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and volatile organic compounds. Normal water disinfection and filtration treatment steps remove or destroy the bulk of these materials (65). However, treatment by activated carbon is an important additional step in many plants to remove toxic and other organic materials (66-68) for safety and palatability.

Groundwater Remediation

Concern over contaminated groundwater sources increased in the 1980s, and in 1984 an Office of Groundwater Protection was created by the EPA (36pp.731.2000V-731.2001L). This led to an increase in activated carbon consumption in 1987 for groundwater treatment to about 4% of the total liquid-phase usage, and further growth is expected in the 1990s. There are two ways to apply carbon in groundwater cleanup. One is the conventional method of applying powdered, granular, or shaped carbon to adsorb contaminants directly from the water. The other method utilizes air stripping to transfer the volatile compounds from water to air. The compounds are then recovered by passing the contaminated air through a bed of carbon (69,70).

Industrial and Municipal Wastewater Treatment

Wastewater treatment consumes about 21% of the total U.S. liquid-phase activated carbon (36pp.731.2000V-731.2001L), and governmental regulations are expected to increase demand over the next several years. Wastewater may contain suspended solids, hazardous microorganisms, and toxic organic and inorganic contaminants that must be removed or destroyed before discharge to the environment. In tertiary treatment systems, powdered, granular, or shaped carbon can be used to remove residual toxic and other organic compounds after the primary filtration and secondary biological treatment (71). Powdered carbon is also used in the PACT process by direct addition of the carbon to the secondary biological step (41pp.389-447).

Sweetener Decolorization

About 21% of the liquid-phase activated carbon is used for purification of sugar (qv) and corn syrup (36pp.731.2000V-731.2001L). White sucrose sugar is made from raw juice squeezed from sugarcane or sugar beets. The clarified liquor is decolorized using activated carbon or ion exchange resins (58pp.87-125,274-292). High-fructose corn sweeteners (HFCS) are produced by hydrolysis of corn starch and are then treated with activated carbon to remove undesirable taste and odor compounds and to improve storage life. The demand for HFCS rose sharply in the 1980s primarily because of the switch by soft drink producers away from sucrose (83).

Chemical Processing

Activated carbon consumption in a variety of chemical processing applications is about 8% of the total (36pp.731.2000V-731.2001L). The activated carbon removes impurities to achieve high quality. For example, organic contaminants are removed from solution in the production of alum, soda ash, and potassium hydroxide

(58pp.87-125,274-292). Other applications include the manufacture of dyestuffs, glycols, amines, organic acids, urea, hydrochloric acid, and phosphoric acid (35pp.92-135).

Food, Beverage, and Cooking Oil

Approximately 6% of the liquid-phase activated carbon is used in food, beverage, and cooking oil production (36pp.731.2000V-731.2000L). Before being incorporated into edible products, vegetable oils and animal fats are refined to remove particulates, inorganics, and organic contaminants. Activated carbon is one of several agents used in food purification processes. In the production ofalcoholic beverages, activated carbon removes haze-causing compounds from beer, taste and odor from vodka, and fusel oil from whiskey (58pp.87-125,274-292). The feed water for soft drink production is often treated with carbon to capture undesirable taste and odor compounds and to remove free chlorine remaining from disinfection treatment. Caffeine is removed from coffee beans by extraction with organic solvents, water, or supercritical carbon dioxide prior to roasting. Activated carbon is used to remove the caffeine from the recovered solvents (35pp.92-135).

Pharmaceuticals

Pharmaceuticals account for 6% of the liquid-phase activated carbon consumption (36pp.731.2000V-731.2000L). Many antibiotics, vitamins, and steroids are isolated from fermentation broths by adsorption onto carbon followed by solvent extraction and distillation (58pp.87-125,274-292). Other uses in pharmaceutical production include removal of chromogenic impurities, process water purification, and removal of impurities from intravenous solutions prior to packaging (35pp.92-135).

Mining

The mining industry accounts for only 4% of liquid-phase activated carbon use, but this figure may grow as low-grade ores become more common (36pp.731.2000V-731.2000L). Gold, for example, is recovered on activated carbon as a cyanide complex in the carbon-in-pulp extraction process (58pp.87-125, 274-292). Activated carbon serves as a catalyst in the detoxification of cyanides contained in wastewater from cyanide stripping operations (46pp.8-19). Problems caused by excess flotation agent concentrations in flotation baths are commonly cured by adding powdered activated carbon (58pp.87-125,274-292).

Miscellaneous Uses

Several relatively low-volume activated carbon uses comprise the remaining 6% of liquid-phase carbon consumption (36pp.731.2000V-731.2000L). Small carbon filters are used in households for purification of tap water. Oils, dyes, and other organics are adsorbed on activated carbon in dry cleaning recovery and recycling systems. Electroplating solutions are treated with carbon to remove organics that can produce imperfections when the thin metal layer is deposited on the substrate (58pp.87-127,274-292). Medical ap plications include removal of toxins from the blood of patients with artificial kidneys (35pp.92-135), and oral ingestion into the stomach to recover poisons or toxic materials (58pp.87-125,274-292;72). Activated carbon also is used as a support for metal catalysts in low-volume production of high-value specialty products such as pharmaceuticals, fragrance chemicals, and pesticides (73).

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  • mentha puddifoot
    What is g for cell culture?
    8 years ago

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