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Breaking down household waste and reforming it into products

We have been separating our waste for many years, but a large part of the waste stream cannot be recycled. Scientists at the University of Twente are researching, in collaboration with companies, how you can make new products from so-called complex and ‘wet’ waste streams. This involves efficiently isolating the chemical components that are then used in new materials. This spring sees the start of the project ReBBloCS – Renewable Building Blocks from Complex and wet waSte – with a grant of 3.8 million euros from the Netherlands Enterprise Agency.

Plastics, metal or fibre – our waste is a tremendous source of raw materials and biofuels. At any rate, if you can extract them. It continues to be a challenge to extract useful components from residual waste, as well as residues from agriculture and wastewater treatment – generally wet waste streams. Even though they definitely contain reusable components, the majority of these waste streams end up in the incinerator.
Professor of Separation Technology Boelo Schuur and Professor of Sustainable Process Technology Sascha Kersten of the University of Twente are trying to change that. They are involved as program directors in the ReBBloCS project, a collaboration of scientists and companies linked to the Institute for Sustainable Process Technology. They include major companies like Tejin, SABIC and DOW Chemical Company that need raw materials from recycled sources, and companies, many of them small start-ups such as BioBTX and Recell, that have the technology to take the required chemical steps but cannot yet do so on a large scale. Over the next four years, these parties in ReBBloCS will be pooling their knowledge and looking for ways to transform residual streams, that today are merely waste, into raw materials for the chemical industry and into biofuels and biobased plastics.

Break down and build up like LEGO

Schuur compares our waste to LEGO. You can break down a LEGO model into bricks and make something new from them. He wants to do that with our waste as well, in a chemical sense. In fact, chemical transformations have long been carried out in industry, but those processes usually work with relatively clean and – in particular – stable supply streams. That is fundamentally different if you use waste as a supply source. Its composition varies from one day to another, from one garbage bag to another. Even a relatively homogeneous waste stream such as sorted plastic waste causes problems. It often includes substances such as PVC that contain chlorine and other plastics with flame retardants based on bromine. These substances can form hydrochloric acid or hydrogen bromide that damage machines in a factory, Schuur says.
If you take extra steps in the processing, you can remove or neutralise such contaminants. That is how the researchers intend to make the recycling processes better able to withstand supply streams that vary in composition and quality. Potential solutions are to use micro-organisms that convert substances via a process known as hydrolysis and to use high-temperature chemical transformations via gasification processes or pyrolysis.

High-quality products

In ReBBloCS, a PhD candidate and a postdoctoral researcher at the University of Twente are studying the separation processes before and after the gasification processes and pyrolysis. The aim of this is to isolate and produce different chemicals from a waste stream, including raw materials for high-quality products, such as plastics, adhesive, paint and a strong aramid fibre.
As well as developing technologies, the researchers want to help companies choose the recycling processes that suit them best. “Companies that want to become greener and use waste streams often don’t know what chemical processes are the most suitable”, says Schuur. “This depends on the composition of the waste stream. We are developing a tool that helps them choose the best recycling technology.”

J.C. Vreeman (Jochem)
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