in leachates (TPH approximately 1000 mg l
À1 ) from a creosote-contaminated soil
could be removed while the SDS recovery was about 9% only. The main concerns
with this method is the risk to favor anionic surfactant precipitation in soil leading to
soil pore clogging when the coagulant is introduced in excess during the wastewater
treatment. Cationic surfactant like cetyltrimethylammonium bromide (CTAB) have
been proposed as an alternative to inorganic coagulants (Hirasaki et al. 2011), but
their price precludes their use in this context. Electrocoagulation was proposed for
the simultaneous regeneration of EDTA at pH 10 from Pb–EDTA complexes
(Pociecha and Lestan 2010). Lead was recovered both at the cathode and in Al
oxyhydroxides; however, Faraday yields for metal recovery are usually low in
alkaline conditions (Awal Abdilahi 2015) and ligand recovery depends strongly on
pH value. Similarly, Ferraro (2015) reports the use of iron electrodes for the
regeneration of Cu-contaminated EDDS solutions. However, despite Cu being
removed from EDDS, the new form of the ligand was unclear and some caution
must be taken with respect to regeneration, since Fe complexes of EDDS are
kinetically quite inert and have stability constants similar to Cu–EDDS.
1.4.2.3 Solvent Extraction
This technique is usually used for the removal of neutral contaminants or ion pairs
obtained with a companion molecule. It has been used for the fast regeneration of
cyclodextrins from PAH-contaminated soil leachates using colza oil (Petitgirard
et al. 2009). A pilot-scale experiment using a closed loop automated system showed
the preserved activity for the regenerated solution despite the numerous performed
cycles, thanks to the quantitative CD recovery through regeneration. Despite the
interest of this low cost, high efficiency, and eco-friendly regeneration process, the
use of CDs has limited interest for field applications. The regeneration of
HOC-contaminated surfactant solutions has been also tested with various organic
solvents (Lee et al. 2002; Ehsan et al. 2007; Ahmed Mohamed 2014). However,
there is a real concern for secondary pollution since their solubility in water is still
enhanced by surfactants. The higher the surfactant concentration is in aqueous
solution, the lower the partition constant is for HOCs between the organic phase
and the aqueous phase (Kungsanant et al. 2008). For creosote-contaminated soil
leachates with surfactant concentrations at 2%, the partition constant ranged from
80 to 4, following the order ethyl acetate > petroleum ether > diethyl ether > methyl
tert-butyl ether (MTBE). The nature of the polar head of the surfactant has little
influence on the value of its o/w partition coefficient. The use of organic solvent
represents a real danger for workers and moreover, it changes the properties of the
treated wastewater; hence, except for ex situ treatments, it is not recommended.
1 Contaminant Mobilization from Polluted Soils: Behavior and Reuse of Leaching. . .
39
À1 ) from a creosote-contaminated soil
could be removed while the SDS recovery was about 9% only. The main concerns
with this method is the risk to favor anionic surfactant precipitation in soil leading to
soil pore clogging when the coagulant is introduced in excess during the wastewater
treatment. Cationic surfactant like cetyltrimethylammonium bromide (CTAB) have
been proposed as an alternative to inorganic coagulants (Hirasaki et al. 2011), but
their price precludes their use in this context. Electrocoagulation was proposed for
the simultaneous regeneration of EDTA at pH 10 from Pb–EDTA complexes
(Pociecha and Lestan 2010). Lead was recovered both at the cathode and in Al
oxyhydroxides; however, Faraday yields for metal recovery are usually low in
alkaline conditions (Awal Abdilahi 2015) and ligand recovery depends strongly on
pH value. Similarly, Ferraro (2015) reports the use of iron electrodes for the
regeneration of Cu-contaminated EDDS solutions. However, despite Cu being
removed from EDDS, the new form of the ligand was unclear and some caution
must be taken with respect to regeneration, since Fe complexes of EDDS are
kinetically quite inert and have stability constants similar to Cu–EDDS.
1.4.2.3 Solvent Extraction
This technique is usually used for the removal of neutral contaminants or ion pairs
obtained with a companion molecule. It has been used for the fast regeneration of
cyclodextrins from PAH-contaminated soil leachates using colza oil (Petitgirard
et al. 2009). A pilot-scale experiment using a closed loop automated system showed
the preserved activity for the regenerated solution despite the numerous performed
cycles, thanks to the quantitative CD recovery through regeneration. Despite the
interest of this low cost, high efficiency, and eco-friendly regeneration process, the
use of CDs has limited interest for field applications. The regeneration of
HOC-contaminated surfactant solutions has been also tested with various organic
solvents (Lee et al. 2002; Ehsan et al. 2007; Ahmed Mohamed 2014). However,
there is a real concern for secondary pollution since their solubility in water is still
enhanced by surfactants. The higher the surfactant concentration is in aqueous
solution, the lower the partition constant is for HOCs between the organic phase
and the aqueous phase (Kungsanant et al. 2008). For creosote-contaminated soil
leachates with surfactant concentrations at 2%, the partition constant ranged from
80 to 4, following the order ethyl acetate > petroleum ether > diethyl ether > methyl
tert-butyl ether (MTBE). The nature of the polar head of the surfactant has little
influence on the value of its o/w partition coefficient. The use of organic solvent
represents a real danger for workers and moreover, it changes the properties of the
treated wastewater; hence, except for ex situ treatments, it is not recommended.
1 Contaminant Mobilization from Polluted Soils: Behavior and Reuse of Leaching. . .
39