A group of high school students have come up with a clever solution to the issue of lead contamination in drinking water by creating an inexpensive attachment that removes the toxic metal.
Rebecca Bushway is a science teacher at Barrie Middle and Upper School in the US state of Maryland. While teaching an upper-level high school chemistry class she asked if there was a little filter—similar to the ones that are made for camping to purify water—that they could make from inexpensive components to easily remove lead.
Lead is a major issue for millions of homes across the US, especially those in low-income communities, who still receive drinking water through pipes containing lead. If the chemistry of the water is not ideal, or it flows quickly because of high demand, then pipes can corrode. When the corroding material contains lead, the toxic metal dissolves or flakes off into the water, contaminating it with a dark discoloration and sometimes visible particles.
Although various lead filtration systems exist, their high cost and large size can be a barrier. In addition, few of them provide any indication that they should be changed, and none indicate that the water could pose an immediate health risk.
The solution created by the students aims to tackle this issue as their design contains a cartridge made with biodegradable plastic, which indicates when it needs replacing by turning the tap water yellow.
"There's really no safe level of lead in drinking water, so wouldn't it be nice to have a water filter that could tell you that your water is contaminated, well before it turns brown because of lead?"
The students decided to try and come up with a low cost, sustainable solution, and in 2020, when COVID-19 restrictions kept them out of the classroom, they began to meet virtually to discuss designs.
In spring 2021, when they returned to the classroom, they 3D printed the attachment and a three-inch-tall filter housing, using a biodegradable plastic. Their final step was to fill the cartridges with a mixture of calcium phosphate and potassium iodide powder.
"Calcium phosphate first binds with dissolved lead in water to form lead phosphate and free calcium. The calcium, which is harmless, ends up in the water, and the lead phosphate stays in the filter," explains Bushway.
Lead phosphate, which is an inert solid, is trapped inside the filter by a nylon screen on the bottom of the unit. Once the reaction capacity of the calcium phosphate is reached, dissolved lead reacts with potassium iodide, which turns the water yellow - indicating lead is present.
Crafting the water filtration system proved complex as calcium phosphate tends to clump up, causing the reaction rate between it and lead to go down as the surface area decreases. So, the teams lead student engineer incorporated hexagonal bevels inside the filter.
"Ultimately, this experience has shown students that they can make a difference to somebody, and there are problems that they can fix with science."
The projects findings were presented by Bushway at the spring meeting of the American Chemical Society (ACS) in March 2022.
The team's goal is to make and sell their filters for less than $1 each, which Bushway thinks they're on their way to doing. Because the housings use biodegradable plastic, the cost could be slightly higher, but the material would help reduce the overall environmental impact of the filter.
The process of developing the filter has been very fulfilling, says Bushway. "Ultimately, this experience has shown students that they can make a difference to somebody, and there are problems that they can fix with science," she says.