Should we be putting sewage sludge on land anymore?

31 July 2025

There is growing – and understandable – concern and coverage over what is in the treated sewage sludge (biosolids) that gets spread onto farmland as a fertiliser. Government and the water industry need to plan for a different future.

The disposal of sewage sludge at sea was halted in the late 1990s. Since then the UK water industry has closely guarded recycling biosolids to land as fertiliser as its easiest and, on the face of it, most sustainable management option.

In the past, concern has related to contamination levels of metals, or whether it’s possible to regulate for digestion of food waste and sewage sludge together (doing so would be a more efficient way of producing biogas). Then there’s simply public opinion around the ‘ick factor’ of using digested poo to aid production of the food we eat.

In recent years the media focus has shifted to this practice as a transfer mechanism for worrisome pollutants such as PFAS and microplastics into our food production landscape, as well as the aged and lacking regulatory frameworks governing it. And this focus is ramping up.

The embattled UK water industry is nervously eyeing yet another sewage scandal. And without decisive action from both the industry and ministers (as distinct from the regulator, because reportedly the Environment Agency (EA) had asked the Department of the Environment, Farming and Rural Affairs (Defra) to give this issue greater focus), it could very well become that.

Circularity unsquared

Spreading nutrient rich, treated sewage onto land as a fertiliser and soil conditioner should be a great example of circular economy principles in practice. Around 3.5 million tonnes of biosolids are produced in the UK each year, with 87 per cent spread on agricultural land, amounting to around £45 million-worth of nitrate and phosphate input either cheaply or for free.

But that circularity relies on what goes into treatment works being realistically treatable. Unfortunately for water companies, they’re at the end of the pipe into which all manner of tricky-to-treat substances that works were never originally designed to treat are being disposed (like microplastics, forever chemicals, and other emerging pollutants). Because those substances are part of, or by-products of, our everyday consumer lives.

It’s up for debate how much water companies are potentially making things worse for themselves by additionally accepting relatively small volumes of commercial effluents (compared to domestic), for which there isn’t adequate regulation through the conventional sewage treatment train. Although, evidence shows that sewers serving only domestic sources also contain appreciable chemical concentrations (including PFAS) and in some instances higher concentrations than catchments that include trade effluent sources.

Either way, the virtuous circularity of this approach is tainted.

So what?

The problem with all this is that we don’t really know with great certainty how much is getting through and what the impact on the environment and on human health is. Additionally, how sewage sludge as a transportation mechanism compares to other means of exposure to chemicals like PFAS, which are in all manner of products from the textiles we wear, sit on and breathe the fibres from, to cosmetics including lipsticks.

But the body of scientific literature is rapidly growing and points to the chronic contamination of our land and seas with these and other materials as a challenge we need to get to grips with. Quickly, and preferably at source.

So, this is something Defra and its ministers need to engage with actively and with urgency. A review of the Environment Agency’s sludge strategy must be given fresh impetus. The government is developing a new regulatory regime for PFAS which should, in time, start to bear down on levels entering effluents and ultimately biosolids.

The Chemicals Investigation Programme (CIP) is seeking to better understand the chemical composition of sewage sludges and the risks associated with those chemicals not currently regulated for. This evidence-gathering will inform an overdue move of sludge regulation from the Sludge Use in Agriculture Regulations into the EA’s Environmental Permitting Regulations (something the recent Cunliffe Review recommended). The current round of the programme is set to run until at least 2027 and efforts to accelerate it should be explored.

Front foot

There are compelling reasons why a proactive approach to improving management of all these substances is important. The obvious one is that given the persistent and ubiquitous nature of microplastics and PFAS, it’s vital to avoid a toxic legacy of an on-the-face-of-it sustainable practice.

But also, because if it is decided that biosolids need to be disposed of in another way, it will take some time to put the necessary infrastructure in place. One of the most commonly cited alternatives is incineration. This is never popular with local communities and isn’t great from a carbon emissions perspective and may just mobilise PFAS in other ways. There may also be challenges with using existing waste incinerators, as the technology can experience operational issues above a certain proportion of sludge or biosolids in the feedstock.

A regulatory response does need to be evidenced and proportionate. Biosolids make up just four per cent of the organic materials used in British agriculture, with the majority made up by cattle slurry and farmyard manure. And only 1.6 per cent of the UK’s agricultural land area receives biosolids each year, on average. That’s not to in any way negate the need to manage things properly, for the long term.

As with other aspects of water management where pollutants are diffuse, this needs a systems approach to management. There needs to be a better understanding of all inputs into land and catchments of PFAS and other challenging contaminants, with appropriate use of producer responsibility and source control alongside end-of-pipe treatment by the water industry.

The water industry would do well to learn from its chastening experience on other aspects of wastewater management. Being evasive on the issue won’t work as a tactic to preserve the status quo. Investigative journalists and campaigners, aided by social media and other tools are too dogged for that.

But fundamentally this is an area where government has a moral duty to back its regulator, to understand the nature and scale of the issue, and work with water companies to set out a roadmap to an appropriate and sustainable long-term solution.

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CIWEM have recently published a new policy position statement on biosolids – read it here. We also have a wastewater and bioresources panel which is open to new members.

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Alastair Chisholm is director of policy at CIWEM