New self-cleaning coating reduces water needed to flush a toilet

A novel bacteria-repellent coating could dramatically reduce the amount of water needed to flush a toilet, which usually requires six litres, scientists say.

The research was published in the journal Nature Sustainability on the eve of the World Toilet Day being observed on Tuesday. The researchers noted that while millions of global citizens experience water scarcity, every day, more than 141 billion litres of water are used solely to flush toilets.

"Our team has developed a robust bio-inspired, liquid, sludge- and bacteria-repellent coating that can essentially make a toilet self-cleaning," Tak-Sing Wong, a professor at Pennsylvania State University in the US, said in a statement. The liquid-entrenched smooth surface (LESS) coating is a two-step spray that, among other applications, can be applied to a ceramic toilet bowl, the researchers said.

The first spray, created from molecularly grafted polymers, is the initial step in building an extremely smooth and liquid-repellent foundation, they said. "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 said in a statement. While this first application creates an extremely smooth surface, the second spray infuses a thin layer of lubricant around those nanoscopic "hairs" to create a super-slippery surface, the researchers explained. "When we put that coating on a toilet in the lab and dump synthetic faecal matter on it, it (the synthetic fecal matter) just completely slides down and nothing sticks to the toilet," Wang said.

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 previously needed. The researchers also believe that the coating could last for about 500 flushes in a conventional toilet before a reapplication of the lubricant layer is needed.

While other liquid-infused slippery surfaces can take hours to cure, the two-step LESS coating takes no more than five minutes. The researcher's experiments also found the surface effectively repelled bacteria, particularly the ones that spread infectious diseases and unpleasant odours. The technology could be used within waterless toilets, which are used extensively around the world, the researchers said.

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