Microplastic particles smaller than 5 mm in diameter are found in all waterways of the world and can be harmful to humans and aquatic life. In the two-stage system created by the researchers, most of the plastic particles are effectively removed from the water samples using steel tubes and vibrating sound waves. The group will report their findings at the 2023 spring meeting of the American Chemical Society (ACS).
Most waterways, from streams to the Arctic Ocean, have colored plastic debris floating below the surface. Less than 5 mm wide and subtle, these microplastics have the potential to harm aquatic life, plants and humans alike. That's why researchers are developing strategies to get rid of them and stop them at source. A large part of the plastic particles in real water samples can now be removed, thanks to a two-stage system created with steel tubes and vibrating sound waves, according to a team's research.
The researchers will present their findings at the spring meeting of the American Chemical Society. (ACS). The hybrid ACS Spring 26 meeting, which will be held from March 30-2023, will feature more than 10.000 presentations on various research topics.
According to the project's principal investigator, Doctor Menake Piyasena, “this idea came from a discussion I had with a colleague who said we needed new ways to collect microplastics from water.” “I wondered if we could use acoustic forces to collect the microplastics in the water, so we could make the plastic easier to remove because they can bind the particles together.”
The most popular method used to remove these components from the water is filtration. For example, washing machine outlet filters can prevent clothing fibers from getting into the waste water. Filters must be cleaned frequently as they can become clogged, making this process expensive on a large scale.
Another alternative is to use acoustic forces or sound waves to condense plastic particles in moving water. These forces transmit energy to surrounding particles, causing some to vibrate and move. Think of a loud speaker that shakes the floor and sends specks of dirt and dust flying in all directions. To separate biological particles from fluids, for example, to separate red blood cells from plasma, scientists have used this phenomenon before.
This method has recently been used by some teams to separate microplastics from samples they have produced in the lab using only distilled water. But only modest amounts of water were used for this task.
One of the researchers, Nelum Perera, claims they also use microplastics, which are only tens of microns wide—smaller than the width of a human hair.
Presenting the results, Perera says: “I've read that most of the microplastics in the environment are bigger than that. Therefore, I aimed to create a tool that could be used for most sizes while being scalable to achieve real-world goals.
Perera built a proof-of-concept system using 8mm wide steel tubes connected to an inlet tube and multiple outlet tubes to handle increased water flow rates. He then attached a transducer to the side of the metal tube. When the transducer was turned on, it sent ultrasonic waves down the metal tube, creating acoustic pressures, making it easier to trap the microplastics as they moved through the system.
Piyasena says the prototype device is less complex than traditional filtration techniques, as it doesn't clog as quickly as a filter.
In their initial experiments with polystyrene, polyethylene and polymethyl methacrylate microplastics, the researchers found that smaller (6 to 180 m wide) particles behaved differently than larger (180 to 300 m wide) ones in the presence of acoustic pressures. Particles of both sizes were piled in the middle of the channel and exited the central outlet while clean water gushed from the outlets on both sides. But when fabric softener or laundry detergent was added to the water, larger particles condensed to the sides and exited the side outlets, while the middle outlet released clean water.
Based on these findings, the researchers set out to work on a system that could take advantage of these various gestures. Two steel tubes were joined back-to-back: In the first stage, small microplastics less than 180 meters wide were removed, while in the second stage the water stream containing the remaining larger microplastics was cleaned. “We cleaned more than 70% of small plastics and more than 82% of large plastics with this method,” Perera says.
Perera and Piyasena collected water from the Rio Grande River and a pond on the New Mexico Tech campus to demonstrate the viability of the two-step method in practical settings.
They used filters to remove large contaminants from all samples, leaving water containing dissolved substances that may have affected separation. The water was then covered with tiny plastic particles. Plastic particles were eliminated from ambient water samples using an acoustic device, just as they were from pure water. According to Perera, the prototype takes about an hour and a half to clean a liter of water and costs about 7 cents an hour to run.
The next step for the researchers is to build a system of larger tubes, or bundles of multiple tubes, and test the system on unmixed real-world samples such as ocean water and washing machine wastewater. According to Piyasena, “We have shown that acoustic pressures can be used to densify a wide variety of microplastic sizes. Next we want to use real samples that already contain microplastics to show that this can be done on a larger scale.
Günceleme: 29/03/2023 10:54