Although the use of ZVI particles should result in VC circumvention (Arnold and
Roberts 2000), the progressive decrease in ZVI reactivity, associated with the
growth and transformation of the oxide shell, can lead to a change in the degradation
pathways from β-elimination to hydrogenolysis, in agreement with the accumulation
of VC.
The treatment effect of nZVI particles was emphasized in DCC2.3 regarding the
results acquired between June 2 and June 22. From August 2014 to June 2, 2015, the
use of nZVI particles resulted in the drastic decrease in cis-1,2-DCE content
(44–46%), 1,1-DCE content (52–53%) and, in a lesser extent, in TCE content
(10–13%), which was already rather low. In the same time, VC content only
increased up to 11–13%. In comparison with the data obtained for DCC2.2, these
results are in a better agreement with the use of nZVI. They clearly evidenced that
ZVI circumvented VC (Arnold and Roberts 2000). In comparison to DCC2.2, these
results can be explained by the rather low content of TCE in the cPZ. Data acquired
in June 22 clearly highlighted the results obtained during June 2 campaign. The
decrease in ZVI reactivity was nevertheless clearly evidenced versus time, from June
22 to July 8 with a progressive increase in TCE content and its degradation products.
In comparison with the data acquired at laboratory scale, the use of nZVI resulted
in higher reductions (up to 60% versus 10% at laboratory scale). This result can be
explained by a symbiosis between the implementation of the reductive process and
the natural attenuation occurring on site. This hypothesis is supported by the results
acquired for alkalinity, which remained in the same order of magnitude versus time.
6.5.3.4 Line 3: nZVI and Dithionite
Innovative injection techniques have been used to inject sequentially nZVI at four
levels into DCI3:
• Level 1: April 2, 2015: injection of 1 canister of nZVI solution: water flowrate of
400 L h
À1 and nZVI solution flowrate of 84 mL min
À1 ; i.e., continuously
12.6 mL of nZVI per liter of water
• Level 2: April 3, 2015: injection of 1 canister of nZVI solution: water flowrate of
375 L h
À1 and nZVI solution flowrate of 84 mL min
À1 ; i.e., continuously
13.44 mL of nZVI per liter of water
• Level 3: April 7, 2015: injection of 1 canister of nZVI solution: water flowrate of
321 L h
À1 and nZVI solution flowrate of 84 mL min
À1 ; i.e., continuously
5.70 mL of nZVI per liter of water
• Level 4: April 9, 2015: injection of 1 canister nZVI solution
From May 18 to June 18, 2015, only dithionite was injected simultaneously at the
four levels as follows: injection at 20 L h
À1 of a 150 g L
À1 dithionite solution diluted
on line to reach a flowrate of 200 L h
À1 (an average of 3 kg of dithionite were
injected each hour during 1 month with a constant flowrate of 200 L h
À1 ).
6 In Situ Chemical Reduction of Chlorinated Organic Compounds
365
Roberts 2000), the progressive decrease in ZVI reactivity, associated with the
growth and transformation of the oxide shell, can lead to a change in the degradation
pathways from β-elimination to hydrogenolysis, in agreement with the accumulation
of VC.
The treatment effect of nZVI particles was emphasized in DCC2.3 regarding the
results acquired between June 2 and June 22. From August 2014 to June 2, 2015, the
use of nZVI particles resulted in the drastic decrease in cis-1,2-DCE content
(44–46%), 1,1-DCE content (52–53%) and, in a lesser extent, in TCE content
(10–13%), which was already rather low. In the same time, VC content only
increased up to 11–13%. In comparison with the data obtained for DCC2.2, these
results are in a better agreement with the use of nZVI. They clearly evidenced that
ZVI circumvented VC (Arnold and Roberts 2000). In comparison to DCC2.2, these
results can be explained by the rather low content of TCE in the cPZ. Data acquired
in June 22 clearly highlighted the results obtained during June 2 campaign. The
decrease in ZVI reactivity was nevertheless clearly evidenced versus time, from June
22 to July 8 with a progressive increase in TCE content and its degradation products.
In comparison with the data acquired at laboratory scale, the use of nZVI resulted
in higher reductions (up to 60% versus 10% at laboratory scale). This result can be
explained by a symbiosis between the implementation of the reductive process and
the natural attenuation occurring on site. This hypothesis is supported by the results
acquired for alkalinity, which remained in the same order of magnitude versus time.
6.5.3.4 Line 3: nZVI and Dithionite
Innovative injection techniques have been used to inject sequentially nZVI at four
levels into DCI3:
• Level 1: April 2, 2015: injection of 1 canister of nZVI solution: water flowrate of
400 L h
À1 and nZVI solution flowrate of 84 mL min
À1 ; i.e., continuously
12.6 mL of nZVI per liter of water
• Level 2: April 3, 2015: injection of 1 canister of nZVI solution: water flowrate of
375 L h
À1 and nZVI solution flowrate of 84 mL min
À1 ; i.e., continuously
13.44 mL of nZVI per liter of water
• Level 3: April 7, 2015: injection of 1 canister of nZVI solution: water flowrate of
321 L h
À1 and nZVI solution flowrate of 84 mL min
À1 ; i.e., continuously
5.70 mL of nZVI per liter of water
• Level 4: April 9, 2015: injection of 1 canister nZVI solution
From May 18 to June 18, 2015, only dithionite was injected simultaneously at the
four levels as follows: injection at 20 L h
À1 of a 150 g L
À1 dithionite solution diluted
on line to reach a flowrate of 200 L h
À1 (an average of 3 kg of dithionite were
injected each hour during 1 month with a constant flowrate of 200 L h
À1 ).
6 In Situ Chemical Reduction of Chlorinated Organic Compounds
365