Glass is thought to be the oldest manufactured substance in the world. In fact, archaeologists have found glass bottles and jars dating back to 1500 B.C. In ancient times, glass was considered a craft used for decorative purposes and to make containers to hold food. Fast forward past the Industrial Revolution and to more modern times: Now glass is made in mass quantities and holds everything from beer to jelly. According to the EPA, Americans generate a whopping 12.5 million tons of glass waste every year.
The good news is that Americans are embracing recycling programs in record numbers. The EPA estimates that over 30% of the waste produced by Americans during 2000 actually ended up in recycling programs. One such use for recycled glass is that it is now replacing sand as a water-filtration medium.
Crushed glass in water filters isn’t that far off the beaten path. After all, most glass is made from silica sand, soda ash, and limestone. To recycle the glass, it is processed through a series of crushers, dryers, and screens to remove contaminants, and the result is a product that looks and feels like plain white beach sand. So sand is used to make glass and then the glass is made back into a sandlike substance.
Research in the United States
There has been some research as to the effectiveness of recycled glass in water filtration in the US. Most of this research has been overseen by the Clean Washington Center (CWC), of Seattle, WA. The CWC’s focus and mission has been to develop markets, technologies, and beneficial end uses for recycled materials. The CWC has managed and documented more than 90 projects validating recycling technologies or recycled content products, and has developed Best Practices In Recycling for several recyclable commodities.
For example, a pilot project was conducted for the city of Roslyn, WA, to evaluate the feasibility of using crushed, recycled glass as a filtration medium in slow sand filters. The population of Roslyn is approximately 900, and the source of the city’s drinking water is the Domarie Creek. The study used a 15-inch PVC pipe as the media container and Steilacoom sand, Trinidad Pit sand, Ellensburg sand, and crushed glass to evaluate the effectiveness of slow-rate filtration on Domarie Creek surface water. Each column contained 36 inches of filter medium underlain by several layers of support gravels of coarseness increasing with depth.
During the study, the maximum contaminant level (MCL) given in the State Administrative Code for monthly average turbidity was violated using the glass sand column for one month associated with a storm event, but was otherwise in compliance. Two of the other three columns also violated the monthly MCL for one month. The Ellensburg sand was the only medium that held the effluent turbidity within the mandated MDL for the duration
of the study.
The results of the study indicated that slow-rate filtration with either sand or glass may be an effective treatment process for the city of Roslyn raw water source with the addition of a roughing filter or other method of pretreatment and/or the capability to divert raw water during high turbidity events.
Another study conducted by the CWC focused on crushed glass as a filter medium for the onsite treatment of wastewater. The results of this study indicated that the glass performed as well as the sand in the split filter system. In 1996, following this two-year study, the Washington State Onsite Wastewater Technical Review Committee approved the use of recycled crushed glass for the use in sand filters.
As promising as these two studies proved to be, most progress on the U.S. front since that time seems to have stalled. This may be due in part to the loss of funding provided to the CWC for such studies.
Progress Abroad
Even though progress has come to a standstill in the US, that is not the case in the UK, where an organization similar to the CWC has emerged. The Waste & Resources Action Program (WRAP), was established in 2001 in response to the British government’s Waste Strategy 2000 to promote sustainable waste management. WRAP has been involved in several studies involving recycled glass as a water filtration media.
One such study evaluated the potential of recycled glass as a water filtration medium for the treatment of drinking water and industrial effluents. The study was conducted between October 2002 and March 2004 at water and wastewater treatment facilities and was financed by Edinburgh, Scotland-based Dryden Aqua Ltd, developer of the UK’s first commercial recycled glass filtration media product, Active Filter Media (AFM), and the EC Life-Environment Fund. The results of the study indicate that recycled glass media, exemplified by AFM, can perform better than traditional sand media by improving treatment efficiency (up to 30% due to improved resistance to biofouling and contamination), by lowering backwash rates (up to 50%), and by improving process stability and longevity within the filter.
Another case study, conducted at the Ford Motor Company Ltd. manufacturing estate in the UK, showed that recycled glass could offer long-term cost and performance benefits. Ford ran a trial using AFM at its Dagenham effluent water treatment plant. Previously, the sand used in the filtration system had degenerated quickly, becoming clogged with dirt. It also required replacing every couple of months, which was very costly. Ford was also looking to find a product that could effectively filter the water so that it could be recycled back into the system. This would also help reduce the cost of discharging water.
Ford ran comparative trials for three months using AFM recycled glass filtration media and traditional sand in a test bed at the plant. The filtration, processing capabilities, and durability of each material were examined. Samples of the effluent water were tested each week for dirt and particle levels. During this trial, AFM continued to be effective with no biofouling or fall in its filtration efficiency. Also less back-flushing was required, reducing the need for chemicals and chlorine. Ford also found that less AFM is required compared to sand.
Other trials have yielded positive results at various industries such as a chemical plant, paper mill, and food processing plant.
Companies in The US
There are a few companies in the US that are recycling glass for various products including water filtration. Since 1996, TriVitro has been developing recycled glass products. Based in Kent, WA, the company has processed more than 25,000 tons of recycled glass. TriVitro has three product lines VitroHue, VitroGrit, and VitroClean. VitroClean is specially sized and colored glass for use in terrazzo flooring, tiles, counter tops, panels, and craft purposes. This recycled glass is also tumbled to achieve an “ocean-worn” appearance for a wide variety of applications. VitroGrit is crushed glass that is used for abrasive cleaning, surface preparation, and blasting. VitroClean is finely crushed glass that is used in pool, industrial, and environmental filtration.
Jeff Freas, head of sales and marketing at TriVitro, says that the company’s product is primarily used in the filtration of swimming pools, storm water drainage and industry applications. Crushed glass has advantages over sand filtration, according to Freas. “Generally what is found is that because of the structure of the glass grain as opposed to a silica sand grain it tends to clog up less and you get better filtration,” he says. “When you backwash a system it will backwash more easily.”
The grains of the recycled glass have a slight negative charge on their surface, which tend to hold onto fine particles during the filtration cycle. Upon backwashing, this weak charge releases these fine particles to the effluent, thereby contributing to better filtration action.
There are a couple of other companies in the US that dabble in the recycling of crushed glass for filtration. One is Opta Minerals Inc., a Waterdown, ON-based company with production and warehouse facilities in Virginia, Louisiana, California, South Carolina, Maryland, and New York. Another company, Strategic Materials Inc., of Houston, TX, collects both post-industrial and post-consumer scrap glass and processes it into a raw material called “cullet.” The cullet is then primarily sold to glass container and fiberglass manufacturers for use as a raw material in their glass production processes. Strategic Materials operates a network of 31 processing plants and aggregation depots across the US, Canada, and Mexico.
Pros and Cons
All of the case studies involving crushed glass as a filtration medium have provided glowing results. Some studies indicated crushed glass works just as good if not better than silica sand in filtration. Other studies indicated that crushed glass provides improved water treatment efficiency, lower backwash rates, and lower costs—not to mention the environmental benefits of using recycled glass and keeping it out of the landfills.
There are, however, some notable disadvantages to using crushed glass as opposed to sand in water filtration. According to literature from the EPA, alterative media filters are not proven technologies and no long-term operating data are available for crushed glass media. Another disadvantage is that since the filter medium is unique, it may not be readily available when it must be replaced. These two factors may be why crushed glass is not utilized more in the US as a filtration media in water, wastewater, and industry treatments.
NIKKI STILES is a freelance writer based in the city of Fairmont, WV.
OW - July/August 2006 |
