A New Use for Mixed Glass Cullet
By Trish Thiel
Using crushed glass cullet in certain wastewater, storm water, swimming pool and personal water septic system filters is growing in some communities.
Water treatment systems that send water through a filter usually contains sand. The sand filters out impurities. Research has shown crushed glass can also be used to do this, with at least the same, and sometimes, even better results than with sand.
The small town of Oswego, New York, located on the shores of Lake Ontario, is one town where the filtering system using the glass is in place and working. In 1997 the town had to replace its wastewater treatment plant.
Town supervisor, Jack Tierney, said, "We came upon this system through the engineer that we contracted to design the plant. He had given us options, including using sand or glass. The bottom line was that the glass system was less expensive."
In the Oswego area glass cullet is priced slightly cheaper than sand. Also, the sand in this area of the state just falls into the requirements for filtering systems. The glass can be crushed to a size that is better for the system.
The engineer on the Oswego project, Richard Elliott, P.E., said, "the sand that is available locally for Oswego just barely meets the state standards. The crushed glass they used was absolutely at the other end of the standards scale and was perfect for the project. The glass was coarser and more uniform in size than the local sand."
Oswego purchased its glass for the project from Nexcycle Resources, Inc., in Syracuse, New York, a glass container processor. The company gets its glass from curbside collections and deposit returns. Most of the glass that Nexcycle processes is sorted and sold to container manufacturers. For its mixed cullet, Nexcycle makes the filter media and also construction aggregate.
Frank Nolan, Nexcycle plant manager, said, "For the wastewater system a smaller material was needed so we had to get a fine screen that would take the glass down to 3/8 of an inch."
The company uses a HazMag crusher and a vibration screen system to filter glass to the proper size for the different products. Mr. Nolan said it does cost a little more to make the filter media, as compared to construction aggregate because there is more processing.
"This is a good outlet for this glass, but is a very sporadic market and right now it is very regionalized. This glass can be used in what is called a slow sand filter. The Oswego system was the first one in the state. We had to make the glass meet the standards of the state and the New York Environmental Conservation Department. The Oswego project used about 11,000 tons. A ton of glass is pretty close to a cubic yard."
Mr. Nolan added that the first project was the hardest. "We do get other inquires for the slow sand filters. Most other purchases are around 30 to 40 tons for home septic systems. In New York, in areas where the land is not suitable for a leachate field and there is no municipal sewer system, septic tanks need to be installed. This type of filtering is used in these systems."
Mr. Elliot said that the key to making this market grow is to be able to manufacture this product cheaper than the natural material. He said there are some other benefits from using glass instead of sand.
"In and of itself, glass might be a little better than natural sand. There is hardly any change in glass over time, as there is with sand. Sometimes sand dissolves a little. The biggest problem with sand is that the filters can get plugged. The coarser the material the less it gets plugged. The glass can be manufactured to be coarser."
Mr. Tierney added, "After five years we have had some settling in the glass. That's five years that we haven't had to replace anything. I was amazed the first time I saw the product. You could tell it was broken up glass. It was all about the same size though and I knew it was a good thing to reuse this product."
Another area of the country that has been using or testing glass in filtering systems is in Washington. TriVitro in Seattle, Washington is a glass processor. They have supplied glass for a project that is filtering storm water run off from a parking lot area.
Dan Freas, owner of TriVitro, said, "So far the glass has been working great. In the storm water project, the project was first started over three years ago. At that time the testing had two filters, one with sand and one with glass. The sand failed and the glass kept working, so they put in all glass. The glass media is expected to last for at least four or five years."
In this area though, the glass product is more expensive than natural sand.
"There is very little demand for the glass in the wastewater and storm water projects because of the cost. We are able to compete in the swimming pool and spa filter markets with our product," said Mr. Freas. "The sand is priced higher for swimming pools, so our product becomes comparable in costs. When people use the glass their overall costs will actually be lower because they use less glass than sand and the product last longer and does a better job filtering the water. I would venture to say that glass, in these types of applications would last three, even four, times longer."
To meet standards in Washington, the glass has to be free of all debris. Mr. Freas said it can be a challenge to get rid of all the paper and glue. In New York it is not necessary to get rid of all the paper and glue for wastewater treatment systems.
Mr. Freas added, "This product is really the 'which comes first; the chicken or the egg'. In this area you can't get people to switch because of cost, but if more people would use the product the cost would come down with larger production amounts."