This summer, students from ETH Zurich will test various technologies on the Limmat for the automatic removal of waste. The Autonomous River Cleanup project is starting with rivers to tackle the global problem of marine pollution.

Robot removing plastics
A robotic arm with a camera will separate the waste according to material, with biomass returned to the water. (Photograph: ETH Zurich)

Millions of tonnes of waste end up in the world’s oceans every year. Plastics account for the largest share, decaying very slowly and threatening not only marine life and ecosystems, but also our health. Students at ETH Zurich have been working on finding technical solutions to alleviate this problem since 2019 as part of the Autonomous River Cleanup (ARC) initiative. The reason for the focus on rivers is primarily practical in nature. When plastic waste reaches the sea, it becomes much more difficult, if not impossible, to remove effectively, as it spreads widely and breaks down into smaller and smaller particles. “In rivers, the waste tends to be more concentrated and intact, which can make it easier to remove,” explains Fidel Esquivel, ETH Master’s student in Robotics, Systems and Control and a founding member of the ARC project.

Aiming for an efficient and intelligent system

The students have analyzed various technologies in the laboratory, which they will now test for the first time in a realistic environment and in interaction with each other. The test facility is located on the Limmat, alongside Zurich’s Platzspitz park. Up until the end of August, the students will examine the following three steps that are central to waste removal: concentration in one place, collection and sorting. In addition, they also aim to assess the quantity and composition of waste in the river by means of cameras at the Walchebrücke. The group will test various approaches for concentrating waste in one place, some of which will be combined – including a floating barrier and a barrier made of air bubbles. The students will use a conveyor belt to collect the material on the test platform, working to determine its optimal alignment. A robotic arm with a camera will separate the waste according to material, with biomass returned to the water. This will show whether the specially programmed deep learning algorithms recognize the objects correctly. Among other things, students will use floating GPS trackers to investigate the routes traveled by the waste. The results of the tests will subsequently be published on the project website.

The ARC project aims to increase knowledge in various areas, including how to quantify waste in bodies of water. The amount of plastic and forms of waste that end up in rivers and oceans is not precisely known, and various studies have reached very different estimates. In addition, the on-site analysis and sorting of waste is a new approach. “As a first step, we want to make sure that biomass can return to the river so that the ecosystem is affected as little as possible. But in the longer term, we aim to separate the waste by material and even by different types of plastic to be able to recycle it,” explains Joachim Schaeffer, a Master’s student in Energy Science and Technology at ETH, who is leading the tests on the Limmat. The ultimate goal is to ensure that the whole system is as energy-efficient and intelligent as possible. This would enable the intensity of the air bubbles and the speed of the conveyor belt to be automatically adapted to suit the detected amount of waste, as Schaeffer explains.

Expansion to more heavily polluted rivers planned

This spot on the Limmat was chosen as the test site for several reasons, one of which is its proximity to the main building and the surrounding ETH laboratories. In addition, there are no boats on this section of the Limmat and swimming is also prohibited. The installation was approved by the Cantonal Office for Waste, Water, Energy and Air. The impact on flora and fauna will be analysed further during the tests.

The results of this test phase will determine how the ARC project develops. The group aims to enhance its system based on the results and is planning further tests next year on larger, more heavily polluted rivers in Africa, India, and Southeast Asia. “The Limmat is not a heavily polluted river,” Esquivel emphasizes. “The facility is intended primarily for testing our system rather than for cleaning the river – although we have already filled a few rubbish bags.” ARC is supported by various industrial partners, maintains contact with the University of Natural Resources and Life Sciences in Vienna, and is interested in further partnerships, also on an international scale. The aim is to use those technologies that prove effective to offer individual solutions for different stakeholder groups and local conditions. This could involve clients from both the public and private sectors.

About the initiative

The Autonomous River Cleanup project was launched in 2019 by students at the ETH Robotic Systems Lab. Several of the 18 ETH students in the project team are completing a Bachelor’s or Master’s thesis or semester paper based on the project. The initiative is supervised by doctoral students and professors from five ETH laboratories and receives technological and financial support from the three industrial partners Ecolymer, Kindlimann Naval Architecture, and Phoenix Mecano.

Original Story by Leo Hermann

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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.

In this project, we are optimizing the energy production and distribution to operate the vessel with renewable energy.  The vessel is equipped with water turbines, solar panels, and fuel cells to takes on the challenge of a 100% emission-free vessel operation. We try to come up with a microgrid design that optimally harmonizes power generation and energy storage to tackle the main problem of green power technology: its irregular power yield. 

We aim to smooth out intermittent generation patterns to provide constant, reliable power at any time, any location, and in any condition.
At the moment, we are developing the overall system, we might be able to do some testing with similar, smaller-scale, components in the spring semester 2021.

The gripper project aims to develop a gripper to sort the collected waste and safely manipulate it as required by the river cleaning process. We are using a two-finger gripper with a gantry arm to conduct the above-mentioned tasks. The system is actuated electro-mechanically which allows better control and does not require additional resources for pneumatics on the boat. We found that the gantry arm is the only feasible solution regarding the dimensions of the boat.

To test various designs and evaluate whether a design would meet the requirements to sort a big variety of waste. The company Schunk has lent us an electro-mechanical two-finger gripper (PEH 30) for early testing of different finger designs. For this, a test setup has been designed and built. On this test station, the gripper remains in a fixed position and, various fingers will be tested, with respect to their ability to grasp different waste particles that are typically found in rivers.

The concentration stage of the Autonomous River Cleanup (ARC) system aims at blocking and concentrating plastic particles at a specified location to facilitate collection of the plastic waste. To this end, bubble curtains or bubble barriers represent a promising tool for particle concentration using flow shaping techniques.

The basic idea is simple! Air is pumped through a perforated tube lying at the bottom of the river, which induces bubbles at the orifices rising to the surface. This induces a vertical upward current and symmetric horizontal surface currents away from the bubble curtain. These currents are responsible for lifting submerged plastic particles and for blocking them at the surface.

The greatest advantages of bubble barriers are their promising ability to tackle submerged plastic beneath the surface next to floating waste and that they are unlikely to harm fish and allow the passage of boats.

As simple as the basic idea sounds, bubble curtains for plastic particle concentration are not well investigated. This makes designing such a system very challenging, but also very interesting, as many parameters must still be investigated and tested to understand how it can be used most efficiently. The current main challenge is to adjust all possible and interdependent system configurations by testing the bubble barrier in the water channel using standardized plastic particles. 

Further work on bubble barriers includes scaling up the system to the real-life application for testing in the Limmat and the Danube river including investigation of the interaction with all other ARC subsystems. Hopefully, bubble barriers are soon helping the Autonomous River Cleanup project working towards a cleaner tomorrow!

In February 2020 the ARC team met with its sponsor in Austria to work on potential concepts to clean river environments from plastic debris. We worked three days on ideation, concepts, and prototyping. Prof. Dr. Marco Hutter, Hendrik Kolvenbach, Karen Bodie, Giorgio Valsecchi, and Phillip Arm supported the team with their expertise

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