance period (AMP 8).

In its Net Zero 2030 Routemap, it calls on the water sector to work with the agricultural sector and the Department for Energy, Farming and Rural Affairs (Defra) to develop the evidence case for the true value of recovered phosphorus to help raise the price or introduce incentives.

However, since the routemap was published the price of phosphorus has soared by 300% due to the Ukrainian war, changing the economic case for recovered phosphate.

While some in the industry think this could be enough to kickstart the industry in the UK, others believe that regulating the reuse of phosphate is essential.

Challenge or opportunity

Phosphorus in wastewater is currently a serious challenge for the water industry as it is the most common cause of poor water quality. Excess nutrients in wastewater is an issue for the environment due to it promoting excess algae and plant growth, known as eutrophication.

Food waste is one of the main contributors to high phosphorus levels in wastewater, but it can be removed by adding chemicals or using a biological process. The amount of phosphorus released from water company sewage treatment works was reduced in 2020 by more than 66% from the levels seen in 1995 due to the introduction of treatment to remove phosphorus.

However, this reduction has come at a serious cost – £2.1 billion, with a further £1.7 billion being spent during the current price control period PR19, which should increase the reduction in the levels released from wastewater treatment works to 88%.

But the phosphorus contained in wastewater could be an opportunity. Water companies could recover the phosphorus rather than removing it, creating a potential new revenue stream while also improving their carbon footprint.

According to 2013 figures, 85% of the phosphorus contained in human excreta and other human wastes in Europe was not recycled.

Recovered phosphorus from wastewater can be used in place of mined supplies to make fertiliser. Phosphorus is the second most important nutrient required for crop growth, with 80% of phosphorus being used for fertiliser production.

This would secure a domestic supply of this essential resource. Most countries around the world import all their phosphorus as the mineral is only mined in a few countries, and the UK is no exception. This makes it a particularly geopolitically- sensitive resource, as highlighted by the Ukraine war which resulted in sky-high fertiliser prices and global shortages.

“It would be very helpful to be more self-reliant from a geopolitical perspective. It makes sense for us not to be beholden on other places, to some degree quite politically unstable places, to get the phosphorus, so if we could recover it you would think it would be well worth doing,” says Peter Vale, carbon and circular economy architect, Severn Trent.

Mined phosphorus also has other issues. It often contains heavy metals such as arsenic, and it is finite – scientists estimate supplies could run out in as little as 100 years.

No progress

Creating a domestic renewable supply would clearly have a myriad of benefits, and yet all efforts to establish the practice in the UK have so far failed.

In 2013 the first reactor in Europe which could create phosphorus-based fertiliser from sewage was opened by Thames Water. The £2 million nutrient-recovery reactor was able to produce 150 tonnes a year of fertiliser by converting struvite into crystalline fertiliser pellets.

Struvite, or magnesium ammonium phosphate, is created when biological processes are used to remove the phosphorus rather than chemicals.

With phosphorus prices up 500% on 2007 levels, Thames hoped the reactor would provide a cheaper and more environmentally friendly alternative to mined phosphorus. Instead, the plant ceased operations several years ago and the technology has not been rolled out to any other treatment works. Severn Trent also failed to make the figures stack up at their full-scale plant.

Although recovery from effluent has yet to get off the ground, it can be said that UK water companies do already recover phosphorus in the form of sludge, which is applied to agricultural land. But recovering it in mineral form would be better for several reasons, says Vale.

Firstly, the amount of phosphorus in soils varies across the UK, with some areas having quite high levels. This is likely to limit or even stop the application of sewage sludge to land in some areas, he says.

This means sludge must be transported around the country to where it is applicable, and the significant water content means transport emissions for sludge are much higher than they would be for concentrated phosphate. Sewage sludge can also only be applied at certain times of the year – limitations which would not apply to concentrated phosphorus.

Making the business case

Now, a decade later both companies are having another go at making phosphorus recovery work, in part due to the increase in fertiliser prices. “We are now looking at it again because we think the time is right. Arguably we went too early, when the value of struvite was very low and it was hard to make a business case to do it,” says Vale.

Fertiliser prices were already at historically high levels before the Ukraine war due to rising crop prices following the end of Covid restrictions, high natural gas and coal prices and a reduction in production capacity, according to the International Food Policy Research Institute.

Russia produces 11% of global phosphorus supplies, so the outbreak of war sent prices soaring due to uncertainty about exports, and the effect of economic sanctions on the countries. Fertiliser prices had increased by nearly 300% by April 2022 on December 2020 levels. While prices have now dropped, they are still 150% higher than they were at the end of 2020 and are unlikely to drop much further due unless energy prices also reduce.

Vale says the first waste stream the industry is likely to try and recover the nutrient from is sludge liquors, as the technology is mature. However, this will initially require water companies to be using a biological process, where as the majority of the industry is reliant on chemicals. Options for chemical users are becoming available though, says Vale.

“The revenue possibly is now sufficient from struvite to make the case, particularly if you look at it from the perspective of if you don’t take it out from the sludge and that restricts sludge to land, then that reinforces the case to do it – maybe that’s another thing that’s changed.”

In the future water companies should be looking to recover phosphorus from wastewater before it is treated as this will allow much more of the nutrient to be recovered, he adds. To this end Severn Trent has been working with Cranfield University on absorption ion exchange type processes.

“The technology is not as mature but there is ongoing research which will open up great potential opportunities directly from sewage,” he says.

Thames will be looking at recovering phosphorus as part of its £6 million Water Breakthrough Challenge project. The Transforming the Energy Balance of Wastewater Treatment initiative is looking at decarbonising water treatment but will also look at recovering beneficial resources, such as phosphorus and nitrogen.

The nutrients will be removed via absorptive methods, where they will be captured on granules and these then investigated as a product for industrial applications or agriculture.

A Thames Water spokesperson said that the project, which will be using an anaerobic process, is currently in the delivery phase and kick-off is expected towards the end of 2023.

Other barriers

A backdrop of high fertiliser prices and uncertain supplies is likely to be essential to UK water companies being able to get the ball rolling on recovering phosphorus.

However, even higher fertiliser prices may not be enough, given that Danish water company Aarhus Vand says it would not be able to justify the investment in resource recovery planned at a new innovative wastewater treatment works in Denmark without outside investment.

Aarhus Vand’s senior project manager, wastewater resource facilities, Morten Rebsdorf, said the opex savings alone were not enough, even though the company has been able to secure a decent price for its phosphorus with a fertiliser company.

The company is planning to build what it claims to be “the world’s most resource efficient wastewater treatment plant” in Aardhus to replace three existing plants and hopes to produce nutrients from wastewater to an “unprecedented extent”.

While fertiliser prices are high, they have not been high enough for the company to keep one of its two existing struvite plants in operation as it was producing too little yield to be economical.

While price and technology maturity are two important factors in determining whether recovering phosphorus is a possibility, there are other issues that will need addressing.

“We are also in the process of forming a working group to facilitate collaboration between the water companies, academia, regulators, and industrial partners. The working group will aim to develop a framework which removes the barriers to the full-scale adoption of nutrient recovery from wastewater,” says a Thames Water spokesperson.

“The impact of this focus group could inform regulatory change and build awareness of the challenges associated with nutrient recovery to lay the foundations for new markets for recovered end-products.”

A major report produced by the ‘Our Phosphorus Future’ project in 2021, which saw 100 scientists and industry experts from around the world work together on the subject, says that a market for recovered phosphorus products is the most important determinant for success.

It adds that a lack of tax incentives or support for farmers to adopt sustainable measures has been a significant barrier to the establishment of a market, but Vale believes that UK farmers are now open to utilizing products.

“Is there a market? I think for phosphorus clearly there is. Farmers are now really quite receptive when we have talked to them about organic fertilisers.”

One of the other issues is the difficulties water companies face in achieving end of waste status, which allows waste products to be recognized and sold as a secondary raw material, for their phosphorus-based products.

While this is possible to achieve for recovered phosphorus, with a struvite-based product achieving the status in 2010, Vale says the process could potentially be “a bit of a blocker” and could be made “less burdensome” for water companies.

“If between water companies and the regulators we can find a way of just making it a bit easier then it would really open up the market,” he says.

Regulation

While Water UK talked about the possibility of introducing incentives, the Our Phosphorus Future report has gone further and called for phosphorus recovery to be regulated, with global binding agreements being seen as a next step.

The worldwide lack of policy support for recovering phosphorus has been a major barrier to the building of commercial markets, it says, adding that market price should not define the economic feasibility of phosphorus recovery. Instead ‘polluters’ should share the cost of recovery, with the consumption of natural resources being taxed.

One government which has decided to go down the regulation route is Germany, which has set a target to thermally treat sewage sludge to recover phosphorus from 2029.

Given the lack of technological options available for phosphorus recovery when chemicals are used, the introduction of regulation is likely to encourage an increase in incineration, which the UK may not want to do, says Vale. However, he believes UK water companies will start to recover phosphorus without regulation.

He expects to see a handful of plants in the next five years but admits that widespread implementation without incentivization is likely to take a while and is also likely to be at a slower pace than other parts of the world.

“Whether you need that carrot or stick approach to really incentivize it and move it forwards – maybe. I’m definitely of the view that there is a really compelling reason to do this, and we should be doing this.

“Mandating is an option, incentivizing is an option, or it might be just reducing the regulatory burden and making it easier to do then you don’t need those incentives it just makes good sense for a water company to do.”