TECHNOLOGY UPDATE Sprinkler irrigation destroys VOCs After a year of analysis by EPA's Superfund Innovative Technology Evaluation program, the agency has deemed the use of sprinkler irrigation systems for remediating groundwater contaminated by volatile organic compounds (VOCs) at levels below 1000 ppb acceptable and effective. The procedure incurs much lower costs than conventional pump-and-treat technologies, making it an important factor in considering water reuse opportunities for states that irrigate heavily. The concept of using irrigation sprinklers to remediate groundwater contaminated by VOCs was pursued by Roy Spaulding of the University of Nebraska Water Sciences Laboratory. Spaulding began experimenting with various sprinkler systems in 1993. Commercially available center-pivot and linear sprinklers proved capable of volatilizing VOCs. Sprinkler nozzle designs proved to be the most important determinant; "fog-type" nozzles worked best. According to Spaulding, the transfer efficiency of VOCs from water phase to gas phase increases as finer droplets are produced by the nozzle. Once released to the atmosphere, VOCs decompose in the presence of ultraviolet light. EPA's demonstration was held last summer at a site in Hastings, Neb., where groundwater had been contaminated by solvents from a municipal landfill and by fumigants released when a grain elevator exploded. Tests evaluated concentrations of five VOCs, including ethylene dibromide. The observed 9699% compound removal rate was comparable to performance achieved using conventional pumpand-treat techniques. Nebraska's Department of Health conducted a risk assessment to ensure that the quality of treated water conformed with federal guidelines for drinking water and with regulations of states likely to find the approach valuable. Nozzle effluent
Sprinkler irrigation technology is being used to efficiently remove VOCs from contaminated water at low cost (Courtesy Roy Spaulding)
mean contaminant concentrations were found to be below federal maximum contaminant levels. According to Spaulding, the average cost to conventionally treat water contaminated by VOCs at Superfund sites is between $20 million and $27 million over a 20-year period. In contrast, he estimates the total cost for sprinkler remediation at between $200,000 and $500,000. —KELLYN S. BETTS
Phyto-cleanup of lead progressing at N.J. site In less than seven weeks of cultivation, Indian mustard plants removed four times more contaminant lead than warranted by remediator Phytotech of Monmouth, N.J. Further demonstrating the ability of lead cleanup using phytoremediation, analysis of samples harvested at the field test site showed lead uptake exceeded 800 ppm on a plant dryweight basis, according to Steven Rock, the EPA field demonstration project coordinator. Soils at the site, formerly an industrial area occupied by manufacturers of Magic Marker pens and lead-acid batteries, include silty loam, sand and gravel, and rocky. The bulk of the lead is in the top six
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inches of the soil, making it an ideal candidate for phytoremediation with Indian mustard, Brassica juncea. Phytotech's Mike Blaylock attributes the impressive phytoremediation performance to use of chelates and other soil amendments. The warranted 200-ppm lead uptake level reflects the addition of some enhancements to contaminated soil at the site. Anticipated lead uptake by Indian mustard plants in unamended soil is about 100 ppm. In previous trials at the same site, Phytotech's Indian mustard plantings accumulated more than 12,000 ppm of lead from highly contaminated hot spots. Blaylock says the method is normally useful in areas where lead concentration levels are below 2000 ppm. The metal's ultimate bioavailability is influenced by lead speciation, plant growth factors, and other site-specific parameters. The Indian mustard was planted at the Magic Marker Superfund site in Trenton, N.J., in May. Phytotech's researchers expect the project to be completed by October 1998. Despite promising results from current field tests, EPA's Rock cautions, "It remains to be seen whether the phytoremediation will remove enough contaminants to reach the goal of 400 ppm, the overall soil concentra-
0013-936X/97/0931-496A$14.00/0 © 1997 American Chemical Society
tion level." New Jersey's cleanup goal for lead is below 400 ppm for residential areas and below 600 ppm for industrial zones. —K.S.B.
Nanosponges soak up contaminants Chemists at Los Alamos National Laboratory are evaluating the properties of "nanosponges," nanoporous polymeric materials that have an enormous ability to absorb organic chemicals. Laboratory tests of this new class of polymeric materials reveal that they exhibit a binding affinity 10,000-100,000 times greater than that of activated carbons for organic contaminants. According to Los Alamos researcher DeQuan Li, nanosponges should be useful for effectively remediating low-concentration organic contaminants in a wide variety of matrices. Potential applications include cleanup of hazardous organics in groundwater, treatment of municipal drinking water, and mitigation of oil spills and pollution associated with production and use of organic explosives. The polymers can be formed as granular solids, powders, optical thin films, and membranes. Li and his research partners have tested the nanosponge material's capacity for removing trichloroethylene, toluene, phenol, and sulfonate compounds from water samples. The new materials reduced contamination to the parts-per-trillion level, a cleanup efficiency at least 5 orders of magnitude greater than conventional treatment methods, including mitigation using various activated carbons and zeolites. The nanoporous polymers are based on cyclodextrins, which have a cylindrical, cage-like structure. In the presence of water, the hydrophobic cavities strongly attract contaminants, trapping them within. This absorptive behavior is reversible. In the presence of an organic solvent, like ethanol, the polymers can be induced to release trapped pollutants, effectively rinsing them free of contaminants and making the nanosponges reusable. According to Li, the nanoporous polymers are just one step away from commercialization. Because they can be made similarly to cyclodextrins, Li believes nanosponges could be mass-produced less expensively than activated carbons or zeolites. —K.S.B.
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