Water is essential for life, but nearly 2.1 billion people — over 28 percent of the world population — lack access to safe drinking water, the United Nations warns.

This crisis alone causes more deaths per year than violence or war, and is so drastic that every minute a child dies of water-related disease, resulting in an urgent need for action.

Luckily, biomedical engineers and chemical engineers from Carnegie Mellon University (CMU) have a solution.

Their method lies in the properties of a seed.

They use sand and plant materials found readily available in many developing nations — an idea conceived by Stephanie Velegol, a former CMU doctoral student and now a professor of chemical engineering at Penn State University, which she called “f-sand” — to develop a cheap and effective water filtration medium.

The research is available in the journal ACS Langmuir.

What is “f-sand”?

F-sand uses seed proteins from the Moringa oleifera plant, a tree native to India that can grow well in tropical and subtropical climates. Typically, the tree is cultivated for its commercially valuable food and oils, and the seeds have been used for a type of low-grade water purification process.

However, this rudimentary purification leaves behind high amounts of dissolved organic carbon from the seeds, which can allow bacteria to regrow in as little as 24 hours — leaving a drastically short time-frame in which the water is drinkable.

To circumvent this issue, Velego had the idea of combining this method with sand filtration techniques common in developing areas.

This is because f-sand is completely based on the idea that opposite electrical charges attract, explained Bob Tilton, the Chevron Professor of Chemical Engineering and Biomedical Engineering at CMU.

“Sand is mostly negatively charged. The proteins from the Moringa oleifera seeds are positively charged, and most of the suspended contaminants (suspended clay or other mineral particles, bacteria, decomposing organic material naturally found in the environment) that should be removed from water to make it potable are negatively charged,” he said.

How it works

To prepare f-sand, Tilton explained, the water-soluble proteins are first extracted from the seeds by crushing them and soaking them in water. The resulting solution is then poured into a very thick, wet mixture of sand and water called a slurry.

At this time, the negative sand charge attracts to the positive protein charge, causing the proteins to stick to the sand, and subsequently, create “f-sand.” The excess water can then be drained out and the f-sand can be poured into a column.

The column can be made out of materials, such as a PVC pipe with mesh at the bottom, or even a piece of bamboo, said Tilton.

Then, to use the f-sand, one would simply pour water through the column, and the negatively charged contaminants would stick to the positively charged proteins on the sand grains, creating a simple and resourceful filtration system.

“Stephanie’s idea was that if you could confine the proteins that agglomerate the contaminants to sand (knowing about the charge of sand and the proteins) and then rinse the sand, you could dramatically decrease the residual organic compounds to prevent microbial re-growth,” said Tilton.

Investigating fatty acids

Though the basic process was proven to be effective, the researchers still had many questions surrounding f-sand’s creation and use — questions that Tilton and Todd Przybycien, a professor of chemical engineering at CMU, sought to answer.

For one, the engineers wanted to know if the fatty acids and oils — the commercially valuable aspects of Moringa oleifera — played a role in the protein absorption process.

Overall, they found that removing the fatty acids had little effect on the protein absorption, which means people in the region can remove and sell the valuable oils while still being able to extract the proteins for water filtration.

Concentration levels

Additionally, the researchers wanted to understand what the necessary concentration of seed proteins was to create an effective product.

In other words, the researchers needed to make sure that there were enough positively charged proteins to overcome the negative charge of the sand particles, in order to create a net positive charge.

This is crucial for f-sand to work.

The team used a technique called a “streaming potential measurement” to determine how the charge on the sand depended on the amount of protein on the surface.

In all, the researchers found that only very small concentrations were needed to switch the charge from negative to positive, which will allow people to conserve the plant materials.

Additionally, they measured a variety of water contents to determine if the filtration technique could display a high degree of flexibility.

“The amount of protein that adsorbs to a surface is directly controlled by the concentration of protein in the ‘bulk’ water that bathes the surface. We measured the relationship between the amount adsorbed and the bulk water concentration, for different water compositions that represent soft, moderately hard and hard water to try to capture the wide variation in natural water contents,” said Tilton.

Tilton and Przybycien found that proteins were able to absorb well to sand in both soft and hard water conditions, illustrating the potential for the filtration process to be used across a wide array of regions.

The next step

So far, the research has been tested by Velegol in Rwanda, and Tilton’s team is currently running tests to determine the lowest protein concentrations that would work with f-sand, as well as the limits of f-sand’s performance.

“We are currently testing how small alterations in sand coverage by protein alter the performance of f-sand columns to clarify model turbid water — to really see how robust the process is if people were to operate at the very lowest protein concentrations,” said Tilton. “We are also testing to find the limits of f-sand performance — for example, to see if the presence of high concentrations of organic matter in the source water could overwhelm the f-sand and hinder its ability to remove suspended solids.”

Though they have not done an economic analysis, the researchers believe that the abundance of Moringa will make f-sand quite affordable.

“Moringa grows well in tropical regions with sandy soil. So, wherever one is likely to grow the tree, there will also be plenty of sand available (and the sand can be re-used by washing it off with a salt solution),” said Tilton. “Moringa is also a very fast growing tree. A good thing about the fact that very low concentrations of protein are enough to switch the sand charge from negative to positive is that in principle it can make the seed resource go further.”

Additionally, Tilton explained, f-sand will be easily adapted by local users, since the technique requires few tools and fairly simple work.

“Systems could be set up to work at a very localized level, probably even at the individual household level,” he said.

The research puts this novel technology one step closer to the field, as a relatively low-cost technique that could bring clean water to communities across the world.