Coating Creates Self-Cleaning Toilets That Use a Fraction of the Water

Liquid-entrenched smooth surface (LESS) coating repels bacteria that stink and infect

Published: Wednesday, December 18, 2019 - 13:00

Every day, more than 141 billion liters of water are used just to flush toilets. The new method dramatically reduces the amount of water needed to flush a conventional toilet, which usually requires six liters.

“Our team has developed a robust bio-inspired, liquid, sludge-, and bacteria-repellent coating that can essentially make a toilet self-cleaning,” says Tak-Sing Wong, professor of engineering and associate professor of mechanical engineering and biomedical engineering at Penn State.

Testing the self-cleaning toilets

Jing Wang, a doctoral graduate from Wong’s lab, co-developed the liquid-entrenched smooth surface (LESS) coating, which is a two-step spray that, among other applications, can be applied to a ceramic toilet bowl. The first spray, created from molecularly grafted polymers, is the initial step in building an extremely smooth and liquid-repellent foundation.

“When it dries, the first spray grows molecules that look like little hairs, with a diameter of about 1,000,000 times thinner than a human’s,” Wang says.

While this first application creates an extremely smooth surface as is, the second spray infuses a thin layer of lubricant around those nanoscopic “hairs” to create a super-slippery surface.

“When we put that coating on a toilet in the lab and dump synthetic fecal matter on it, it (the synthetic fecal matter) just completely slides down and nothing sticks to it (the toilet),” Wang says.

With this novel slippery surface, the toilets can effectively clean residue from inside the bowl and dispose of the waste with only a fraction of the water. The researchers also predict the coating could last for about 500 flushes in a conventional toilet before a reapplication of the lubricant layer is necessary.

While other liquid-infused slippery surfaces can take hours to cure, the LESS two-step coating takes less than five minutes. The researcher’s experiments also found the surface effectively repelled bacteria, particularly ones that spread infectious diseases and unpleasant odors.

Saving water

If it were widely adopted in the United States, it could direct critical resources toward other important activities, to drought-stricken areas or to regions experiencing chronic water scarcity, say the researchers.

Driven by these humanitarian solutions, the researchers also hope their work can make an impact in the developing world. The technology could work in waterless toilets, which are used extensively around the world.

“Poop sticking to the toilet is not only unpleasant to users, but it also presents serious health concerns,” Wong says.

However, if a waterless toilet or urinal used the LESS coating, the team predicts these types of fixtures would be more appealing and safer for widespread use.

To address these issues in both the United States and around the world, Wong and his collaborators began a start-up venture.

With support from the Ben Franklin Technology Partners’ TechCelerator, the National Science Foundation, the Department of Energy, the Office of Naval Research, the Rice Business Plan Competition and Y-Combinator, the researchers’ company, spotLESS Materials, is bringing the LESS coating to market.

Looking forward, the team hopes spotLESS Materials will play a role in sustaining the world’s water resources and continue expanding the reach of their technology.

A paper on the work appears in Nature Sustainability. Additional coauthors are from Penn State and the Centre for Competitive Creative Design of Cranfield University, UK.

Support for the work came from National Science Foundation; the Wormley Family Early Career Professorship; and the Humanitarian Materials Initiative Award, which Covestro and the Materials Research Institute fund.

Source: Penn State

Original Study DOI: 10.1038/s41893-019-0421-0                                                                     

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