Using treated sewage sludge or ‘biosolids’ to enrich agricultural land has long been recognised as the most practicable environmental way of recycling it, providing benefits to both soil structure and fertility. However, a number of emerging hazards are being found in biosolids, including microplastics and pathogens, and there is increasing concern whether current controls are adequate to manage these.

A new UK Water Industry Research (UKWIR) project aims to establish a robust, evidence-based response to these concerns to ensure that biosolids can continue to be applied to agricultural land in a safe and sustainable manner.

The strategic UKWIR-funded project, SL01, is being led by environmental consultancy ADAS, working with a consortium of research bodies, including Cranfield University, the James Hutton Institute and the Animal and Plant Health Agency (APHA), as well as environmental consultancy Aqua Enviro, which has direct experience in biosolids’ production and quality control.

The project team will build on the wealth of existing information available on biosolids recycling to agricultural land by undertaking a targeted evidence-based review of the new and emerging issues. The review will take a holistic and systematic approach, and will include the published UK and international scientific literature investigating the range of potential substances that are, or could be, present in biosolids and which may pose a future barrier to its recycling to land. These include micro- and nano-plastics, fibres, organic chemical compounds, potentially toxic elements, nanoparticles, pathogens (human, animal and plant), transfer of antimicrobial resistance and, importantly, combinations of these.

The team will use their expertise to identify and prioritise key focus areas for further investigation, including an assessment of safe levels and limits in place in the UK and elsewhere, together with information obtained on future trends and signals.

The project is supported by an expert steering group drawn from UK water companies.