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Spring 2020

Field Notes

A membrane made from agave cellulose nanofibers.
A membrane made from agave cellulose nanofibers. Photos courtesy of Hilary Urena-Saborio

Think of it as an environmental hangover.

Tequila production in the Mexican state of Jalisco yields vast quantities of agave bagasse biomass, which poses serious disposal problems. Most of this fibrous byproduct — which accounted for an estimated 40% of the 1,600 tons of agave processed in 2018 — ends up in clandestine dumps that contaminate the soil and degrade the fertility of surrounding farmland.

One potential solution is to put the waste to work. Researchers in the Department of Biological Systems Engineering have developed a novel application for the leftover biomass: They’ve transformed its fibers into highly effective water filtration membranes using cutting-edge nanotechnology.

The project built on groundwork laid by Belkis Sulbarán-Rangel, a professor at the University of Guadalajara. She had already extracted cellulose fibers from the agave bagasse biomass to create filter paper, but the paper disintegrated easily in water. While attending a conference on the UW–Madison campus, Sulbarán-Rangel consulted with members of the Gunasekaran Laboratory of Biosensing and Nanotechnology.

“We suggested that electrospinning would prove a much finer way to compose the filter,” says Sundaram Gunasekaran, professor and director of CALS Global, the college’s hub for international activities.

Clockwise from top left: Fifteen pounds of these agave piñas (hearts) produce one liter of tequila. A waste pile of agave bagasse after the piñas are crushed to release the juice for tequila production. A membrane made from agave cellulose nanofibers. A vial of unfiltered tap water stands next to a vial of water filtered through a membrane made from agave cellulose nanofibers and a biodegradable polymer.
Clockwise from top left: Fifteen pounds of these agave piñas (hearts) produce one liter of tequila. A waste pile of agave bagasse after the piñas are crushed to release the juice for tequila production. A membrane made from agave cellulose nanofibers. A vial of unfiltered tap water stands next to a vial of water filtered through a membrane made from agave cellulose nanofibers and a biodegradable polymer.

Electrospinning runs a charged polymer solution through a spinner under a high-voltage electric field. The solution coagulates to create ultrafine nanofiber filaments, which can be woven into a membrane. “The 3D structure of nanofibers generates a higher surface area, so you’re able to absorb a lot more particles than a regular sheet of paper would,” explains Hilary Urena-Saborio MS’19, a former graduate student in the Gunasekaran Lab.

The challenge for the agave project was to find just the right blend of polymers and agave cellulose nanofibers that, once formed into membranes, could not only withstand the forces of flowing water but also retain the highest percentage of contaminants.

Urena-Saborio and Hasbleidy Palacios Hinestroza, a visiting graduate student from the University of Guadalajara, zeroed in on three blends of cellulose nanofibers (CNF) and a biodegradable polymer known as polycaprolactone (PCL). They evaluated the blends — containing 20%, 40%, and 50% CNF, respectively — for viscosity (degree of stickiness), conductivity (how well it carries a charge), turbidity (clarity of water), and contaminant retention.

In the end, the 50-50 blend performed the best. It retained 75% of iron and 99% of chromium pollutants and left the water samples completely clear.

“The results show that CNF is a useful biowaste from tequila production that’s suitable as an eco-friendly filtration system for water purification,” says Urena-Saborio.

The membranes, which are 3 centimeters in diameter, would need to be scaled up individually or assembled into a matrix to be marketable. With this in mind, Gunasekaran sees commercial and environmental promise in their results.

“If this could establish a new market for the agave bagasse biomass, the growers would not dump it in the way they are now,” he says. “You’d immediately cut down on its pollution of waterways and other places.”

This article was posted in Bioenergy and Bioproducts, Economic and Community Development, Field Notes, Food Systems, Health and Wellness, Healthy Ecosystems, Spring 2020 and tagged , , , , , , , , , , .