Mangrove trees are like no other — they can remove salt from seawater using a complex filtration system, which allows them to grow in places that other plants cannot.

Engineering professor Menachem Elimelech and his team have created a device that mimics the desalination capabilities of mangrove trees. The success of the device in purifying brackish water will pave the way for future studies on water transport in plants. In addition, the device shows promise for other environmental innovations.

“The principles established by the device could be used in a variety of applications, including dewatering of concentrated brines, environmental sensors and smart infrastructure,” Jay Werber GRD ’16 ’18, a project team member who performed preliminary experiments, wrote in an email.

Taking inspiration from the distinctive properties of the mangrove tree, the research team was able to model desalination using their own artificial device. Though the device does not visually resemble a mangrove tree, it has parts that function similarly to the mangrove’s. Specifically, the device’s “leaves” undergo capillary pumping, the “stem” supports stable water conduction and the “root” aids in water desalination.

The mangrove desalinates water by using evaporation at the leaves to generate a negative pressure, which is felt by the water that enters the stem. This poses a problem, namely, that at negative pressures, water is metastable — it is capable of becoming a gas. Mangroves have special features that allow them to efficiently transport water without it turning into a gas.

The team faced challenges in creating a device that transported water without forming air bubbles. Bubbles create unwanted air pockets and reduce the efficiency of water flow. The team ultimately decided to use glass frit material, which has similar properties to that of the mangrove, to suppress bubble formation.

“We fabricated and optimized at least three devices,” Wang said. “In our device, the leaf, stem and root touch tightly to reduce water transfer distance and bubble formation possibility.”

The research team reproduced the large, negative, capillary pressures using pores that are strongly attracted to water. According to Werber, the device can generate up to -300 atm of negative pressure, the largest in an engineered device to date.

The Yale group also looked to confirm whether mangroves use the “cohesion-tension theory” to transport water.

“[The device] not only opens up new possibilities for passively driven engineered separations, but also provides experimental validation of the cohesion-tension theory for the generation and utilization of negative pressures for water transport and desalination in plants,” Yunkun Wang, visiting professor at the Elimelech Lab and lead author of the study, wrote in an email to the News.

According to Wang, the technology used in the device can be used in stormwater management and water desalination.

Studies indicate that, pound for pound, mangrove forests can sequester four times more carbon dioxide than rainforests can.

Katherine Du | katherine.du@yale.edu

KATHERINE DU