Scientists from Penn State University have developed a spray-on coating that is super-slippery (more slippery than Teflon) for the inside of a toilet bowl, so poo will slide right down, without leaving a trace behind. Testing revealed that the coating effectively reduced the adhesion of even the most tenacious feces by up to 90%. Meaning, less water is required to flush it away and leave the toilet bowl clean, so the invention helps to conserve water.
One of the scientists, Tak-Sing Wong, told The Guardian:
I was very happy to see how easily the fecal matter slid off our coated surface.
Wong started the research to find a solution to dirty toilets back in 2015. Cranfield University researchers contacted him for assistance in designing a toilet for the developing world. They were having issues with the odorous waste buildup on the surface of the toilet bowl due to a lack of sufficient water for flushing. Wong said they had contacted his research group because they were known for developing highly slippery coatings that could repel sticky substances.
They took on the challenge immediately and spent the next few years creating a coating they call a “liquid entrenched smooth surface.” It consists of two parts: a base layer of protruding “nano-hairs” that binds to the toilet bowl and a top layer of silicone oil. The nano-hairs are each a billion times thinner than a strand of human hair, but all of them together securely hold the silicone oil in place. The two layers are put on one after the next, and the entire procedure of coating the toilet bowl takes less than five minutes.
Mark Miodownik, professor of materials and society at UCL, said:
People will be familiar with the effectiveness of non-stick frying in their lives, and a similar approach to solving the problem of stickiness is behind this ingenious piece of materials science. This time the problem is not eggs sticking to a cooking pan, but poo sticking to the toilet pan.
They tested the coating with synthetic and real human feces. They dropped the samples from a distance of 40cm down onto 45-degree angled test plates. Then, they measured how much water was required to dislodge the feces entirely from the surface. The results revealed it took 90% less water than feces dropped onto glass sheets and toilets made of Teflon, ceramic, or silicone. The research has been published in the journal Nature Sustainability.
Wong said:
More than 141bn liters of fresh water is used to flush toilets each day, or nearly six times the daily water consumption of Africa. With millions around the world facing severe water scarcity, I hope that reducing the amount of water used for flushing could help to alleviate the problem.
As a bonus, the scientists’ coating was found to be better at preventing bacteria from urine, feces, or rainwater from accumulating and growing in the toilet. The coating was able to withstand 500 flushes but only 50 “urination cycles.” Therefore, it would have to be reapplied every 50 flushes.
There is one concern, however, is the coating safe for the environment? Miodownik said:
As this paper shows, such toilets would need less water per flush to clean them and also increase toilet hygiene. My one worry, which I’m sure the scientists will address as they do further work, is what happens to the coating when it does wear away through use – how would chemicals involved affect the environment if adopted globally?
More research is needed to test the ecological safety of the coating since part of it does release into the water after every flush. If they find it is safe, then the coating could be used in toilets where water is scarce or even where there is no water for flushing to provide a more hygienic and less odorous experience.
