In 1978, EPA-sponsored research led to the development of the first in a series of APEG reagents, which effectively dechlorinate PCBs and oils. These reagents were alkali metal/polyethylene glycols which react rapidly to dehalo-genate halo-organic compounds of all types (Figure 11.15.11).
In the APEG reagents, alkali metal is held in solution by large polyethylene anions. PCBs and halogenated molecules are soluble in APEG reagents. These qualities combine in a single-phase system where the anions readily displace the halogen atoms. Halogenated aromatics react with PEGs resulting in the substitution of halogenated aromat-ics for chlorine atoms to form a PEG ether. The PEG ether decomposes to a phenol.
The effectiveness of APEG on general contaminant groups for various matrices is shown in Table 11.15.8 (U.S. EPA, 1990b).
A variation of APEG, referred to as ATEG, uses potassium hydroxide or sodium hydroxide/tetraethylene glycol, and is more effective on halogenated aliphatic compounds.
Figure 11.15.11 is a schematic of the APEG treatment process. Waste preparation includes excavating and/or moving the soil to the process where it is normally screened (1) removing debris and large objects and producing particles small enough to allow treatment in the reactor without binding the mixer blades.
Typically, reagent components are mixed with contaminated soil in the reactor (2). Treatment proceeds inefficiently without mixing. The mixture is heated to between 100°C and 180°C. The reaction proceeds for 1-5 hrs. depending upon the type, quantity, and concentration of the contaminants. The treated material goes from the reactor to a separator (3), where the reagent is removed and can be recycled (4).
During the reaction, water is evaporated in the reactor, condensed (5), and collected for further treatment or recycled through the washing process, if required. Carbon filters (7) are used to trap any volatile organics that are
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