Ultrasound to remove plastic particles from water

Every year, a huge amount of plastic waste is thrown into the environment. This plastic tends to break down into smaller pieces until particles of sizes less than 5 millimeters, which are known as microplastics, arise. These microplastics can be in the environment for a long time. Their presence in water is especially worrying, since it can enter the food chain from there. Concern is growing about the effects of microplastics on human health.

Filtration is the most common technique for removing these materials from water. However, this method can be expensive at a high price, as it requires periodic cleaning of the filters, which clog very easily.

Another option is to focus on water by acoustic forces on plastic particles, specifically sound waves that transfer energy to nearby solid particles, causing some of them to vibrate and move. The end result is that the particles are grouped into balls, which makes it much easier to remove them from the water. This physical phenomenon has already been used in other fields, for example, to separate solid biological particles from liquids, such as red blood cells from blood plasma.

A team led by Menake Piyasena and Nelum Perera, from the New Mexico Institute of Mining and Technology (New Mexico Tech) in the United States, has devised a system that uses ultrasound in water to group microplastics present and facilitate their extraction.

Microplastics naturally disperse in the water (left), but after the sound waves are reduced, the particles are forced into the sides of the tube (right), so they can be removed more easily. (Image: Menake Piyasena)

After many experiments and design modifications, the researchers created a very promising prototype that cleans water at high speed. The purified water passes through the pipes. In the first section, ultrasound allows the removal of microplastics smaller than 180 micrometers in size. Then the water passes to the second section, in which ultrasound acts on the remaining microplastics.

In tests carried out so far, the first section was able to extract more than 70 percent of microplastics, while the second was able to extract more than 82 percent.

This system for purifying water from microplastics was officially presented at the meeting of the ACS (American Chemical Society). (Source: NCYT from Amazing)