Super Absorbent Polymers (SAPs) are a class of three-dimensionally linked polymers that absorb large amounts of liquid relative to their own weight. When exposed to water, aqueous solutions, or oils, the polymers absorb relatively large amounts of liquid, up to 500 times their initial volume, while increasing the total weight of the system by a relatively small percentage. Superabsorbent polymers were developed in the 1960s by the USDA as a way to increase water retention in soil. As the technology developed, SAPs found applications in disposable hygienic products, replacing cellulose- and fiber-based products that absorbed up to only 20 times their weight. 
SAPs used for hazardous waste remediation and disposal present an alternative to the conventional method of using mineral-based absorbents. These SAPs have proven to be more effective at stabilizing the waste, fixing it within the polymers, and resulting in only a small increase in the total weight of the system compared to conventional methods. M2Polymers, Inc., a company that specializes in SAPs for applications like low-level radioactive waste stabilization and disposal, has used their products succesfully in the field. One example is the use of their WasteLock SAP to stabilize Cadmium, Chromium, and other soluble metals from sludge found on a former nuclear component manufacturer's site in order to pass the Toxic Characteristic Leaching Procedure (TCLP) required for acceptance to a disposal facility. The SAP was added to the waste through a series of troughs and mixing paddles. The stabilized mixture was then transferred to shipping containers to be transported to the disposal site, where all containers passed the TCLP and Paint Filter test. The estimated cost savings due to the neglible weight increase yielded by the SAPs compared to the conventional mineral-based absorbents is $2-3 Million. In other cases, this client had used mineral-based absorbents and the waste did not pass TCLP and was refused by waste facilities. Implementing the use of SAPs allowed the client's waste to pass TCLP and and to be transported at a much lower cost due to neglible weight increase from SAPs. For more information about this application of SAPs, visit: http://www.M2Polymer.com. For more information about SAPs for agricultural applications visit: http://www.watersorb.com.
SAPs are manufactured synthetically through polymerization, the process of reacting monomer molecules together in a chemical reaction to form three-dimensional polymer chains. They require the addition of small molecules to cross-link polymers together and the neutralization of the carboxyl acid groups along the polymer 'back bone'. These changes allow SAPs to function by drawing liquid in through osmosis along the neutralized 'back bone' of the polymer and forcing the SAP to expand, rather than separate, due to the cross-linking of the polymers that holds them together. With this basic structure, SAPs can be uniquely formed for specific purposes. For example, SAPs used for hazardous waste remediation are often sodium-based and non-biodegradable. SAPs for this application do not release solutions once they are absorbed, lending themselves to hazardous waste remediation and disposal. SAPs used for agricultural applications are often potassium-based and releast water over time to plants. These SAPs will eventually biodegrade into non-toxic elements. Sodium-based SAPs are less suited for agricultural applications as they have a shorter effective live span and created unwanted salinity levels in the soil.
SAPs used for hazardous waste remediation and disposal present an alternative to the conventional method of using mineral-based absorbents. These SAPs have proven to be more effective at stabilizing the waste, fixing it within the polymers, and resulting in only a small increase in the total weight of the system compared to conventional methods. M2Polymers, Inc., a company that specializes in SAPs for applications like low-level radioactive waste stabilization and disposal, has used their products succesfully in the field. One example is the use of their WasteLock SAP to stabilize Cadmium, Chromium, and other soluble metals from sludge found on a former nuclear component manufacturer's site in order to pass the Toxic Characteristic Leaching Procedure (TCLP) required for acceptance to a disposal facility. The SAP was added to the waste through a series of troughs and mixing paddles. The stabilized mixture was then transferred to shipping containers to be transported to the disposal site, where all containers passed the TCLP and Paint Filter test. The estimated cost savings due to the neglible weight increase yielded by the SAPs compared to the conventional mineral-based absorbents is $2-3 Million. In other cases, this client had used mineral-based absorbents and the waste did not pass TCLP and was refused by waste facilities. Implementing the use of SAPs allowed the client's waste to pass TCLP and and to be transported at a much lower cost due to neglible weight increase from SAPs. For more information about this application of SAPs, visit: http://www.M2Polymer.com. For more information about SAPs for agricultural applications visit: http://www.watersorb.com.
Portland District, U.S. Army Corps of Engineers (Summer Lake, OR)
BioHaven® Floating Islands are constructed floating treatment wetlands composed of a buoyant mat planted with wetland or garden plants . They are used to filter nitrates, phosphates, heavy metals, and other run-off contaminants while creating a micro-habitat for surrounding species, enhancing the ecology of the water body. These buoyant mats are constructed with a matrix of fibers in which one could describe as a “pot-scrub” or “loofah”. This matrix is composed of 100% recycled plastic from drinking bottles whose layers are bonded together using marine foam, another factor in providing the mats’ buoyancy. Floating Islands may be customized to any form or size. Larger islands are built using a modular system, reinforced for extra buoyancy, yet still maintaining flexibility of movement in water. Floating Islands may be installed in ponds, lakes, rivers, or streams; they are typically anchored or tethered in place however, they sometimes are left to float freely across the water’s surface.
In February 2009, the U.S. Army Corps of Engineers installed an experimental application of a Floating Island in the Summer Lake Wildlife Area at Dutch Lake, Oregon, to address an endangered salmon population. Caspian terns annually feast on over 4 million juvenile salmon in the Columbia River estuary. The floating island was launched in order to deter the Caspian terns from the estuary and to create a new habitat and nesting location. This island is the largest of its kind, 22,000 square-fee, and was launched without any vegetation, as it was prohibited.
A crew of 13 installers assembled the modular 22,000-square-foot island on a ramp adjacent to the lake. Each of the 328 modules measured 5 feet by 14 feet, using 200 pounds of polypropylene from recycled carpet and 125 pounds of polyester from recycled plastic drinking bottles. With only a 5-week window between the waterfowl hunting and bird migrating seasons, the island had to be quickly constructed upon the arrival of its parts. As pieces were assembled, they were partially slid into the lake, leaving one side afloat in water and the other still on dry territory to connect to the next group of modules. The crew stapled tree fabric along the top of modules in several groupings to prevent plant growth, over which they spread a 7-inch layer of pumice as the tern’s nesting material. Once completed, the island was brought to the middle of the water by boats and was anchored in place. In mid-May, researchers had counted a range of individuals from 8-33, while some were digging in preparation for egg-laying. On May 17, the first tern egg was spotted on the floating island, followed by an additional eight tern nests with eggs. The Army Corps is currently designing a 30,000-square-foot floating island for Sheepy Lake in Northern California, part of a plan to build eight more islands.
Other applications of BioHaven® Floating Islands include the Chicago River in the Diversey Park area, Zoo Montana’s Otter Enclosure, and the Lake Simcoe Watershed Project in Barrie, Ontario, while Floating Island International, the creators of the floating islands, continuously do their own research and record their findings in Montana.
-- Catherine De Almeida
References and Images:
Bird Research Northwest
Floating Island International
U.S. Army Environmental Command
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