Current negative publicity surrounding potential risks from microplastics and viruses associated with biosolids is based on research conducted under experimental conditions that do not adequately replicate those in the field, such as the use of excessively high microplastic concentrations and studies in very small volumes of soil (microcosms). As a result, they may provide misleading information on the actual risks posed by biosolids in real world conditions. It is therefore imperative that industry, regulatory bodies and policymakers have a robust scientific evidence base on which to make informed decisions about the use of biosolids in agriculture as sources of nutrients and organic matter to benefit crop and grass production.

This project aims to address three key technical challenges:

1. How do microplastics and viruses transit through the wastewater treatment process and are there interactions between the two?

2. What is the level of accumulation of microplastics and viruses in agricultural land?

Challenges 1 and 2 were achieved by repeated measurements of the microplastic and virus content of raw sewage (influent) and final product (treated biosolids) from nine different wastewater treatment plants. The biosolid treatment methods included conventional anaerobic digestion, advanced anaerobic digestion, lime stabilisation and thermal drying.

3. How do microplastics and viruses impact soil health and crop quality?

This was answered by setting up a replicated field plot-scale experiment, where different biosolid products (following a range of treatment methods) were applied to a sandy loam soil and sown with a new grass ley.