Glass-fragment waste typically just ends up in landfills, but perhaps that doesn't always have to be the case. A new study shows that ground glass particles can be mixed with soil to produce a plant growth medium that's actually better than soil alone.
Although relatively large glass items can be recycled into more glass of the same color, small pieces of glass of various colors are too small and fiddly to efficiently sort for recycling. As a result, although efforts to change this fact are underway, large quantities of those little bits are usually just dumped.
Given the fact that both glass and sand are composed mainly of silica, scientists at The University of Texas Rio Grande Valley set out to see if ground glass particles could take the place of sand in a plant growth medium. Not only would this action divert that glass from landfills, it would also decrease the need for mined sand, which is in increasingly short supply.
Led by professors Julie Vanegas and Teresa Patricia Feria Arroyo, the researchers obtained glass particles from a company that crushes bottles destined for landfills, then tumbles the resulting particles to round off their sharp edges. Three sizes of those particles were mixed with commercial potting soil, in ratios ranging all the way from 100% glass particles to 100% soil.
The scientists then set about growing cilantro, bell pepper and jalapeño plants in pots of the different growth media, under otherwise identical greenhouse conditions.
It was initially found that when the particles were roughly the size of coarse grains of sand, oxygen was best able to reach the plants' roots, and optimum moisture levels were maintained. And importantly, because the particles had been tumbled, they didn't cut the roots growing around them.
The researchers did note that plants grown in mixes of mainly potting soil contained higher levels of nutrients such nitrogen, phosphorus and potassium, which are necessary for plant growth. That said, plants grown in mixes of over 50% glass particles (by weight) actually grew faster than those in 100% potting soil, plus they retained more water. pH levels fell in the same range for all of the mixes.
The faster growth rate was likely due to the fact that all of the pots with 100% soil developed a fungus which is known to stunt plant growth. That fungus didn't occur in any of the pots that contained any amount of glass particles – the scientists are currently trying to determine why this was the case.
Whatever the answer may be, it is hoped that if recycled glass is ultimately utilized in farm soil on a commercial scale, it will reduce the need for problematic fertilizers, pesticides, and fungicides.
"I think it's really important to try to minimize the usage of any chemicals that can negatively affect our health," says chemistry graduate student Andrea Quezada, who is presenting the team's findings at the fall meeting of the American Chemical Society. "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 effect of the glass particles on factors such as yield and taste will be determined when the plants are harvested.
Source: American Chemical Society
