Page 545 - Materials Chemistry, Second Edition

CAT3525_C16.qxd 1/27/2005 12:42 PM Page 516
516 Waste Management Practices: Municipal, Hazardous, and Industrial

TABLE 16.5
Organic Compounds Suitable for Sorption Treatment by
Activated Carbon
Class Example
Aromatic solvents Benzene, toluene, xylene
Polynuclear aromatics Naphthalene, biphenyl
Chlorinated aromatics Chlorobenzene, PCBs,
Endrin, toxaphene, DDT
Phenolics Phenol, cresol, resorcinol, nitrophenols,
chlorophenols, alkyl phenols
Aromatic amines and high- Aniline, toluene diamine
molecular weight aliphatic amines
Surfactants Alkyl benzene sulfonates
Soluble organic dyes Methylene blue, textiles, dyes
Fuels Gasoline, kerosene, oil
Chlorinated solvents Carbon tetrachloride, percholoroethyene
Aliphatic and aromatic acids Tar acids, benzoic acids
Pesticides/herbicides 2,4-D, atrazine, simazine, aldicarb,
alachlor, carbofuran
Source: U.S. EPA, 1984. With permission.

In smaller installations the carbon is removed and returned to the supplier for reprocessing (Wentz,
1995; Watts, 1998). Such regeneration processes will cause the carbon to lose some of its sorptive
qualities. Furthermore, about 10% of the carbon is lost with each regeneration.
All carbon contactors must be equipped with carbon removal and loading mechanisms to
allow spent carbon to be removed and virgin or regenerated carbon to be added. Spent, regenerated,
and virgin carbon are typically transported hydraulically by pumping as a slurry. Carbon slurries
may be transported with water or compressed air, centrifugal or diaphragm pumps, or eductors
(U.S. EPA, 2000b).
Carbon adsorption is generally cost-effective only when the contaminants are present in very
dilute quantities. Carbon adsorption is typically used to treat dilute aqueous streams with organics in
the low parts per million range. For wastewater streams that contain a significant quantity of indus-
trial flow, activated carbon adsorption is a proven, reliable technology to remove dissolved organics.
Space requirements are low. Granular activated carbon (GAC) adsorption can be easily incorporated
into an existing wastewater treatment facility. Disadvantages are also possible with the use of acti-
vated carbon for sorption. Under certain conditions, granular carbon beds may generate hydrogen
sulfide from bacterial growth, creating odors and corrosion problems. Spent carbon, if not regener-
ated, may present a land disposal problem. Wet GAC is highly corrosive and abrasive. Lastly, carbon
treatment requires pretreated wastewater with low suspended solids concentration. Variations in pH,
temperature, and flow rate may also adversely affect carbon adsorption (U.S. EPA, 2000).

16.3.6 STABILIZATION
Stabilization processes are accomplished by mixing hazardous waste with a binding agent to form
a crystalline or polymeric matrix that incorporates the entire waste. Inorganic binders include
cement, cement kiln dust, fly ash, and blast furnace slag. Organic wastes can be immobilized by the
addition of organic binders such as bitumen (asphalt) or polyethylene. Stabilization converts con-
taminants into a less- or a nonreactive form typically by chemical processes. Contaminants are fur-
thermore physically immobilized within a solid matrix in the form of a monolithic block. Thus,