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Bachelor of Engineering students invent machine and transform waste separation

Plastic bags and household film are mixed with plastic egg boxes and yoghurt tubs in a trolley bin with "plastic" written on the top. Danes have never been better at separating their waste, but in fact they could be even better at separating and recycling plastic waste, and this would be a great benefit for the environment. With a new invention, two Bachelor of Engineering students have found an effective and inexpensive solution.

Photo: AU Foto/Ida Marie Jensen

A shaking machine built with four, staggered plates that run at angles to each other with a specific slope and a specific type of vibration. That’s the way to more efficient plastic separation so that soft plastic is separated from hard plastic to help the environment.

The idea comes from two students, Emil Buur Trads and Rasmus Dall Nielsen from Aarhus University School of Engineering, who invented the machine as part of their joint Bachelor of Engineering project.

- Society uses a huge amount of resources to separate plastics because we want to recycle as much as possible and thereby cut crude oil and carbon dioxide emissions to the atmosphere. We discovered at an early stage of our project that there is a potential to make waste separation more efficient than it is today, says Emil Buur Trads.

Soft plastics contaminate separated  waste and the work environment

Packaging from food and drinks, shampoo, cleaning products and bubble plastics are piling up at large separation facilities in Denmark and abroad. These facilities separate waste into different plastic types using sensor and robot technology, but employees also have to dip their hands into the garbage every day to remove the soft plastic from the hard plastic manually.

In terms of chemistry, soft plastics such as domestic film and carrier bags are a source of contamination, and they impair the efficiency of the separation process drastically, says Emil Buur Trads.

- Soft plastic is a welded material and has different properties than hard plastic. So it’s crucial for efficient recycling that the plastics are separated. Specifically, this means that the separation plant has to employ people to put their hands into the stinking waste. This is a problem for their work environment, and it also means that the rate of separation may vary, he says.

Simple, cheap and extremely efficient

If we could recycle more plastics than we do today, this would have a major impact on the environment. One kilogram of recycled plastic saves the climate from four kilos of greenhouse gases, or the equivalent of a power plant burning 30 kilos of coal.

There are already a variety of technological proposals for automated waste separation, but the students' machine is different because it is incredibly simple and therefore also very cheap. It has no sensors, robotic arms, artificial intelligence or camera technology. The two Bachelor of Engineering students’ shaking machine has proved to be extremely efficient, at 95 per cent in 200 laboratory experiments. The machine separates the plastic by means of a simple mechanical principle.

- The principle is called ballistic separation, and the soft plastic is shaken to one side, while hard plastic, glass and metal is shaken to the other side. The shaking ensures that plastics wrapped around other objects are also separated, explains Rasmus Dall Nielsen.

Combine harvester paves the way for plastics separation

The idea came from the countryside, where both of the students grew up. The technique is very similar to the way in which a combine separates grain and straw.

- When we first saw a separation facility, we thought it must be possible to separate the plastics more efficiently. We both grew up in the country and we could see the potential in working with the idea of separating waste according to the same mechanical principle as a combine harvester, says Emil Buur Trads.

The machine is still just a prototype, but after 200 laboratory tests, the efficiency it has demonstrated is very interesting in both an environmental and a financial perspective.

- The technology can solve a large part of the problem of separating plastics inexpensively and efficiently. This makes it possible to recycle more plastics and thereby reduce the overall environmental impact from our waste, says Rasmus Dall Nielsen.

Rasmus Dall Nielsen and Emil Buur Trads have set up the company TechKnow at the Aarhus School of Engineering's Startup Factory and their ambition is to commercialize the machine over the next few years.