January 1, 2008
Across the country, local governments are faced with the challenge of meeting recycling goals, reducing solid waste tonnage and minimizing costs. Glass is one of the most challenging materials to recycle, with most county and city recycling programs incurring net costs to recycle the material. Over the years, several alternative uses for recycled glass have been identified, such as “glassphalt” and landscaping applications. However, a Florida program evaluating the feasibility of using pulverized recycled glass for beach renourishment may provide a cost-effective approach for managing this material.
In the July 2005 issue of Waste Age, an article entitled “Beach in a Bottle” (www.wasteage.com/mag/waste_beach_bottle/index.html) described a project that Broward County, Fla., is conducting to investigate the feasibility of using recycled glass for beach renourishment. The following is an update on that project.
The first phase was designed to gauge public perception of the project while conducting a comparative analysis of the properties of natural beach sand and the artificial sand made from glass cullet. On the public perception side, tourism officials and beach professionals were very interested in the concept, while Broward County residents found the idea equally appealing. Meanwhile, geotechnical and contaminant analyses of grain size, distribution, munsell color, carbonate content, grain angularity and chemical composition revealed that glass cullet compares closely to natural sand.
More recently, the county has been conducting additional research to determine the long-term viability of using recycled glass for beach erosion control and renourishment.
Aquarium and Abiotic Testing
In 2005, the county developed a biological analysis program to monitor the survivability of fish and other fauna species within specific proportions of natural sand and glass cullet. Species then were introduced into a matrix comprised of varying ratios of cullet and natural sand. The species' ability to survive was monitored for any deviations from natural sand. The glass cullet utilized for these and subsequent tests was similar in grain size to natural beach sand (approx. 0.33 to 0.90 mm). After two months of testing, officials determined that pulverized glass cullet does not adversely affect macro or microorganisms. The species studied displayed normal active behavior with the glass cullet and showed no adverse signs of physical stress. Results indicated that the organism mortality rate was equivalent to natural sand.
In March 2006, a test plot was constructed on the upland portion of Hollywood Beach for a six-month experiment to determine if glass cullet mixtures exhibit the same abiotic characteristics (temperature, moisture content, gas exchange) when compared to natural beach sand. The test plot simulated a sea turtle hatchery enclosure and contained 16 individual test areas, each measuring 5 feet square and 3 feet deep. The results indicated that the glass cullet/sand mixtures displayed no significant difference from natural sand, and the mixtures could allow for proper sea turtle embryo development.
The overall results of the geotechnical, public perception, aquarium and abiotic tests indicate that the project is technically feasible. In Broward County, the presence of nesting loggerhead turtles and the beach-based economy create unique concerns that must be considered and addressed in all beach erosion control and renourishment efforts. However, research shows that manufacturing a sand product from recycled glass is a promising solution anywhere beaches are eroding and glass is a net cost to recycle.
Broward County currently is permitting phase two of this demonstration project, which will involve experimental testing at the shoreline on Hollywood Beach. Approximately 2,000 cubic yards of pulverized glass cullet will be placed at the shoreline, allowing the county and its project consultants to monitor its performance and evaluate its similarities to the existing beach sand when subjected to wind and waves. Specifically, the testing will determine if glass cullet can be used to address erosion “hot spots” on the beach, which are smaller areas that suffer from critical erosion problems. As part of this phase, the county also will be investigating the feasibility of long-term methods of producing the pulverized glass.
Peter Foye, Director, Recycling and Contract Division, Broward County, Fla.; Phil Bresee, Recycling Program Manager, Broward County, Fla.; Sanford Gutner, PE, Senior Associate, Malcolm Pirnie Inc.; Holly M. P. Burton, PE, Associate, Malcolm Pirnie Inc.; Ryann M. Davis, Engineer, Malcolm Pirnie Inc.