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.
Mrigakshi Dixit
Close-up shot of microplastic waste.
Close-up shot of microplastic waste.


Every year, large amounts of plastic waste are dumped into the oceans. Much of it forms microplastics, which are tiny fragments of barely visible plastic that are roughly five mm in size. 

The growing microplastic menace continues to pollute the oceans and can be toxic to aquatic animals and plants. Therefore, new technological solutions are required to combat the increasing presence of microplastics in the oceans.

Scientists from the New Mexico Institute of Mining and Technology have discovered a potential method for removing various sizes of microplastics from waterways and preventing them from ending up in the oceans.

Removing microplastics using soundwaves

Filtration is the most commonly used method for removing microplastics from water, but it may not be capable of meticulously capturing tiny plastic specks. The scientists used a different sound wave technique for this study.

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.

Pulsing sound waves can help remove microplastics from ocean, study reveals
Microplastics naturally scatter in flowing water (left), but after turning on sound waves, the particles concentrate along the tube’s sides (right), making them easier to remove.

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).

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