Charred hedge cuttings could wipe out runoff microplastics

Researchers have found that charcoal formed from hedge cuttings and other vegetation removed from roadsides can, in laboratory tests, all but eradicate harmful microscopic particles of plastic found in all road runoff water from where they can enter food and drinking water via rivers.

The laboratory testing was undertaken by RSK Group company, TerrAffix, and infrastructure firm, Kier, at Swansea University. They found that there were no traces of microplastics in suspensions of microplastics  – at concentrations found in road runoff – after they had been passed over charcoal formed from vegetation (biochar). The next step in the collaboration will be to look at how effective biochar is over time. That will be tested on the A417 project by Kier and National Highways.

Last year, the TerrAffix/Kier collaboration found that turning roadside vegetation to biochar on site can reduce carbon emissions generated by vehicles used in collection and removal by some 90%. Its laboratory findings suggest significantly greater benefit could be had from adding biochar treatment of road runoff to take out toxic microplastics. TerrAffix managing director, Mark Smith, said: “Now that the process to remove microplastics has been proven to be successful in the lab, we are, of course, keen to take it on the road to further demonstrate the process in the field.”

Head of environment and sustainability at Kier Transportation, Matt Tompsett, said: “We wanted to focus on a solution that could be deployed at scale within highway drainage systems. I had high hopes that biochar would be effective at removing microplastic, but the fact that there were no traces of microplastic is fantastic. 

“Globally, there are no published papers at all which look at road runoff and microplastic removal using biochar, so this research is breaking new ground.”

Making biochar deploys a process known as pyrolysis whereby organic material is turned into carbon by exposing it to high temperatures in the presence of little or no oxygen. Portable pyrolysis systems can be used to generate biochar at the roadside where in due course it may be possible to use it to treat runoff.