HA and OGI Soil HA at 5 mg L
À1 each) due to competitive adsorption on
iron surface, but the presence of quinone compounds (juglone and AQDS)
increased the reduction rate due to mediated electron-transfer. However, they suggest that the effects will not be much significant in field applications as the
observed effects were low. Doong and Lai (2005) have shown that low concentration
of humic acids (<50 mg L
À1 ) decreases PCE dechlorination rate by Pd/Fe particles;
normalized constant rates of dechlorination decrease from 33.47 L m
À2 h
À1
without humic acid to 16.86 L m
À2 h
À1 at 5 mg L
À1 and 1.69 L m
À2 h
À1 at
50 mg L
À1 of humic acid. Similar observations for 1,1,1-TCA degradation by
biochar supported Ni/Fe nanoparticles were reported, with the inhibitory effect
explained by the adsorption of humic acid on active surface site (Li et al. 2017a).
Doong and Lai (2006) have also studied the effect of metal ions in the absence and
the presence of humic acid, with a decrease of constant rates in the presence of humic
acid (Table 6.17).
Generally, the presence of macromolecules, which are abundant in the subsurface, results in a decrease in iron reactivity due to the blocking of reactive site
through adsorption, complexation, or a combination of both (Bhattacharjee and
Ghoshal 2018).
Porphyrins that are naturally produced in subsurface, such as vitamin B 12
(cobalamine), are good catalysts for the reductive dechlorination of COCs, and
work as electron transfer mediators in the presence of an electron donor. If titanium(III) citrate is generally used as the reductant (Burris et al. 1996, 1998;
Glod et al. 1997; Dror and Schlautman 2004), an enhanced reductive
dechlorination by nZVI particles with vitamin B 12 is also observed (Amir and
Lee 2011). Hence, the addition of vitamin B 12 model compounds (cobaloximes)
has been proposed for COCs catalytic degradation (McCauley et al. 2002; Pizarro
et al. 2018).
Table 6.17 Dechlorination rate constants of PCE by ZVI in the presence of divalent metal and
humic acid (from Doong and Lai 2006)
System
Without humic acid
With humic acid
k obs (h
À1
)
k SA (L m
À2 h
À1
)
k obs (h
À1
)
k SA (L m
À2 h
À1 )
ZVI
9.6
(Æ1.7) Â 10
À3
3.43
(Æ0.61) Â 10
À3
1.5
(Æ0.06) Â 10
À3
0.54
(Æ0.02) Â 10
À3
ZVI + Cu
(II)
22.9
(Æ6.5) Â 10
À3
8.24
(Æ2.32) Â 10
À3
4.8
(Æ0.7) Â 10
À3
1.71
(Æ0.25) Â 10
À3
ZVI + Co
(II)
16.7
(Æ3.5) Â 10
À3
5.96
(Æ1.23) Â 10
À3
6.1
(Æ0.6) Â 10
À3
2.15
(Æ0.22) Â 10
À3
ZVI + Ni
(II)
809
(Æ16) Â 10
À3
289 (Æ6) Â 10
À3
256
(Æ41) Â 10
À3
91 (Æ16) Â 10
À3
6 In Situ Chemical Reduction of Chlorinated Organic Compounds
337
À1 each) due to competitive adsorption on
iron surface, but the presence of quinone compounds (juglone and AQDS)
increased the reduction rate due to mediated electron-transfer. However, they suggest that the effects will not be much significant in field applications as the
observed effects were low. Doong and Lai (2005) have shown that low concentration
of humic acids (<50 mg L
À1 ) decreases PCE dechlorination rate by Pd/Fe particles;
normalized constant rates of dechlorination decrease from 33.47 L m
À2 h
À1
without humic acid to 16.86 L m
À2 h
À1 at 5 mg L
À1 and 1.69 L m
À2 h
À1 at
50 mg L
À1 of humic acid. Similar observations for 1,1,1-TCA degradation by
biochar supported Ni/Fe nanoparticles were reported, with the inhibitory effect
explained by the adsorption of humic acid on active surface site (Li et al. 2017a).
Doong and Lai (2006) have also studied the effect of metal ions in the absence and
the presence of humic acid, with a decrease of constant rates in the presence of humic
acid (Table 6.17).
Generally, the presence of macromolecules, which are abundant in the subsurface, results in a decrease in iron reactivity due to the blocking of reactive site
through adsorption, complexation, or a combination of both (Bhattacharjee and
Ghoshal 2018).
Porphyrins that are naturally produced in subsurface, such as vitamin B 12
(cobalamine), are good catalysts for the reductive dechlorination of COCs, and
work as electron transfer mediators in the presence of an electron donor. If titanium(III) citrate is generally used as the reductant (Burris et al. 1996, 1998;
Glod et al. 1997; Dror and Schlautman 2004), an enhanced reductive
dechlorination by nZVI particles with vitamin B 12 is also observed (Amir and
Lee 2011). Hence, the addition of vitamin B 12 model compounds (cobaloximes)
has been proposed for COCs catalytic degradation (McCauley et al. 2002; Pizarro
et al. 2018).
Table 6.17 Dechlorination rate constants of PCE by ZVI in the presence of divalent metal and
humic acid (from Doong and Lai 2006)
System
Without humic acid
With humic acid
k obs (h
À1
)
k SA (L m
À2 h
À1
)
k obs (h
À1
)
k SA (L m
À2 h
À1 )
ZVI
9.6
(Æ1.7) Â 10
À3
3.43
(Æ0.61) Â 10
À3
1.5
(Æ0.06) Â 10
À3
0.54
(Æ0.02) Â 10
À3
ZVI + Cu
(II)
22.9
(Æ6.5) Â 10
À3
8.24
(Æ2.32) Â 10
À3
4.8
(Æ0.7) Â 10
À3
1.71
(Æ0.25) Â 10
À3
ZVI + Co
(II)
16.7
(Æ3.5) Â 10
À3
5.96
(Æ1.23) Â 10
À3
6.1
(Æ0.6) Â 10
À3
2.15
(Æ0.22) Â 10
À3
ZVI + Ni
(II)
809
(Æ16) Â 10
À3
289 (Æ6) Â 10
À3
256
(Æ41) Â 10
À3
91 (Æ16) Â 10
À3
6 In Situ Chemical Reduction of Chlorinated Organic Compounds
337