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.

Sewage sludge is the solid part of sewage that settles out and is treated separately from the wastewater. Most UK sewage sludge is treated by Anaerobic Digestion or Advanced AD. Treated sewage sludge is often termed biosolids.

This process produces biosolids that can be readily transported and stockpiled, with a relatively low odour profile. This has played a role in the rise of agriculture as the primary outlet for UK biosolids. Other outlets, such as incineration or landfilling generally have higher costs.

Around 3.5 million tonnes of biosolids are produced in the UK each year, with 87 per cent spread on agricultural land. Although this amounts to a significant logistical operation for water companies, biosolids make up just under 4 per cent of the organic materials used in British agriculture.

In 2023/24, in England and Wales, biogas from sewage sludge was used to generate c.900 GWh of renewable electricity, enough to power the homes of a city the size of Leeds. And, approximately 40,000 tonnes of phosphate and 6000 tonnes of available nitrogen are supplied to agriculture each year in biosolids, providing valuable nutrients to farmers.

However, there are growing concerns that substances such as microplastics and PFAS are ending up in sewage sludge and are not well-degraded by treatment. As a result, using biosolids in agriculture has the potential to release the substances they contain into the environment. There are concerns that substances could then be taken up by crops or livestock and enter the food chain.

At present, regulatory limits on biosolids are limited to a small list of heavy metals and there is an overdue commitment to take biosolids regulation into the Environmental Permitting Regulations which would enable better control and management.

The challenges posed by contamination of biosolids by these substances mean there is a need evidenced, strategic planning and regulation of the right sustainable approach to managing biosolids for the long-term, so risks are appropriately managed and the water industry can plan accordingly.

This briefing and position statement discusses the issues.