weight for each oxidative and reducing reagent is calculated by dividing the molar
mass by the number of electrons transferred in half-reactions (Table 6.7).
Equivalent weight ¼
Molar mass
Number of electrons transferred
ð6:35Þ
The stoichiometric ratio can then be determined by dividing the equivalent weight
of the reductant by the equivalent weight of the chlorinated organic compound
(Eq. 6.36). SRD is then calculated from the total mass of pollutant (dissolved,
adsorbed, and DNAPL).
Stoichiometric ratio ¼
Equivalent weight of reductant
Equivalent weight of COC
ð6:36Þ
For in situ application, the stoichiometric requirement is highly impacted by
non-beneficial reactions (natural reductant demand, NRD), because of the presence
of natural occurring oxidants such as water, dissolved oxygen, or natural organic
matter (Shi et al. 2015). Hence, higher dosage is generally necessary to reach a
complete dechlorination, especially to compensate iron passivation and the adsorption/reduction of metal ions on iron surface. NRD is quite different from natural
oxidant demand (NOD) because water is in large abundance in environmental
conditions compared to indigenous oxidizable materials (Fan et al. 2016b). Hydrogen evolution rate (HER) can be measured by H 2 evolution or by using a colorimetric redox indicator (Fan et al. 2015).
Also, it is important to identify the corresponding oxidation equation depending
on environmental conditions (equilibrium speciation, kinetically controlled metastable phases and spatial heterogeneity) (Tratnyek et al. 2014).
6.3.4 Reaction Kinetics and Chemical Dechlorination
Pathways
6.3.4.1 Rate Equations
In subsurface environment, COCs degradation kinetics are influenced by the rate of
all abiotic degradation reactions previously reported (Sect. 6.2.4), e.g., the rate of
hydrolysis, dehydrochlorination, reduction, and oxidation reactions. The overall
equation is:
r ¼ r hydrolysis þ r dehydrochlorination þ r reduction þ r oxidation
ð6:37Þ
where all rates r—assumed to occur independently and in parallel—are in
mol L
À1 s
À1 .
6 In Situ Chemical Reduction of Chlorinated Organic Compounds
315
mass by the number of electrons transferred in half-reactions (Table 6.7).
Equivalent weight ¼
Molar mass
Number of electrons transferred
ð6:35Þ
The stoichiometric ratio can then be determined by dividing the equivalent weight
of the reductant by the equivalent weight of the chlorinated organic compound
(Eq. 6.36). SRD is then calculated from the total mass of pollutant (dissolved,
adsorbed, and DNAPL).
Stoichiometric ratio ¼
Equivalent weight of reductant
Equivalent weight of COC
ð6:36Þ
For in situ application, the stoichiometric requirement is highly impacted by
non-beneficial reactions (natural reductant demand, NRD), because of the presence
of natural occurring oxidants such as water, dissolved oxygen, or natural organic
matter (Shi et al. 2015). Hence, higher dosage is generally necessary to reach a
complete dechlorination, especially to compensate iron passivation and the adsorption/reduction of metal ions on iron surface. NRD is quite different from natural
oxidant demand (NOD) because water is in large abundance in environmental
conditions compared to indigenous oxidizable materials (Fan et al. 2016b). Hydrogen evolution rate (HER) can be measured by H 2 evolution or by using a colorimetric redox indicator (Fan et al. 2015).
Also, it is important to identify the corresponding oxidation equation depending
on environmental conditions (equilibrium speciation, kinetically controlled metastable phases and spatial heterogeneity) (Tratnyek et al. 2014).
6.3.4 Reaction Kinetics and Chemical Dechlorination
Pathways
6.3.4.1 Rate Equations
In subsurface environment, COCs degradation kinetics are influenced by the rate of
all abiotic degradation reactions previously reported (Sect. 6.2.4), e.g., the rate of
hydrolysis, dehydrochlorination, reduction, and oxidation reactions. The overall
equation is:
r ¼ r hydrolysis þ r dehydrochlorination þ r reduction þ r oxidation
ð6:37Þ
where all rates r—assumed to occur independently and in parallel—are in
mol L
À1 s
À1 .
6 In Situ Chemical Reduction of Chlorinated Organic Compounds
315