Pilot Study Uses Recycled Glass to Grow Salsa Ingredients, Protect Coastlines

Researchers at the University of Texas Rio Grande
Valley are conducting experiments to see if glass waste
can replace a depleting natural resource and support sustainable agriculture.

In a recent study, the team reports that growing certain food crops in recycled
glass from discarded, pulverized bottles — such as those from beer or soda. The
pilot study found that partially substituting soil in a planter with
recycled-glass fragments can speed up plant development and reduces unwanted
fungal growth.

The researchers present their results this week at the Fall 2024 meeting of the
American Chemical Society (ACS), Aug. 18-22 — which
features about 10,000 presentations on a range of science topics.

When nanomaterial scientist Julie
Vanegas joined the
faculty at the University of Texas Rio Grande Valley, she was paired with
faculty mentor Teresa Patricia Feria
Arroyo — an
ecologist who works on problems related to food security and sustainability.
During their early conversations, Vanegas mentioned that she’d been assessing
recycled-glass particles for use in coastal-restoration projects — such as
one studied by Louisiana’s Tulane
University
in 2022 — and Feria wondered if glass could also be used for growing produce.

To answer the question, the two developed experiments for growing popular food
ingredients that mature quickly and can be cultivated in container and backyard
gardens: They chose cilantro, bell pepper and jalapeño — key
ingredients in pico de gallo.

“We’re trying to reduce landfill waste at the same time as growing edible
vegetables,” says Andrea
Quezada, a chemistry
graduate student in the Nanoworld
Vanegas lab who is presenting the team’s
research at the Fall meeting. “If this is viable, then we might be able to
introduce glass-based soils into agricultural practices for people here in the
Rio Grande Valley and across the country.”

Image credit: University of Texas Rio Grande
Valley

As ACS explains in this video,
putting recycled glass to use as a sustainable soil amendment could help address
three problems:

• glass waste in landfills — according to the
  EPA,
  we only recycle about 31 percent of glass in the US; non-recycled glass
  represents about 5 percent (7.6 million tons) of the waste in US landfills
  each year.

• soil erosion — average soil erosion
  rates
  by wind and water in the US are roughly 4.63 tons per acre per year, with
  total soil loss of 1.70 billion tons; the UDSA
  estimates
  the US loses about $44 billion each year from soil erosion.

• sand shortage — around the world, billions of tons of sand are extracted
  per year for various uses; according to
  UNEP,
  it drives erosion, flooding, the salination of aquifers and the collapse of
  coastal defenses.

The researchers hope that the addition of glass to soil at scale will help
prevent wind erosion in areas such as the Rio Grande Valley, on Texas’ eastern
coast, and other coastal regions and ecosystems susceptible to erosion and whose
preservation is an increasingly valuable
aspect
of climate resilience.

For their experiments, the researchers got recycled-glass particles from a
company that diverts bottles from landfills, crushes them into particles and
tumbles the pieces to round off the edges. The final product is smooth enough
that people can handle the glass bits without getting cut, Quezada says.
Similarly, plant roots can easily grow around the glass pieces without being
harmed.

In initial tests, the researchers assessed the soil-like qualities, such as
compaction and water retention, of three different sizes of glass fragments.
They found that a size similar to coarse sand grains allowed oxygen to reach the
roots and maintain sufficient moisture levels that could be ideal for plant
cultivation.

Now, Quezada is evaluating the recycled-glass material as a viable substitute
for soil. In a greenhouse on campus, she’s growing cilantro, bell pepper and
jalapeño plants in a variety of pots containing anywhere from 100 percent
commercial potting soil to 100 percent recycled glass. Pots with more soil have
higher levels of nutrients required for plant growth — including nitrogen,
phosphorus and potassium — compared to those with more glass. But there’s little
variation in pH level among the pots — which is a promising result, because
plants thrive in a narrow soil pH range.

Early results also suggest that the plants grown in recyclable glass have faster
growth rates and retain more water, compared to those grown in 100 percent
traditional soil.

“A weight ratio of more than 50 percent of glass particles to soil appears best
for plant growth compared to the other mixtures we tested,” Vanegas says —
though the researchers are waiting until harvest time to confirm which soil
mixture produces the highest yields and tastiest produce.

Another noteworthy result is that pots with 100 percent potting soil developed a
fungus that stunted plant growth; Feria hypothesizes the fungus may impact
nutrient uptake by the roots. Pots that included any amount of recyclable glass
had zero fungal growth. The researchers are collecting data to determine
potential reasons for this.

Quezada says these results are particularly promising because the study was done
without fertilizers, pesticides or fungicides. From her experience working in
agriculture, she notes that a lot of the chemicals applied to
crops
and land can harm people — including her family members and the roughly 2.4
million farm
workers
and communities surrounding farms in the US alone.

“It’s really important to try to minimize the usage of any chemicals that can
negatively affect our health,” Quezada asserts. “If we are able to reduce them,
and help the community by collecting recyclables, then we can give people a
better quality of life.”

The research was funded by an Empowering Future Agricultural
Scientists grant from the US Department of
Agriculture’s National Institute of Food and Agriculture, and a US
National Science Foundation grant that’s also supporting Glass Half
Full — the community-focused recycling organization
that supplied the glass particles.