During the first 6 month after connecting the DC field, there was a significant
decrease in DCE, VC, and total ClE concentrations. Since well IS4 was not directly
used for infiltration of nZVI and it was located in the centre of the DC field, it
demonstrated the effect of spatial reduction of contaminants throughout the treated
area. Decreases were relatively rapid in this low permeable environment and therefore cannot be completely interpreted by the groundwater flow from the cathode,
where hydrogenation of ClE may occur directly on the electrode. Unlike the
application of nZVI only, the ClE concentrations remained low and did not rebound
during the whole period when the DC field was used. Replacement of the anodes and
additional infiltration of nZVI had no effect on the ClE concentrations. The entire
system was shut down in M63, when the electrodes were no longer active. The ClE
concentrations subsequently increased because of the flow of contaminated water
from the surroundings.
4.3.2.4 Changes in Geochemical Conditions
The geochemical conditions in the rock environment change by a direct current. An
essential fact is that the E h -pH conditions in the rock environment shift beyond the
field of stability of goethite, the most common mineral phase of Fe
3+ . This phase is
insoluble under normal conditions. The electric field maintains nZVI and its decomposition products in the field of stability of Fe
2+ , which allows the prolongation of
the nZVI activity in the structure. The geochemical conditions in the monitoring
boreholes at the site most frequently correspond to the field of stability of Fe
(HCO 3 )
À and near the cathode Fe(OH) 4
À . Part of the Fe
2+ is captured in the pyrite
structure, including the sulfides entering the treated area in the groundwater. In the
given environment, the water is in contact with marlstone and the products of its
weathering, so it is significantly enriched with the carbonate ion. From the point of
view of the final target mineral phase, the iron is transformed in the rock environment in addition to pyrite, magnetite, siderite, and the occurrence of iron hydroxide
is not excluded, as demonstrated by the results of the laboratory experiments.
Magnetite and siderite are partially soluble in a decreasing pH to normal values so
they can re-dose the environment with Fe
2+ ions, which plays an important role in
the process of the reductive dechlorination of ClE.
References
Bennett P, He F, Zhao D, Aiken B, Feldman L (2010) In situ testing of metallic iron nanoparticle
mobility and reactivity in a shallow granular aquifer. J Contam Hydrol 116:35–46. https://doi.
org/10.1016/j.jconhyd.2010.05.006
Černík M, Nosek J, Filip J, Hrabal J, Elliott DW, Zbořil R (2019) Electric-field enhanced reactivity
and migration of iron nanoparticles with implications for groundwater treatment technologies:
proof of concept. Water Res 154:361–369. https://doi.org/10.1016/j.watres.2019.01.058
4 Combination of Electrokinetics and nZVI Remediation
83
decrease in DCE, VC, and total ClE concentrations. Since well IS4 was not directly
used for infiltration of nZVI and it was located in the centre of the DC field, it
demonstrated the effect of spatial reduction of contaminants throughout the treated
area. Decreases were relatively rapid in this low permeable environment and therefore cannot be completely interpreted by the groundwater flow from the cathode,
where hydrogenation of ClE may occur directly on the electrode. Unlike the
application of nZVI only, the ClE concentrations remained low and did not rebound
during the whole period when the DC field was used. Replacement of the anodes and
additional infiltration of nZVI had no effect on the ClE concentrations. The entire
system was shut down in M63, when the electrodes were no longer active. The ClE
concentrations subsequently increased because of the flow of contaminated water
from the surroundings.
4.3.2.4 Changes in Geochemical Conditions
The geochemical conditions in the rock environment change by a direct current. An
essential fact is that the E h -pH conditions in the rock environment shift beyond the
field of stability of goethite, the most common mineral phase of Fe
3+ . This phase is
insoluble under normal conditions. The electric field maintains nZVI and its decomposition products in the field of stability of Fe
2+ , which allows the prolongation of
the nZVI activity in the structure. The geochemical conditions in the monitoring
boreholes at the site most frequently correspond to the field of stability of Fe
(HCO 3 )
À and near the cathode Fe(OH) 4
À . Part of the Fe
2+ is captured in the pyrite
structure, including the sulfides entering the treated area in the groundwater. In the
given environment, the water is in contact with marlstone and the products of its
weathering, so it is significantly enriched with the carbonate ion. From the point of
view of the final target mineral phase, the iron is transformed in the rock environment in addition to pyrite, magnetite, siderite, and the occurrence of iron hydroxide
is not excluded, as demonstrated by the results of the laboratory experiments.
Magnetite and siderite are partially soluble in a decreasing pH to normal values so
they can re-dose the environment with Fe
2+ ions, which plays an important role in
the process of the reductive dechlorination of ClE.
References
Bennett P, He F, Zhao D, Aiken B, Feldman L (2010) In situ testing of metallic iron nanoparticle
mobility and reactivity in a shallow granular aquifer. J Contam Hydrol 116:35–46. https://doi.
org/10.1016/j.jconhyd.2010.05.006
Černík M, Nosek J, Filip J, Hrabal J, Elliott DW, Zbořil R (2019) Electric-field enhanced reactivity
and migration of iron nanoparticles with implications for groundwater treatment technologies:
proof of concept. Water Res 154:361–369. https://doi.org/10.1016/j.watres.2019.01.058
4 Combination of Electrokinetics and nZVI Remediation
83