Self-Cleaning Coatings and Lubricants to Decrease Water Consumption in Toilets

Tot toilet
Toto toilet demonstration, CES 2020

Decreasing water consumption is a key theme in today’s world, as we deal with the ever-growing concern of water scarcity. Water scarcity is the inability of freshwater sources to meet the water demand of the planet and its inhabitants. Since the last century, water use has grown at more than twice the rate of population growth.

Every continent is affected by water scarcity. Approximately two-thirds of the world’s population (around 4 billion people) experience severe water scarcity for at least one month per year. Almost one-half million people deal with severe water scarcity all year long.

Approximately 70 percent of Earth’s surface is covered with water. However, only 3 percent of that water is fresh water and two-thirds of all fresh water is not available for use, often because it is frozen in glaciers.

While water scarcity is clearly a major global concern, more than 141 billion liters of water are used daily around the world to flush toilets. That means that the amount of water flushed down toilets each day is almost six times greater than the daily water consumption of the entire population of Africa.

Clearly, reducing the sheer volume of water flushed down toilets would be an excellent step towards helping ease the world’s water scarcity concerns. Tak-Sing Wong, a Wormley Early Career Professor of Engineering and Associate Professor of Mechanical Engineering and Biomedical Engineering at Penn State University explains that his team has developed a coating for toilets that basically turns any toilet into a self-cleaning model.

Researchers from the Wong Laboratory for Nature Inspired Engineering have developed a liquid-entrenched smooth surface (LESS) coating in a spray form. Applying the spray to the inside surface of toilets reduces the amount of water required to flush the conventional toilet.

The conventional toilet requires a large volume of water (typically 6 liters) for the flushing process due to the sticky nature of human feces, which tends to stick to the side of the toilet bowl. The LESS coating makes the toilet bowl more liquid-repellent and therefore human feces does not adhere to the sides and less water is required to flush the waste down the toilet.

Applying the LESS coating is a simple two-step process. The first spray is made up of molecularly grafted polymers. When it dries, the spray grows molecules that look like tiny microscopic hairs, which are one million times thinner than a human’s hair, creating a smooth surface. The second spray inserts a slight layer of lubricant around the tiny hairs, creating an extremely slippery surface. The two-step process requires less than five minutes to complete.

After using the spray, toilets require only a fraction of the amount of water previously required to flush waste. Researchers predict that the spray will last for up to 500 flushes before it needs to be reapplied to the conventional toilet. The coated surface also repels bacteria, especially those that spread disagreeable odors or diseases.

The researchers believe that this new coating is an important step towards lessening water usage, thus easing the burden on our limited fresh water supply. As a result of the discovery, Wong, Wang, Birgitt Boschitsch, and Nan Sun have begun their own start-up venture, called spotLESS Materials. The company already has the spray on the market with support from the National Science Foundation, Ben Franklin Technology Partners’ TechCelerator, the Office of Naval Research, the Rice Business Plan Competition, and the Department of Energy.

Further details regarding the group’s research and findings can be found in the article “Viscoelastic Sold-Repellent Coatings for Extreme Water Saving and Global Sanitation https://www.nature.com/articles/s41893-019-0421-0.

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