Scientists shine a light on what comes up when you flush

The world can now understand how flushing the toilet affects the environment according to recent study from CU Boulder.

A team of CU Boulder engineers conducted an experiment using bright green lasers and camera equipment to demonstrate how small water droplets that are undetectable to the human eye are quickly expelled into the air when a lidless, public restroom toilet is flushed.

It is the first study to directly view the ensuing aerosol plume and analyse the speed and distribution of particles within it; it is now published in Scientific Reports.

Customers using public restrooms could be exposed to these aerosolized particles, which are known to carry diseases. However, this clear illustration of potential disease exposure also offers a strategy to lessen it.

“It’s simple to deny something exists if you can’t see it. The study’s lead author and a professor of civil, environmental, and architectural engineering, John Crimaldi, claimed that after watching these movies, you won’t ever view a toilet flush in the same way again.

Our findings can significantly contribute to public health message by creating compelling visual representations of this process.

For more than 60 years, scientists have understood that when a toilet is flushed, both liquids and solids fall down as intended, but that minuscule, invisible particles are also released into the air.

However, until recently, no one knew what these plumes looked like or how the particles got there.

Previous studies have used scientific instruments to detect the presence of these airborne particles above flushed toilets and shown that larger ones can land on nearby surfaces.

In order to reduce exposure risk through ventilation and disinfection techniques, better toilet and flush design, or other exposure risk reduction measures, it is crucial to understand the trajectories and velocities of these particles, which can carry pathogens like E. coli, C. difficult, noroviruses, and adenoviruses.

The COVID-19 (SARS-COV-2) virus is prevalent in human faeces, however there is currently insufficient proof that it may effectively transmit by toilet aerosols.

 

A team of CU Boulder engineers ran an experiment to reveal how tiny water droplets, invisible to the naked eye, are rapidly ejected into the air when a lid-less, public restroom toilet is flushed

“People have known that toilets emit aerosols, but they haven’t been able to see them,” said Crimaldi. “We show that this thing is a much more energetic and rapidly spreading plume than even the people who knew about this understood.”

 

According to the study, these airborne particles travel swiftly, at a rate of 6.6 feet (2 meters) per second, and can be seen in the toilet bowl as high as 4.9 feet (1.5 meters) above the ground in just 8 seconds.

The smallest aerosols (particles less than 5 microns, or one millionth of a meter), on the other hand, can cling to surfaces for minutes or more whereas the largest droplets often settle onto surfaces in a matter of seconds.

The worries that restroom users have to deal with extend beyond just their own waste. Pathogens can survive in the bowl for dozens of flushes, according to numerous other research, raising the danger of exposure.

The worries that restroom users have to deal with extend beyond just their own waste. Pathogens can survive in the bowl for dozens of flushes, according to numerous other research, raising the danger of exposure.

The purpose of the toilet is to efficiently remove waste from the bowl, but Crimaldi noted that it also serves the opposite purpose by shooting a lot of garbage upwards.

“Our lab has developed an approach that serves as a basis for enhancing and reducing this issue.”

Not a waste of time

At the University of Colorado Boulder, Crimaldi is the director of the Ecological Fluid Dynamics Lab, which uses laser-based equipment, dyes, and enormous fluid tanks to examine everything from how chemicals travel in turbulent water to how aromas reach our nostrils.

It was a matter of convenience, curiosity, and circumstance that led to the idea of using the lab’s technology to monitor what transpires in the air when a toilet is flushed.

He set up and conducted the experiment over the course of a free week in June with the assistance of many graduate students from Crimaldi’s lab, colleague professors Karl Linden and Mark Hernandez of the Environmental Engineering Program, and others.

The study’s second author and research associate in Criminal’s lab, Aaron True, played a key role in conducting and compiling the laser-based data.

At the University of Colorado Boulder, Crimaldi is the director of the Ecological Fluid Dynamics Lab, which uses laser-based equipment, dyes, and enormous fluid tanks to examine everything from how chemicals travel in turbulent water to how aromas reach our nostrils.

They used two lasers, one of which shone on and above the toilet continuously, and the other of which fired quick bursts of light over the same area.

The pulsing laser could determine the speed and direction of the airborne particles, while the continuous laser showed where they were in space.

Two cameras simultaneously captured high-resolution photos.  The toilet itself was a lidless unit with a cylindrical flushing mechanism—whether manual or automatic—that sticks up from the back near the wall, known as a flushometer style valve.

These toilets are frequently found in public restrooms in North America. Only tap water was used to fill the fresh, new toilet.

They knew that this spur-of-the-moment experiment might be a waste of time, but instead, the research made a big splash.

“We had expected these aerosol particles would just sort of float up, but they came out like a rocket,” said Crimaldi. 

Although their direction of travel was uncertain, the energetic, flying water particles typically traveled upward and backwards towards the rear wall.

Additionally rising to the lab ceiling, the plume extended out from the wall and forward into the space since it had nowhere else to go.

There were no stalls or people moving around in the experimental setup, nor was there any solid waste or toilet paper in the bowl. All of these factors from real life could make the issue worse, according to Crimaldi.

They also used an optical particle counter, which counts and measures the airborne particles by sucking a sample of air in through a tiny tube and shining a light on it.

Knowing how many particles there are and what size they are was also crucial since smaller particles not only float in the air for longer periods of time, but they may also evade nose hairs and enter the lungs more deeply, making them more dangerous to human health.

Even though these findings may be unsettling, the study offers plumbing and public health specialists a repeatable means to evaluate enhanced plumbing designs, as well as disinfection and ventilation techniques, in order to lower the risk of exposure to pathogens in public restrooms.

They also used an optical particle counter, which counts and measures the airborne particles by sucking a sample of air in through a tiny tube and shining a light on it.

“None of those improvements can be done effectively without knowing how the aerosol plume develops and how it’s moving,” said Crimaldi. “Being able to see this invisible plume is a game-changer.”

Source: University of Colorado Boulder

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