Engineers less flush with success

By Nick Carne

Imagine if your poop didn’t stick. That’s stick.

Engineers from Penn State University in the US have developed a “robust bio-inspired, liquid, sludge- and bacteria-repellent coating” they say can essentially make a toilet self-cleaning.

Aside from the health and aesthetic benefits, it could greatly reduce the amount of water needed for each flush of a conventional toilet.

“Water scarcity threatens over half of the world’s population, yet over 141 billion litres of fresh water are used globally each day for toilet flushing,” Tak-Sing Wong, Jing Wang and colleagues write in the journal Nature Sustainability.

“This is nearly six times the daily water consumption of the population in Africa.” {%recommended 8814%}

And toilet bowls are not the only possible application, they say, for the liquid-entrenched smooth surface (LESS) coating developed in their Laboratory for Nature Inspired Engineering. 

It is, in fact, a two-step process. The first spray, created from molecularly grafted polymers, creates a smooth, liquid-repellent foundation, but when it dries it grows molecules that look like hairs, with a diameter of about 1,000,000 times thinner than a human’s.

The second spray infuses a thin layer of lubricant around those nanoscopic hairs to create an even more slippery surface.

“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],” Wang says.

A new coating would have to be applied to a conventional toilet after about 500 flushes, the authors note, but that would only take about five minutes.

They say their experiments also show the surface effectively repels bacteria, which spread disease and unpleasant smells – particularly valuable in waterless toilets that are used in developing countries and rural areas.

“The ability to prevent the fouling of faecal matter and bacteria will further reduce odour generation, which will make shared toilets more appealing to the public and could further promote safe and dignified sanitation,” they write.

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