Can banning plastic straws really save the sea turtles? A group of ETH students has a more ambitious project to reduce marine plastic pollution: With their Autonomous River Cleanup platform, they want to filter plastic out of rivers, before it even reaches the ocean. Look out for their prototype on the Limmat this summer! by Riccardo Giacomello

Over five trillion plastic particles float in the oceans – far more than the number of stars in our galaxy. Together they exceed the weight of a quarter million tons. This affects not only the marine fauna, but also us humans: “On average we consume around five grams of plastic per week, via microplastics in our drinking water and sea salt as well as the consumption of seafood. This is equivalent to one credit card”, says Hendrik Kolvenbach, postdoc in space robotics at ETH. “Man can fly to the moon, but cannot keep the waters of his home planet clean.” This paradox motivated him to contribute to the project ARC (Autonomous River Cleanup). Its ambitious goal is to rid the world’s rivers of plastic waste.

Students take action

The project is run by students of ETH who share a common motivation: to develop a bachelor-, master- or semester-thesis that has particular relevance for real-world issues and is concerned with sustainability. They have diverse backgrounds such as energy science, mechanical engineering, or material science. Each of them works independently on their part to the solution within one of the three components of ARC: the detection of plastic waste, its horizontal and vertical concentration, and its extraction and sorting on a vessel or a platform. For instance, Adrian Ensmenger dedicates his master-thesis in fluid dynamics to a bubble barrier that concentrates plastic waste in rivers. Including the volunteers who help with the technical implementation, a total of 18 students are involved.

On the lookout for further partnerships

“It’s exciting to work with such a motivated team”, says co-leader Ariane Gubser, who coordinates the project in a duo with robotics student Fidel Esquivel. The latter founded ARC in 2019 together with test leader Joachim Schaeffer upon a request coming from industry to his professor Marco Hutter. The assistance of PhD students, postdocs and professors as well as the link to companies continues to be vital for ARC, especially with regard to funding. Financial support is currently provided by the Austrian firm Ecolymer, but the students are looking out for further possible partners. The practical tests that now follow the initial phase of theory and lab experiments will hopefully generate media attention and pave the way towards partnerships with industry and public administration. Many a company could even be interested in plastic waste as a resource. In summer, as a first step, the components will be tested in the Limmat, where the students hope to replicate the positive findings of the lab experiments. For this, they construct a platform of twelve meters length, much shorter than the original idea of a 31-meter-vessel. In a next step, further tests in other European countries will show how the technology could be integrated in local waste management systems. The final aim is to go global.

Polluted rivers are the source of the problem

But why do they tackle pollution in rivers instead of oceans? “Once plastic has reached the ocean, it quickly decomposes to microplastics and sinks, rendering extraction very difficult”, they say. “In rivers, the particles are much larger.” Moreover, rivers literally are the source of the problem: around 50% of all plastic waste in the oceans comes from them, and the ten dirtiest ones contribute 90% to this pollution. Such estimates are still very vague (and, by the way, ARC wants to improve them), but one thing is clear: here, concentrated action with limited effort can have a huge impact – and truly make the world cleaner.

Riccardo Giacomello, 25, 
studies comparative and international 
science. If he had any idea of engineering, 
he would probably join the project.