New Research: Pulsing sound waves can help to remove microplastics from water

Microplastics are dangerous as they are contaminating the entire ecosystem, and we need to introduce and implement measures to deal with them better. One such research presented recently proves to segregate microplastics from water.

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Dealing with plastic has already been so difficult, that introducing us to its micro form seems more of a horror dream. These tiny-sized plastic particles exist in oceans, in the guts of sea animals, and are now traceable in humans as well. Several filtration methods have been brought into experimentation to remove these particles, but having a size less than 5 mm makes it more difficult to segregate.

Recently a research team presented a technique at the American Chemical Society (ACS), showcasing new ways to collect microplastics from water.

A brief intro

Shinshu University scientists used sound to separate microplastics by experimenting with acoustic filtering to force microplastics towards a central channel. The researchers presented their findings at the American Chemical Society (ACS) spring meeting, which took place from March 26 to 30 and featured over 10,000 presentations on a wide range of science issues.

“The idea came from a suggestion from a colleague who said that new ways are needed to collect MPs from water,” says Menake Piyasena, PhD, the project’s principal investigator.

How microplastics are separated by soundwaves?

The device

The researchers built a proof-of-concept device made of 8-mm steel tubes coupled to one inlet tube and many output tubes. They then affixed a transducer (a device that converts one type of energy into another) to one side of the metal tube. When the transducer was activated, it sent ultrasonic waves through the metal tube, exerting acoustic stresses on microplastics as they travelled through the system, making them simpler to capture.

The concept

Plastic particles vibrate and move when acoustic forces, or sound waves, concentrate them in moving water and transfer energy to neighbouring particles. Consider a loudspeaker that shakes the ground, bouncing bits of dust and dirt towards one other. Scientists have already utilised this phenomenon just like separating red blood cells from plasma.

Hear from researchers

“Our proposed microfluidic device, which is based on hydraulic-electric analogy, has three 1.5 mm wide microchannels connected by four serial 0.7 mm wide trifurcated junctions,” said lead researcher Professor Yoshitake Akiyama of the Kyoto University . “A bulk acoustic wave with a resonance frequency of 500 kHz is used to align the microplastics at the centre of the middle microchannel. As a result, each junction required 3.2-fold microplastic enrichment, for a total of 105-fold enrichment in the device.”

Key Points

  • When independent experiments on grouped MPs were conducted, the collection rate for those sized 10 m, 15 m, 25 m, 50 m, and 200 m was greater than 90%. Further testing with different particle sizes (25-200 m and 10-25 m) revealed a collection rate of roughly 80%.
  • A proof-of-concept device can filter microplastics up to 300 m in diameter from water.
  • The tests removed more than 70% of small particles and 82% of large plastics.
  • To clean 1 L of water, the system costs 7 cents to run for 90 minutes.

Extra insights on the project

In preliminary studies using polystyrene, polyethylene, and polymethyl methacrylate microplastics, the researchers discovered that smaller (6- to 180-m-wide) particles behaved differently in the presence of acoustic forces than bigger (180- to 300-m-wide) particles.

Spiked into clear water, particles of both sizes arranged around the channel’s centre, escaping through the middle outlet, while clean water flowed out the surrounding outlets. However, if laundry detergent or fabric softener were added to the water, the larger particles concentrated to the sides and exited via the side outputs, while cleansed water exited through the centre outlet.

Based on these findings, the researchers set out to create a system that might capitalise on these varying movements.

Another technique introduced in past

Previously, Korean researchers devised a water-cleaning technology that can remove microplastics and other contaminants rapidly and effectively. The chemical that was employed is known as a covalent triazene framework (CTF). The substance was exceedingly porous and had a huge surface area; it had plenty of space inside for storing molecules that it captures.


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What is the best way to remove microplastics from water?

The best home filtering options for removing microplastics from drinking water include reverse osmosis, distillation, and ultrafiltration.

RO is primarily a five-stage process in which a membrane with tiny pores (0.001 microns) is used. This allows water to pass through while washing away minute pollutants such as microplastics.

Distillation involves boiling water, collecting steam, and cooling it back down to liquid form.

Water is filtered through a 0.2 micron membrane in ultrafiltration. Ultrafiltration, unlike RO systems, does not dispose of wastewater during the filtration process therefore is ineffective.

How do we reduce microplastics production and consumption?

The main cause of microplastic generation is weathering or degradation of products containing plastic and plastic already existing in micron sizes just like in beauty products. If we are cautious of the products we buy, and ditch the ones that contain plastic in them we can reduce contamination of plastic in our surroundings.

Clothes made from polyester or nylon, makeup products, plastic accumulation in landfills are few of the sources of microplastic production. See the detailed list here to know the hidden sources and avoid them.

As far as tips to avoid consumption is concerned, then we should know that plastic has now contaminated the entire ecosystem. Read here tips to know how to avoid microplastic consumption.

Why is it important to remove microplastics from water?

Microplastics removal from water sources is mandatory to avoid transferring it to the food chain. Fishes often confuse microplastic with food and consume them, thereby entering the foodchain and being consumed by all. Though  there has been no research made about serious impacts of plastic in the gut, but it’s better to take precautions than addressing new issues to health.


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