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Slippery toilet coating eases turd passage to save water

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A spray-on coating that prevents faeces from sticking to toilet bowls has been developed by Penn State University engineers who say it can reduce the amount of water used while flushing.

There are few things in life less agreeable than a pre-soiled toilet bowl. But flushing typically uses six litres of water, amounting to more than 141 billion litres that is lost down the toilet every day. Reducing the amount of water used could make a significant contribution to relieving water scarcity, which affects hundreds of millions of people.

The team of engineers hope to halve water usage during flushing, by spraying toilet bowls with a coating which prevents poo from clinging to the surface: “Poop sticking to the toilet is not only unpleasant to users, but it also presents serious health concerns,” said Professor Tak-Sing Wong.

The spray is a liquid-entrenched smooth surface (LESS) coating which is applied in two steps. The first step involves coating the surface with molecularly-grafted polymers, which grows extremely thin (nanoscopic) hair-like molecules as it dries. In the second step, another spray is applied, infusing the hairs with a layer of lubricant. This renders the coating even more slippery.

“When we put that coating on a toilet in the lab and dump synthetic faecal matter on it, it just completely slides down and nothing sticks to [the toilet],” said Jing Wang, a doctoral student based in Wong’s laboratory, who co-developed the spray.

The coating could last for approximately 500 flushes before it needs to be reapplied. Unlike other liquid-infused slippery surfaces, which can take hours to cure, the LESS coating can be applied in less than five minutes.

According to the researchers, the coating repels liquid, sludge and bacteria (including those known to spread infectious diseases and unpleasant smells), effectively making a toilet “self-cleaning”. A toilet coated with the spray requires only a fraction of the water previous needed. The engineers hope that – if widely adopted just in the US – the coating could allow for water to be directed towards valuable causes, such as towards regions experiencing severe water shortages.

The spray could also be used in waterless toilets, which are commonly found in some regions of the world, and even render them more palatable for widespread use.

Professor Wong, Wang, and other collaborators have established a start-up, spotLESS materials, to bring the coating to market. Their research has been published in Nature Sustainability.

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