06-25 broken glass bottle

[Image above] Credit: Ivan Radic, Flickr (CC BY 2.0)

By Becky Stewart

Glass is one of the most environmentally friendly packaging materials in today’s market. Its durability allows it to be used for much longer than paper-based packaging, and it typically does not leach chemicals into the environment like plastic products. Although manufacturing glass is quite energy intensive, the material is theoretically 100% recyclable. As such, it drastically reduces the need to mine new raw materials and so improves the material’s overall score on a life cycle assessment.

And yet, these benefits are not being realized in the United States, where glass recycling rates have stagnated at approximately 30%. Why is the potential of such a recyclable material going unrealized, and what can be done to revive glass recycling?

This blog post started when I read about the looming sand crisis for concrete and an accompanying shortage of pure quartz for silicon semiconductor manufacturing. Being the problem-solver I am, I wondered why we couldn’t use some of our unrecycled glass, which is anywhere from 55–99% silica, to ease some of these shortages? Approximately 7 million tons of glass go to U.S. landfills every year, so that’s a lot of potential to help address various market needs. I wrote this blog post to bring you (some of) the answers to these important questions.

What drives demand for recycled glass?

Glass recycling rates are much higher in many other parts of the world than they are in the U.S., and consumers are beginning to take notice. Concerns about carbon emissions, the emissions’ effects on global warming, and individual ways to reduce emissions are making average citizens more conscious of their glass waste.

However, meaningful change in glass recycling rates will require systemic changes to current waste disposal, collection, and recycling processes as well as identifying markets for recycled glass.

Potential markets for recycled glass

Turning glass bottles and jars into new glass containers is an obvious potential market, but it requires the glass to be separated by color, which can be laborious manual work that few recycling centers are doing. Technology exists to automate optical sorting by glass color, but it is expensive. Like any good capitalist system, though, as demand increases, costs will decrease.

Moving outside the box for ideas, I was curious if the semiconductor industry could make use of recycled glass. From the U.S. to Europe to Asia, semiconductor manufacturing is charging full steam ahead. As governments and companies work to establish these new fabrication plants, they will need access to silicon in two forms: high-purity silicon for the chip itself, and high-purity quartz crucibles to melt the silicon in.

At this point, using recycled glass to fulfill either need is not feasible due to the purity requirement. Regular glass bottles contain a wide range of additives to modify the color and mechanical properties, among other characteristics. Although methods exist for extracting silicon dioxide from waste glass, the extracted material would not be pure enough for semiconductor applications. Additional processing would be necessary, and even after great cost, the required purity to produce single-crystal silicon wafers may not be achievable.

This fact, on top of the already resource-intensive and caustic extraction process, means it does not make sense economically to use recycled glass as a source of silicon for semiconductors. But maybe, in the future, new purification methods will change this paradigm.

The concrete industry, conversely, could make great use of recycled glass. Replacing some of the sand in concrete with crushed recycled glass has many advantages. In addition to increasing the workability of wet concrete,  fine powdered glass has positive effects on the final mechanical properties and durability of concrete. However, alkali–silica reactions, which can cause the concrete to swell and degrade, must be mitigated.

Drawbacks aside, concrete additives are a viable use for recycled glass that could replace some of the sand in concrete, freeing up natural sand for other applications.

There are several additional industrial uses for recycled glass:

To take full advantage of recycled glass in these applications, though, the recycling industry in the U.S. will need to overcome some hurdles to effectively collect and process glass.

Hurdles to glass recycling

As described below, there are a few key reasons why glass recycling has fallen behind in the U.S.

  • Contamination: When glass bottles and jars are not cleaned properly before disposal—or get mixed with other types of glass, such as from windows, mirrors, or colored glass—it contaminates the entire batch. Contaminated glass cannot be recycled into new food and beverage containers.
  • Transportation costs: Glass is heavy and relatively low value, making it expensive to transport over long distances to recycling processors. It does not have to arrive intact, at least!
  • Lack off end markets: With a decline in U.S. glass manufacturing, there are fewer end markets for recycled glass cullet. Some recyclers have been landfilling or stockpiling glass due to lack of demand. (Shipping the glass cullet to manufacturers is not economical because of the transportation costs.)
  • Confusion over recycling rules: Conflicting rules between municipalities over which types of glass are accepted has led to consumer confusion and lower participation.

Potential solutions

Several initiatives, listed below, could help revive U.S. glass recycling.

  • Improved education: Clear guidelines on which glass items are recyclable, along with more promotion of glass recycling benefits, could boost participation. Purer cullet streams can be achieved by moving to collection centers that keep glass out of single-stream recycling.
  • Developing local end markets: Supporting new regional uses for recycled glass cullet, such as construction materials or countertops, provides local outlets.
  • Consumer demand: Wineries and, to a lesser extent, breweries are banding together to encourage their customers to return bottles to the source for reuse. Labels that wash off easily are available to make the process even easier.
  • Recycling innovations: New technologies, such as optical sortation, and incentives, such as deposit return schemes, can produce very high-quality cullet streams.

One such regional innovation is being undertaken by a collaboration of Goodwill Industries outlets in Delaware, Maryland, and the District of Columbia. They developed a plan and accompanying infrastructure to reuse the unsellable glass items donated to their stores. The recycling center for Goodwill of Delaware and Delaware County was the first of three regional centers to receive a grant-funded industrial glass crusher. Their plan is to produce enough glass cullet to be sold as art supplies or manufacturing raw materials.

Although glass recycling faces real economic and logistical hurdles, the material is too valuable to waste. With some creative thinking and a focus on developing robust, regional cullet markets, we can give new life to our old bottles and jars.