33.3.1.6 Fe Concentration
Determination of concentration of total and dissolved iron in groundwater (or in
sediment collected from the bottom of monitoring/injection wells) is probably the
most straightforward method for tracing the nZVI distribution in the aquifer. It can
immediately show the elevated amount of nanoparticles under the assumption that
the background Fe concentration is low. On-site Fe determination can be performed
by portable spectrophotometer for measurement absorbance of Fe
0 and Fe
2+ in
groundwater after complexation reaction with ferrozine and phenanthroline, respectively. If higher precision and more reliable results are needed, iron content can be
measured using atomic absorption spectrometry (AAS) or inductively coupled
plasma (ICP) spectroscopic techniques in laboratories. In this case, additional steps
as sample conservation, transport, and pretreatment are required. The samples are
usually processed according to a standard EPA method 3005. Prior to the determination of dissolved Fe, nZVI and its transformation products can be removed
magnetically and the sample is then filtered through 0.2 μm syringe filter.
33.3.1.7 Tracer Concentration
Another way to elucidate the impact of nZVI application is the use of a conservative
tracer. An inert substance (usually lithium iodide, bromide ions, or contrast dye, e.g.,
fluorescein) is added to the nZVI suspension prior to its injection and the concentration of this element in groundwater is subsequently determined. An ideal tracer is
highly soluble in the water and does not undergo substantial transformation or
sorption to the soil and rocks. Due to the fact that this substance is dissolved in a
liquid part of nZVI suspension, its migration does not exactly follow the migration of
nanoparticles, but it rather reflects movement of the injected fluid and displays
changes in the flow of groundwater within the aquifer.
33.3.1.8 Concentration of Contaminants and Their Degradation
Products
The position of reactive nanoparticles within the aquifer can also be deduced
indirectly from measuring the levels of target contaminants and/or their degradation
products. It is possible to monitor the total concentration of the target contaminant as
well as its speciation (e.g., oxidation states of metals). In the case of chlorinated
hydrocarbons (CHCs), particular pollutants as well as their sum can be measured.
Concentration of volatile organic compounds (VOCs, common pollutants treated by
nZVI) can be determined directly at the site using membrane interface probe—MIP
(find more in Chap. 31). Nevertheless, much more common protocol involves
groundwater sampling and its subsequent analysis in a laboratory employing gas
chromatography–mass spectrometry (GC-MS, Fig. 33.8). Therefore, special
640
P. Skácelová and J. Filip
Determination of concentration of total and dissolved iron in groundwater (or in
sediment collected from the bottom of monitoring/injection wells) is probably the
most straightforward method for tracing the nZVI distribution in the aquifer. It can
immediately show the elevated amount of nanoparticles under the assumption that
the background Fe concentration is low. On-site Fe determination can be performed
by portable spectrophotometer for measurement absorbance of Fe
0 and Fe
2+ in
groundwater after complexation reaction with ferrozine and phenanthroline, respectively. If higher precision and more reliable results are needed, iron content can be
measured using atomic absorption spectrometry (AAS) or inductively coupled
plasma (ICP) spectroscopic techniques in laboratories. In this case, additional steps
as sample conservation, transport, and pretreatment are required. The samples are
usually processed according to a standard EPA method 3005. Prior to the determination of dissolved Fe, nZVI and its transformation products can be removed
magnetically and the sample is then filtered through 0.2 μm syringe filter.
33.3.1.7 Tracer Concentration
Another way to elucidate the impact of nZVI application is the use of a conservative
tracer. An inert substance (usually lithium iodide, bromide ions, or contrast dye, e.g.,
fluorescein) is added to the nZVI suspension prior to its injection and the concentration of this element in groundwater is subsequently determined. An ideal tracer is
highly soluble in the water and does not undergo substantial transformation or
sorption to the soil and rocks. Due to the fact that this substance is dissolved in a
liquid part of nZVI suspension, its migration does not exactly follow the migration of
nanoparticles, but it rather reflects movement of the injected fluid and displays
changes in the flow of groundwater within the aquifer.
33.3.1.8 Concentration of Contaminants and Their Degradation
Products
The position of reactive nanoparticles within the aquifer can also be deduced
indirectly from measuring the levels of target contaminants and/or their degradation
products. It is possible to monitor the total concentration of the target contaminant as
well as its speciation (e.g., oxidation states of metals). In the case of chlorinated
hydrocarbons (CHCs), particular pollutants as well as their sum can be measured.
Concentration of volatile organic compounds (VOCs, common pollutants treated by
nZVI) can be determined directly at the site using membrane interface probe—MIP
(find more in Chap. 31). Nevertheless, much more common protocol involves
groundwater sampling and its subsequent analysis in a laboratory employing gas
chromatography–mass spectrometry (GC-MS, Fig. 33.8). Therefore, special
640
P. Skácelová and J. Filip