1.4.3 Chemical Treatments
This strategy should be used with caution since some difficulties may potentially
occur. The main issues are related to both the use and the storage of chemicals on
site, the potential increase in waste volume, the occurrence of hazardous or
unwanted reactions. Unwanted reactions in the treated soils or within the regeneration units may hinder or even quench the expected reactions and lower treatment
yields. For example, oxidation is rarely specific, while soil and leachates are loaded
with various components that consume oxidant (Haselow et al. 2003). Finally, the
use of chemicals in the regeneration units may also over-contaminate the treated sites
if they are carried along in the reused leaching solutions.
1.4.3.1 Oxidation
The selective degradation of PAHs from soil leachates in presence of CDs or Tween
80 using electro-Fenton oxidation has been studied (Mousset et al. 2014, 2016;
Trellu et al. 2017). PAHs degradation larger than 99% was achieved after 4–8 h,
while the recovery rates for ligands were higher for CDs (approximately 90%) than
for Tween 80 (50–79%), because of different mechanisms and accessibility to PAHs
in the complexes. The best conditions for the selective degradation of PAHs in
presence of Tween 80 were observed at low current density. Despite the toxicity of
treated leachates remained high, in particular because of the production of more
hydrophilic oxygenated metabolites, their reuse for soil washing did not show any
loss for soil bioactivity. The reported energy consumption for this electro-Fenton
process was in the range 0.36–0.69 kWh g
À1 TOC removed. Considering a usual
TOC about 800 mg l
À1 for a PAH-contaminated soil leachate, the energy consumed
for degradation would be higher than 90 € m
À3 of treated wastewater.
1.4.3.2 Reduction
A catalytic hydrodechlorination was used to partially degrade pentachlorophenol
into cyclohexane. This soil leachate was obtained from poly-contaminated soil
leachates (Rivero-Huguet and Marshall 2011) in the presence of EDDS and Brij
98 (nonionic surfactant) after solvent extraction. The reported reduction yield was
60% and whereas it did not seem of immediate economic interest, the idea of
degrading organic contaminants by reductive ways is attractive and deserves to be
mentioned.
40
N. Fatin-Rouge
This strategy should be used with caution since some difficulties may potentially
occur. The main issues are related to both the use and the storage of chemicals on
site, the potential increase in waste volume, the occurrence of hazardous or
unwanted reactions. Unwanted reactions in the treated soils or within the regeneration units may hinder or even quench the expected reactions and lower treatment
yields. For example, oxidation is rarely specific, while soil and leachates are loaded
with various components that consume oxidant (Haselow et al. 2003). Finally, the
use of chemicals in the regeneration units may also over-contaminate the treated sites
if they are carried along in the reused leaching solutions.
1.4.3.1 Oxidation
The selective degradation of PAHs from soil leachates in presence of CDs or Tween
80 using electro-Fenton oxidation has been studied (Mousset et al. 2014, 2016;
Trellu et al. 2017). PAHs degradation larger than 99% was achieved after 4–8 h,
while the recovery rates for ligands were higher for CDs (approximately 90%) than
for Tween 80 (50–79%), because of different mechanisms and accessibility to PAHs
in the complexes. The best conditions for the selective degradation of PAHs in
presence of Tween 80 were observed at low current density. Despite the toxicity of
treated leachates remained high, in particular because of the production of more
hydrophilic oxygenated metabolites, their reuse for soil washing did not show any
loss for soil bioactivity. The reported energy consumption for this electro-Fenton
process was in the range 0.36–0.69 kWh g
À1 TOC removed. Considering a usual
TOC about 800 mg l
À1 for a PAH-contaminated soil leachate, the energy consumed
for degradation would be higher than 90 € m
À3 of treated wastewater.
1.4.3.2 Reduction
A catalytic hydrodechlorination was used to partially degrade pentachlorophenol
into cyclohexane. This soil leachate was obtained from poly-contaminated soil
leachates (Rivero-Huguet and Marshall 2011) in the presence of EDDS and Brij
98 (nonionic surfactant) after solvent extraction. The reported reduction yield was
60% and whereas it did not seem of immediate economic interest, the idea of
degrading organic contaminants by reductive ways is attractive and deserves to be
mentioned.
40
N. Fatin-Rouge