Recycled clay can account for up to 25% of the output produced when excavation waste is recycled via a washing process. This by-product commonly ends up in landfill.   

Now a £250,000 Knowledge Transfer Partnership (KTP) aims to develop Scotland’s circular economy approach further by undertaking significant research and development into creating new sustainable products from waste streams. 

The project will also include the creation of a hazardous soil treatment centre, the first of its kind in Scotland.  

Professor Gabriela Medero, a geotechnical and geoenvironmental engineer from Heriot-Watt University, will oversee the research. 

She explained: “As pressure mounts on global governments to react to the climate crisis, future regulation and legislation in the waste industry must be shaped to facilitate the adoption of a complete circular economy. Net zero targets are ambitious and will only be met through a reduction in the consumption of finite resources and a shift towards the use of sustainable products. Landfill, a symptom of the linear economy, can only be reduced if waste can be more effectively recycled into sustainable and innovative products. 

“Recycled clay is an exciting but currently unexplored material which could significantly reduce the waste we send to landfill each year. However, many barriers remain that prevent waste from major industries like construction being better utilised, including a lack of scientific understanding about material composition and the criteria for its use as set out by governing bodies like the Scottish Environmental Protection Agency (SEPA). 

“Through this project, we will rigorously test the properties and behaviour of the recycled clay to prove it meets Building Standards for product specification by performing a life-size case study on its performance attributes.  

“Additionally, we will investigate the use of spent oil shale and incinerator bottom ash as secondary aggregates, producing research evidence in the processing and application techniques which we hope will allay any concerns about their future use.” 

Spent oil shale has been used as a general fill material in road construction for decades. However, like recycled clay, this abundant material could be utilised for higher value applications.  

The use of incinerator bottom ash is currently constrained by regulation. Further research into this material and improvement processes could provide evidence to allow current restrictions to be relaxed. Incinerator bottom ash will become a more prevalent waste product in the coming years as an increasing number of ‘Energy from Waste’ incinerators are used in response to landfill bans. 

Family-owned recycling business, Brewster Bros specialises in completing the circle between Scotland’s growing construction, demolition and excavation waste stream and its increasing demand for construction materials.  

Scott Brewster, managing director, Brewster Bros, added: “The more ambitious and innovative we become when creating new products from waste, the more technical knowledge we will require from experts in their field. This Knowledge Transfer Partnership will not only enhance our company’s capabilities and offering, but also provide a vast body of knowledge that will benefit the wider industry as we collectively focus on achieving Net Zero targets.   

“A circular business model eases pressure on our country’s remaining landfill capacity and finite mineral resources, while helping our customers to avoid paying landfill tax and the aggregates levy. This will be even more important as businesses focus on a ‘green recovery’ in the post-Covid era.  

“By collaborating with Heriot-Watt University, we aim to overcome restrictions on use like waste legislation and obtain end-of-waste approval. However, understanding the true potential of these waste materials is also a key driver. We hope to discover if they can be used for higher-value applications or as raw materials in added value products.” 

Brewster Bros’ West Lothian site will host the new hazardous soil treatment centre which will use various remediation techniques to transform hazardous soils into a non-hazardous state so that they can then be recycled and reused, diverting them from landfill. 

According to SEPA, during 2019, 1.17 million tonnes of soils were disposed of, totalling 39% of all waste sent to landfill. As landfill bans, higher landfill tax and tighter environmental regulations are imposed, construction contractors will have greater need of such a facility for the safe processing of excavation waste in Scotland. 

The Knowledge Transfer Partnership is funded by Innovate UK and will run for two years. The team will include Wini Obande, KTP associate, who will conduct the research and Melis Sutman, academic support and Assistant Professor at Heriot-Watt University.