the substrate owing to its successful application in locality 1 in order to support
microbial populations. Whey was applied using a circulation system; the substrate
was mixed with groundwater from downgradient monitoring wells (HS-1 and HS-2)
and then injected back to the injection wells (IN-1 A and IN-2 A) at a rate of
0.5–0.7 L/s. During the biotic phase, 8.3 m
3 of whey was applied in total in a dosing
ratio of 1/50 (substrate/groundwater). After the application period (five weeks) the
circulation of groundwater continued for nine days and therefore the natural groundwater flow was reestablished and the locality was monitored for another five months.
20.3.3 Monitoring of Physicochemical Parameters and Levels
of Contamination
Similarly to the pilot test in locality 1, the drop in the oxidation-reduction
(to À400 mV) potential was observed after the first injection of nZVI. A less
significant decrease in E h was also observed after the second nZVI injection and
the substrate application. Finally, the oxidation-reduction potential was stabilized at
50 mV and 100 mV in the first and second monitoring line, respectively. The drop of
the E h supported by the analysis of inorganics documents the course of reducing
conditions in the monitoring wells during the whole remediation experiment including the biotic phase.
The first injection of nZVI resulted in a decrease of the Cr(VI) concentration
(below the detection limits) in the first monitoring line, but the concentrations started
to rebound within several weeks. After the second injection, the level of chromium
contamination reached only 10–15% of the initial concentrations. The reductive
effect of nZVI in the second monitoring line was less pronounced. However, the
final Cr(VI) removal was achieved by the second phase. After addition of the
microbial substrate, the concentration of Cr(VI) decreased below the analytical
limits of detection in a very short time and lasted for the whole monitoring period,
even after 188 days from the whey application, shown in Fig. 20.3. In addition, the
laboratory studies showed that the concentration of total chromium in the soil
samples corresponded to the initial concentration of Cr(VI), which documents
fixation of Cr(III) in the soil matrix.
Transformation of chlorinated ethenes by nZVI even after the second injection
was not observed in the monitoring wells. The authors attributed the limited degradation efficiency during the first phase to the competition with Cr(VI), which is a
thermodynamically more favored reducible compound. However, the addition of the
organic substrate resulted in a rapid decrease of parent trichloroethene (TCE) below
the limit of detection together with a temporal increase and a further decrease of its
transformation products—less chlorinated and dechlorinated ethenes. The concentration of parent TCE remained below the detection limit for the rest of the monitoring period (six months) in the first monitoring line. In the second monitoring line,
36–97% removal of chlorinated ethenes was achieved at the end of the pilot test.
20 Nano-Bioremediation: Nanoscale Zero-Valent Iron for Inorganic and. . .
431
microbial populations. Whey was applied using a circulation system; the substrate
was mixed with groundwater from downgradient monitoring wells (HS-1 and HS-2)
and then injected back to the injection wells (IN-1 A and IN-2 A) at a rate of
0.5–0.7 L/s. During the biotic phase, 8.3 m
3 of whey was applied in total in a dosing
ratio of 1/50 (substrate/groundwater). After the application period (five weeks) the
circulation of groundwater continued for nine days and therefore the natural groundwater flow was reestablished and the locality was monitored for another five months.
20.3.3 Monitoring of Physicochemical Parameters and Levels
of Contamination
Similarly to the pilot test in locality 1, the drop in the oxidation-reduction
(to À400 mV) potential was observed after the first injection of nZVI. A less
significant decrease in E h was also observed after the second nZVI injection and
the substrate application. Finally, the oxidation-reduction potential was stabilized at
50 mV and 100 mV in the first and second monitoring line, respectively. The drop of
the E h supported by the analysis of inorganics documents the course of reducing
conditions in the monitoring wells during the whole remediation experiment including the biotic phase.
The first injection of nZVI resulted in a decrease of the Cr(VI) concentration
(below the detection limits) in the first monitoring line, but the concentrations started
to rebound within several weeks. After the second injection, the level of chromium
contamination reached only 10–15% of the initial concentrations. The reductive
effect of nZVI in the second monitoring line was less pronounced. However, the
final Cr(VI) removal was achieved by the second phase. After addition of the
microbial substrate, the concentration of Cr(VI) decreased below the analytical
limits of detection in a very short time and lasted for the whole monitoring period,
even after 188 days from the whey application, shown in Fig. 20.3. In addition, the
laboratory studies showed that the concentration of total chromium in the soil
samples corresponded to the initial concentration of Cr(VI), which documents
fixation of Cr(III) in the soil matrix.
Transformation of chlorinated ethenes by nZVI even after the second injection
was not observed in the monitoring wells. The authors attributed the limited degradation efficiency during the first phase to the competition with Cr(VI), which is a
thermodynamically more favored reducible compound. However, the addition of the
organic substrate resulted in a rapid decrease of parent trichloroethene (TCE) below
the limit of detection together with a temporal increase and a further decrease of its
transformation products—less chlorinated and dechlorinated ethenes. The concentration of parent TCE remained below the detection limit for the rest of the monitoring period (six months) in the first monitoring line. In the second monitoring line,
36–97% removal of chlorinated ethenes was achieved at the end of the pilot test.
20 Nano-Bioremediation: Nanoscale Zero-Valent Iron for Inorganic and. . .
431