Tag Archives: filtration

We could blast microplastics out of water using loudspeakers, although the tech is still young

Sound can help us deal with the growing issue of microplastics plaguing the world’s oceans, according to new research.

Image via Pixabay.

Microplastics are building up in all layers of the environment, from soils to waterways, even in the atmosphere. Such particles are produced directly by cosmetics, clothing, or industrial processes, or indirectly through the breakdown of larger pieces of plastic.

They’re becoming a genuine environmental concern risking the health of both humans and wildlife. Considerable effort has been put into developing efficient ways of disposing of microplastics, with varying success. Now, new research from the Institut Teknologi Sepuluh Nopember in Surabaya, Indonesia offers an unusual solution to the problem — filtering them out of the water using sound.

Speakers to the rescue

The approach involves using speakers to generate “bulk acoustic waves” (sound waves that propagate throughout the volume of a substance) in order to force microplastic particles in water to separate from the liquid. This allows for the quick and easy removal of the particles through mechanical means, offering a clean and quick method to scrub waters of microplastics.

During lab testing of their technique, the researchers used two speakers to generate acoustic waves through a sample of water laden with microplastic particles that was circulated through a tube. The force of these waves (sounds propagate through physical motions of a material’s particles) created pressure inside the tube, forcing the plastic microparticles to move towards the center of the tube. This tube eventually split into three channels, with the middle one removing the plastic while the other two carried the cleaner water away.

During the testing, the team’s device scrubbed around 150 liters of polluted water an hour. They tested three types of microplastic particles in pure water and seawater. The effectiveness of the rig depended mostly on the type of water that was flowing through it but also varied with the type of plastic it contained. However, the lowest efficiency ratings of the device were slightly above 56% in pure water and 58% in seawater across all types of microplastics used in the trial.

The team explains that this was only a proof-of-concept run. They’re confident that with further tweaking to the frequency of acoustic waves they generate, of the distance between the speakers and the tube, and the water flow through the tube, higher efficiencies can be attained. How much plastic can be removed throughout a cycle of the device directly depends on how much pressure can be generated in the water using the sound waves, and all those elements would affect this parameter.

One potential issue with the technology that may severely limit its applicability in the wild is that many marine species are highly sensitive to sounds in the audible range of frequency — the same range over which the team blasts their speakers. The authors are hard at work finding potential solutions to this problem. In case this can’t be addressed, the technology still holds promise in scrubbing water before it is dumped in waterways. While this won’t help clean the plastic already floating around the oceans, it can at least limit the influx of new microplastics.

“We believe further development is necessary to improve the cleaning rate, the efficiency, and particularly the safety of marine life,” said Dhany Arifianto, Chair of Vibration and Acoustics at Institut Teknologi Sepuluh Nopember Surabaya, lead researcher on the project.

The findings will be presented at the 181st Meeting of the Acoustical Society of America in Seattle, Washington on Dec. 1st.

Nonthermal reactor.

Cold plasma reactor neutralizes 99.9% of airborne viruses in new study

New research is looking into how we can better protect sterile environments from airborne viruses.

Nonthermal reactor.

Professor Herek Clack (left) and members of his team set up a lab-scale non-thermal plasma device that has previously been proven to achieve greater than 99% inactivation of an airborne viral surrogate, MS2 phage, a virus that infects E.coli bacteria at the Barton Farms family pig farm in Homer, MI.
Image credits Robert Coelius / Michigan Engineering

Nonthermal plasmas — ionized, charged particles formed around electrical discharges such as sparks — are very, very good at rendering airborne viruses harmless, a new study reports. This approach could help us better keep environments such as surgery rooms clean of pathogens, the authors explain, and might even render the surgical mask obsolete.

Sparkly fresh

“The most difficult disease transmission route to guard against is airborne because we have relatively little to protect us when we breathe,” said paper co-author Herek Clack, a research associate professor of civil and environmental engineering at the University of Michigan.

Exposure to nonthermal plasmas, however, could be just the guard we need. In their study, the team crafted a nonthermal plasma reactor which was able to remove 99.9% of a test virus the researchers pumped through. Best of all, the whole process only took a fraction of a second to complete. The vast majority of the virus sample was rendered harmless due to inactivation, the team notes, with a sliver of the bugs getting scrubbed out of the airstream thanks to good old fashioned filtration.

The reactor used in this study looks suspiciously like a piece of pipe because it is. The real magic happens inside. The team packed borosilicate glass into a cylindrical-shaped bed, which they placed inside the reactor. Then, they pumped a model virus (one harmless to humans) inside the rig, forcing the virus to pass through the spaces between the beads. Then, they started the reactor.

“In those void spaces, you’re initiating sparks,” Clack said. “By passing through the packed bed, pathogens in the air stream are oxidized by unstable atoms called radicals.”

“What’s left is a virus that has diminished ability to infect cells.”

The team tracked the amount of viral genome present in the air coming out of the reactor to gauge how it went about neutralizing the pathogens. These measurements revealed that more than 99% of the air sterilizing effect was due to inactivating the virus that was present, with the remainder of the effect due to filtering the virus from the air stream.

This two pronged-attack that combines filtration with inactivation is likely much more efficient than currently-available air sterilization techniques, the team reports, such as the use of filtration or ultraviolet light. That’s because these other approaches rely on a single sterilization method masks, for example, only employ filtration. Even the use of ultraviolet irradiation falls short, they explain, as it can’t sterilize a volume of air as quickly, thoroughly, or compactly as the nonthermal plasma reactor.

“The results tell us that nonthermal plasma treatment is very effective at inactivating airborne viruses,” said Krista Wigginton, assistant professor of civil and environmental engineering, and a co-author of the study. “There are limited technologies for air disinfection, so this is an important finding.”

The team has started a second phase of testing its reactor. They installed it to the ventilation air streams at a livestock farm near Ann Arbor, where they hope the nonthermal plasma will prove its worth in stomping out contagious livestock diseases such as avian influenza. Fingers crossed!

The paper, “Inactivation of airborne viruses using a packed bed non-thermal plasma reactor,” has been published in the Journal of Physics D: Applied Physics.

Credit: MaxPexel.

Unlike your vacuum, the manta ray never clogs — and it might inspire microplastic filters

Credit: MaxPexel.

Credit: MaxPexel.

The devilish-looking manta ray spends most of its day on the sea floor, foraging for plankton with its mouth wide open. They can go for up to ten minutes without closing their mouths, and even then just for a brief moment. You’d think that this car-sized filter feeder would get clogged, but judging from countless observations the manta ray doesn’t seem to have any problems. It doesn’t even cough as some other sieving creatures do in order to clear debris from their filters.

Writing in the journal Science Advances, researchers at the California State University, Fullerton, describe how the remarkable animal pulls off this feat. It seems like the fish uses a previously unknown filtration system that allows food particles and other debris to glide over its straining system rather than through it.

Manta ray's gill rakers. Credit: Misty Paig-Tran.

Manta ray’s gill rakers. Credit: Misty Paig-Tran.

The manta ray’s mouth is lined with V-shaped rods called gill arches that feature comb-like teeth protruding both forward and backward. Each tooth is lined with small flaps that overlap and when water hits each flap, it forms swirling vortices. This way, particles of food don’t get sucked down through crevices, but instead get pushed up, concentrating in the ray’s mouth. The particles never really get into the filter, which is kept clean.

The researchers showed how the ray’s sieving works both theoretically with models of the Giant oceanic manta ray (Manta birostris) and experimentally with washing colored dyes.

Remarkably, the fish evolved this self-cleaning filtration that extracts solid food from liquid currents while cleaning the sieve in the process. No other animal is known to feed in this way, although the researchers suspect that other creatures may employ the same mechanism. Some whales or the Hawaiian bobtail squid are listed as possible candidates, which other studies might confirm that they use the same feeding system.

By understanding how the ray’s filtration system works, scientists may one day design bio-inspired technologies that never clog. For instance, the authors hope to build a system that removes algae from freshwater and, ultimately, they would like to sieve microplastics from wastewater directly at processing plants.

Unfortunately, manta rays are now listed as vulnerable to extinction due to a sudden spike in fishing. Historically, humans were never interested in manta rays because their meat was never appealing to consumers. However, their gill rakers are in demand on Asian markets, where they’re grounded into a powder which supposedly has detox properties. There is no evidence that the product has any cleansing effects.