ABSTRACT
The chemical dehalogenation system discussed in this report is alkaline metal hydroxide/polyethylene glycol (APEG), which is applicable to aromatic halogenated compounds. The metal hydroxide that has been most widely used for this reagent preparation is potassium hydroxide (KOH) in conjunction with polyethylene glycol (PEG) [6, p. 461] 2 (typically, average molecular weight of 400 Daltons) to form a polymeric alkoxide referred to as KPEG [16, p. 835]. However, sodium hydroxide has also been used in the past and most likely will find increasing use in the future because of patent applications that have been filed for modification to this technology. This new approach will expand the technology’s applicability and efficacy and should reduce chemical costs by facilitating the use of less costly sodium hydroxide [18]. A variation of this reagent is the use of potassium hydroxide or sodium hydroxide/tetraethylene glycol, referred to as ATEG, that is more effective on halogenated aliphatic compounds [21]. In some KPEG reagent formulations, dimethyl sulfoxide (DMSO) is added to enhance reaction rate kinetics, presumably by improving rates of extraction of the haloaromatic contaminants [19; 22].
Previously developed dehalogenation reagents involved dispersion of metallic sodium in oil or the use of highly reactive organosodium compounds. The reactivity of metallic sodium and these other reagents with water presented a serious limitation to treating many waste matrices; therefore, these other reagents are not discussed in this chapter and are not considered APEG processes [1, p. 1].
The reagent (APEG) dehalogenates the pollutant to form a glycol ether and/or a hydroxylated compound and an alkali metal salt, which are water soluble by-products. This treatment process chemically converts toxic materials to nontoxic materials. It is applicable to contaminants in soil [11, p. 1], sludges, sediments, and oils [2, p. 183]. It is mainly used to treat halogenated contaminants including polychlorinated biphenyls (PCBs) [4, p. 137], polychlorinated dibenzo-p-dioxins (PCDDs) [11, p. 1], polychlorinated dibenzofurans (PCDFs), polychlorinated terphenyls (PCTPs), and some halogenated pesticides [8, p. 3; 14, p. 2]. This technology has been selected as a component of the remedy for three Superfund sites. Vendors should be contacted to determine the availability of a treatment system for use at a particular site. The estimated costs of treating soils range from $200 to $500/ton. This chapter provides information on the technology applicability, the types of residuals resulting from the use of the technology, the latest performance data, site requirements, the status of the technology, and where to go for further information.
