Eel-Like Envirobot Detects Water Pollution By Swimming Through It

Water pollution is a big problem all over the world, and it’s a difficult one to address, as there are many factors that can cause it, often hard to pinpoint. Researchers from École Polytechnique Fédérale de Lausanne (EPFL), the University of Lausanne and other institutions were looking for a new way to detect water pollution when they developed the Envirobot, an eel-like robot that swims through water and returns information about what’s causing problems. The autonomous robot’s presence in the water never causes further harm – it was designed to swim in a way that doesn’t stir up mud or disturb aquatic organisms, and the information it provides could allow scientists to better address the issue of pollution in our waterways.

The research team used 3D printing to develop the robot, which is almost 1.5 meters long and is equipped with chemical, biological and physical sensors. The team has been testing it in Lake Geneva; one recent test involved diffusing salt into the water, which changes its conductivity. The robot then swam through the salt-contaminated area, mapped the variations in conductivity and generated a temperature map.

“There are many advantages to using swimming robots. They can take measurements and send us data in real-time – much faster than if we had measurement stations set up around the lake. And compared with conventional propeller-driven underwater robots, they are less likely to get stuck in algae or branches as they move around. What’s more, they produce less of a wake, so they don’t disperse pollutants as much,” said Auke Ijspeert, Head of EPFL’s Biorobotics Laboratory (BioRob). “The Envirobot can follow a preprogrammed path, and has also the potential to make its own decisions and independently track down the source of pollution.”

The Envirobot has a modular design, and each module contains a small electric motor that changes curvature, allowing it to swim like an eel. It can also be easily taken apart for transport or to change its length as needed. The modules all contain a type of sensor; some measure temperature or conductivity, and others are filled with biological material or organisms. Those modules fill with water as the robot swims, and the reaction of the organisms indicates whether certain pollutants are present, as well as the overall water toxicity. These biological sensors include fish scales, tiny crustaceans and bacteria.

“For example, we developed bacteria that generate light when exposed to very low concentrations of mercury,” said Jan Roelof van der Meer, Project Coordinator and Head of the Department of Fundamental Microbiology at the University of Lausanne. “We can detect those changes using luminometers and then transmit the data in the form of electrical signals.”

The team also uses Daphnia, a type of small crustacean that constantly moves around. One group of the creatures is kept in a compartment filled with clean water, and the other is exposed to the polluted water.

“The Daphnia’s movement is affected by water toxicity. By comparing changes in their movement relative to the control group, we can get an idea of how toxic the water is,” said van der Meer.

The fish scales, meanwhile, are grown directly on electrodes. When toxins are present in the water, they disturb the cells, which no longer touch each other, interrupting the flow of electricity.

Only the conductivity and temperature sensors have been tested in the lake; tests of the biological sensors have only been carried out in the lab so far.

“We obviously can’t contaminate a lake like we do the test water in our lab,” said van der Meer. “For now, we will continue using salt as the contaminant until the robot can easily find the source of the contamination. Then we will add biological sensors to the robot and carry out tests with toxic compounds.”

Eventually, the team aims for the robot to be able to detect heavy metals like mercury or other toxic compounds. The project is being funded by the Swiss Nano-Tera Program and involves the University of Applied Sciences and Arts of Western Switzerland and the Swiss Federal Institute of Aquatic Science and Technology, in addition to EPFL and the University of Lausanne. You can learn more about Envirobot here.

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[Source: EPFL / Images: Alain Herzog/EPFL]