According to the United Nations, 2.1 billion people lack access to safely managed drinking water services and the majority live in developing nations. A process was developed that uses sand and plant materials readily available in many developing nations to create a cheap and effective water filtration medium called “f-sand.” F-sand uses proteins from the Moringa oleifera plant, a tree native to India that grows well in tropical and subtropical climates. The tree is cultivated for food and natural oils, and the seeds are already used for a type of rudimentary water purification; however, this traditional means of purification leaves behind high amounts of dissolved organic carbon (DOC) from the seeds, allowing bacteria to regrow after just 24 hours. This leaves only a short window in which the water is drinkable.
This method of water purification was combined with sand filtration methods common in developing areas. By extracting the seed proteins and adsorbing (adhering) them to the surface of silica particles — the principal component of sand — f-sand was created. It both kills microorganisms and reduces turbidity, adhering to particulate and organic matter. These undesirable contaminants and DOC can then be washed out, leaving the water clean for longer, and the f-sand ready for reuse.
A parameter of the f-sand manufacturing process — the concentration of seed proteins needed to create an effective product — was tested. The necessary concentration has a major impact on the amount of seeds required, which in turn has a direct effect on overall efficiency and cost-effectiveness. The key to achieving the proper concentration is ensuring that there are enough positively charged proteins to overcome the negative charge of the silica particles to which they are attached, creating a net positive charge. This positive charge is crucial to attract the negatively charged organic matter, particulates, and microbes contaminating the water.
Seed proteins were used to coagulate contaminants in the water prior to f-sand filtration. This relies on controlling the charge of the contaminants, which coagulate when they are neutralized. Applying too much protein can over-charge the contaminants and inhibit coagulation. This broad range of concentrations means that not only can water treatment processes be created at relatively low concentrations, thereby conserving materials, but that there is little risk of accidentally causing water contamination by overshooting the concentration. In areas where exact measurements may be difficult to make, this is crucial.
The f-sand manufacturing process displays a high degree of flexibility, as it is able to work at a range of water conditions and protein concentrations.