Pulsing sound waves can help remove microplastics from ocean, study reveals

The team has created a prototype made of eight mm steel tubes and a transducer (a device that converts one form of energy into another). When the transducer was activated, it sent pulsating sound waves through the metal tube. As a result, the particles moved and vibrated, allowing small pieces of plastic to accumulate in flowing water as they passed through the system. For instance, consider a loudspeaker that vibrates the ground, thereby bouncing dust particles toward each other.

“Because acoustic forces can push particles together, I wondered if we could use them to aggregate microplastics in water, making plastic easier to remove,” said Menake Piyasena, the principal investigator of this project, in a press release.

This device is intended to collect microplastics of varying sizes. And could be scaled up to filter large volumes of water. Previously, scientists conducted similar types of experiments in the lab, but with a smaller volume of water and microplastics only ten microns wide. Most microplastics in the environment, according to the researchers, are slightly larger than this size.

The team conducted initial experiments using polystyrene, polyethylene, and polymethyl methacrylate microplastics. The two tubes worked in tandem to segregate the microplastics of various sizes. The device was able to remove over 70 percent of the small plastics and 82 percent of the larger-size microplastics, according to the results. They also tested the prototype by collecting water from the Rio Grande River and a pond on the New Mexico Tech campus.

The device would cost approximately seven cents to operate for an hour and a half to clean one liter of water. Following these initial experiments, the team plans to test the prototype on a larger scale, focusing on cleaning ocean water.

The research was presented at the spring meeting of the American Chemical Society (ACS).