We’ve been told time and time again that we need to minimise our waste and recycle our rubbish wherever we can. But why is this so important? Well, while some of the waste we bury in landfill sites will eventually rot – a decomposing process that often produces methane gas, which contributes to the greenhouse effect incinerating waste also causes problems, as toxins are released into the atmosphere which contribute to acid rain and pollution.
And yet waste is inevitable. Luckily, innovators like Stockton-based waste and recycling business Scott Bros are working hard to use this to our advantage – with the help of groundbreaking research at Teesside University.
‘We’ve got two projects running with Scott Bros,’ explains Dr Paul Sargent, Senior Lecturer in Civil Engineering (Geotechnics) at Teesside University. Both of the projects are focused on discovering whether our everyday waste can be turned into materials we can go on to use in construction – waste which, somewhat surprisingly, includes soil and earth. ‘One is to find a use for a clay-based “filter cake” produced by their wash plant, and the other is to discover uses for mixed-plastic waste. Ultimately, we’re trying to improve the circular economy.’
‘Scott Bros are a haulage company, so they do a lot in the way of site clearance,’ says Paul. ‘They tend to take in a lot of earth waste that would normally go to landfill. But rather than sending it to landfill, they take this bulk earth to their own facility, where they have a piece of equipment called a Soil Washing Plant. This separates out all the different particle sizes – from the really fine-grain stuff, like clay, all the way up to gravel – and cleans them.
‘The UK’s supply of natural sand and gravels is getting a wee bit smaller, because they’re in high demand, so Scott Bros are trying to encourage more people to use these washed waste materials as construction aggregates. There’s a very clear use for the sand and the gravel – we can use them in concrete and pavement sub-bases – but there is something left over that we don’t yet know what to do with, which is (and I quote) “a silty, clay slop!” Scott Bros weren’t sure what they could do with it and that’s where Teesside University came in. We’ve found that we can actually convert this slop into a harder, cementitious material which actually has quite a high compressive strength, and one of the key things is that this material is 85 percent waste-based, which is quite a staggering figure.’
The beauty of their research projects lies in its simplicity. As a haulage company, Scott Bros are already collecting the waste, which they can then easily transport to Teesside University for tests. And yet the findings that may arise from this partnership could go on to change the face of the UK’s fight against global warming – particularly if they find a way to reuse the currently un-recyclable (and potentially toxic) mixed plastics.
‘Post-consumer, mixed-plastic waste is a problem,’ Paul admits. ‘Whilst, for a while now, we’ve been able to recycle some plastics, like your milk bottles, there are others which are more complicated in terms of their chemistry. These are mixed-plastics – the films that you’ll have in most of your sealed food packaging, for example. Scott Bros take in a lot of plastic waste, so they’re bringing some of that waste to us to experiment with.
‘We’re looking to implement a process called pyrolysis, which involves heating up a material in an environment that has no oxygen, to reduce its volume – sometimes by up to 85 percent. Our thinking is that this process could also separate out the components that make up the plastic. For example, if we could separate out the mineral oils, could these then be re-used as a fuel? Or could we use them in construction products like tarmac? This is all speculative as we are at the very beginning of this project, but it could be possible. After pyrolysis, you’re also likely to be left with a kind of charcoal, so we’re wondering how we might be able to use that too, because it may be that it’s quite carbon-rich.
‘Within the next 10–20 years, we need to be in a position where we’re relying a lot less on traditional construction materials, which use a lot of energy to make and also emit a high level of carbon dioxide, and are using materials that aren’t just partially reused waste, but have been made using entirely reused waste instead. The two projects we’re working on really showcase the capabilities that we’ve got here in the North East, and the fact that we’re at the forefront of what is an international effort.’