TECHNOLOGY UPDATE based carbon filters can be made for $0.70-1.00/lb. Cost information for filters that are currendy on die market is not available, but their selling prices range between $1.20 and $1.50/lb. Ion-exchange resins sell for $1 to $20/lb. ARS is currendy investigating the potential of the hulls of soybeans, cottonseed, and rice—as well as the shells of other nuts grown in the United States—for use in activated carbon filters.
Activated carbon filters from pecan shells The U.S. Department of Agriculture (USDA) is applying to patent an inexpensive means of creating carbon filters. The key ingredient is pecan shells, charred to a carbon-rich crisp. By activating and oxidizing those carbons, scientists have devised a filter that removes metals as well as the usual organic pollutants from industrial wastewater. The USDA's cooperative research and development partner is currentiy devising a manufacturing process for the filters and expects them to be on the market in mid-1998. The original goal of die project was to transform an agricultural waste product into something useful. In the process, the USDA's Agricultural Research Service (ARS) produced a product with the potential to cost less than other granulated activated carbon filters and outperform them. "We spent a lot of time and refined the technology to the point where our nutshells can adsorb organics and metals better than more than six of the commercial filters we've tested " said ARS chemist Wayne Marshall. Marshall's lab in New Orleans has two methods for activating the carbons in the shells. In one method, the shells are immersed in acid before their trip through the furnace. The other method sends them straight into the oven, where they are fired in a carbon dioxide-rich environment. The goal of both activation methods is to maximize the surface area of the granulated carbon particles so that the largest possible amount of target material will adhere to them. Thus activated, both kinds of pecan shell filters adsorbed more industrial solvents than the activated carbon filters they were tested against. More than 60% of the activated carbon filters sold to take up organic pollutants are made from coal (for example, the Calgon Filtrasorb 400, a popular filter for water treatment that ARS used in compar-
Drinking water treatment system zaps microbes
Crushed pecan shells (top) toasted to activated carbon (bottom) are being fine-tuned to adsorb metals in industrial wastewater. (Courtesy Sandia National Laboratory)
ative testing). The tests required the filters to isolate pollutants from an aqueous mixture of six small molecular weight organics, including methanol, acetone, and toluene. The pecan shell carbons are oxidized after being activated to allow them to take up metal ions. Metal ions are a particular target of USDA's partner, Rio Grande Environmental Products, LLC, of Albuquerque, N.M. Inspired by the steady supply of shells from the pecan orchards in southern New Mexico, Rio Grande hopes to sell the filters to the state's metal-plating and jewelry industries. Accordingly, ARS has fine-tuned the filters for adsorbing copper. In comparative tests, the acid-activated pecan shell filters adsorbed three times more copper than a commercial peatbased filter, according to Marshall. The pecan shell filters' facility for taking up copper may allow them to replace the more expensive ion-exchange resins usually used to remove metals from solution, Marshall said. He estimates that the nutshell-
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A promising new technology to destroy Cryptosporidium in drinking water, considered a potential "gold mine" by EPA evaluators, recentiy failed its first round of large-scale tests at EPA's Cincinnati laboratory. The water treatment system, which uses a nonchemical method that physically destroys microbial contaminants, won a two-year EPA cooperative R&D agreement. The patented technology uses a combination of ultrasound, electromagnetic fields, and ultraviolet light to destroy microbes. The large-scale chamber, which can handle 150 gal/ min, has a highly polished mirrorlike coating. The beams are reflected off the coating and "blow up" the organisms, said EPA scientist James Goodrich. During early stages of testing at the Office of Research and Development's test and evaluation facility in Cincinnati last November, the bench-scale model replicated the company's results, but the largescale model failed, said Goodrich. The system's developer, Phoenix Water Systems, Inc., of Spokane, Wash., believes the chamber coating in the larger model was substandard. Company officials will resume testing after the chamber is recoated. Under the cooperative agreement, EPA and Phoenix staff work together to confirm the company's claims and improve the system's operation. EPA will also analyze operat-
0013-936X/97/0931-120AS14.00/0 © 1997 American Chemical Society
