2/5/2024
It is estimated that by 2025, half of the world will face severe water scarcity, meaning nearly 4 billion people will be left without a safe supply of water. While it may be hard to imagine such a reality in the United States, the fact of the matter is that it is already happening. From the Flint Water Crisis to severe droughts in California and Minnesota, water scarcity in the U.S. is well on its way. As engineers, it is our responsibility to find ways to avert crises such as this – a responsibility that researchers are taking very seriously at the University of Texas.
Less than a month ago, lead researcher Chuxin Lei and his team created a cheap and easy-to-use water filtration system. The device is like a giant syringe with a sponge near the lower half that decontaminates the water. This “sponge” is a bio-based nanofiber hydrogel filter (BNHF). It was especially constructed to filter out suspended solids (SS) which are ultrafine water contaminants like bacteria or microplastics, which most filters cannot currently do. This is because most water filters aim to block particles linearly. Most commercial water filters can be visualized much like a net trampoline tower in a trampoline park. The net is a grid of fibers that have uniform, square gaps in the middle. While it may be difficult for an adult to slip through the gaps of the tower, a child can slip through very easily. Which, unfortunately, means that contaminants are passing through the filter.
In comparison, the BNHF uses crosslinked nanofibers. Going back to the net tower analogy, the BNHF would use a series of criss-crossed fibers and safety nets rather than only using a grid of squares, producing a web-like surface. The gaps are so minuscule and tightly linked that even if a child managed to slip through, they would eventually get caught in a lower level. This is exactly what the BNHF does. It uses a microporous membrane as a base which is then injected with aqueous nanofibrillated cellulose (NFC) to produce a fine mesh filter, purging even the smallest particles.
What makes the BNHF filtration system so miraculous is its simplicity. The whole contraption is only four pieces: a syringe, a microporous membrane, the membrane support (which looks like two small suction cups), and the aqueous NFC. The simple design means once it is set up, all that needs to be done is to have water injected water into it. As long as you can use a syringe, you can use the BNHF system. It’s so small it could fit in a small handbag, which means it can easily be taken anywhere. Despite its small size, the BNHF filters water rapidly. It’s also sustainable. While experimenters found that the filter could be reused up to 30 times, once it’s no longer functional it can be discarded in soil since NFC is a completely biodegradable substance. On top of being eco-friendly, NFC is also very cheap to produce. This makes the BNHF filter affordable and accessible to those who need it.
A normal BNHF can filter about 10 mL of water. To test its practicality, researchers put melted snow, dirty river water, soil-polluted water, and nanoplastic-contaminated water, respectively, through the filter. In each case, the filter was able to remove 100 percent of the contaminants. Researchers then upscaled the filter so that it could collect 1.5 mL of water, and obtained similar results. After conducting a water quality test, they found that the water produced met the standard for drinking water quality. The only real limitation of the BNHF is the size of microparticles it can capture. At the moment, it is unable to filter particles smaller than ten nanometers. To put that into perspective, most water filters can only filter particles 1 micrometer or larger. That means that the BNHF can block particles 1000 times smaller than the average water filter. Even so, the University of Texas engineers are working to create a finer filter. Until then, they have provided the world with a pragmatic approach to accessing safe water.