temperature fluctuations were inside Æ0.5
C interval. However, after the DC was
switched on, an increase in the temperature of up to 2.5
C was recorded in both
aquifers. Moreover, the temperature increase is proportional to the electric power.
During the first year, the temperature increased by about 2
C compared with the
surrounding aquifers, but then the first stagnation was observed, as a result of a
decrease in the electric power of the oxidized anodes. After the anode was replaced,
the current increased and consequently the temperature rose up to 2.5
C. To keep
such an elevated temperature in a flowing aquifer is difficult; with another anode
oxidation the temperature difference decreased. Again, the anode replacement
increased the differences to about 2.5
C, with a local maximum of 3.5
C in a
Quaternary aquifer in a winter period. The anode destruction caused a temperature
decrease again and it remained until the end of the experiment.
4.3.2.1 Evaluation of the pH Course
Well IS4 monitors the situation in the middle of the electrode lines. During the whole
monitoring period, the pH value ranged between 7 and 8 independently of the
installed technologies (Fig. 4.16). In the area of the cathode (IS4-CAT), the pH
was strongly dependent on the DC field causing a reduction in the water and thus the
formation of OH
À ions. During the initial period of approximately 6 weeks, there
was a gradual increase in the pH up to a value greater than 12.5, where the pH
stabilized and was not affected by the gradual degradation of the anodes. In M35,
i.e., 10 months after the DC field was connected, there was a sudden decrease in the
pH due to anode dysfunction. After the anodes were replaced, there was again a rapid
increase in the pH back to a constant value of approximately 12.5. This process was
repeated during the whole pilot test.
6
7
8
9
10
11
12
13
Eh (mV)
pH (-)
pH IS4
pH IS4-CAT
TODA
TODA
NF 25S
NF 25S
DC on
New anodes
New anodes
New anodes
DC off
Eh IS4
Eh IS4-CAT
time (months)
M0
M10
M20
M30
M40
M50
M60
600
400
200
0
-200
-400
-600
-800
Fig. 4.16 Development of pH and E h in the test polygon
4 Combination of Electrokinetics and nZVI Remediation
81
C interval. However, after the DC was
switched on, an increase in the temperature of up to 2.5
C was recorded in both
aquifers. Moreover, the temperature increase is proportional to the electric power.
During the first year, the temperature increased by about 2
C compared with the
surrounding aquifers, but then the first stagnation was observed, as a result of a
decrease in the electric power of the oxidized anodes. After the anode was replaced,
the current increased and consequently the temperature rose up to 2.5
C. To keep
such an elevated temperature in a flowing aquifer is difficult; with another anode
oxidation the temperature difference decreased. Again, the anode replacement
increased the differences to about 2.5
C, with a local maximum of 3.5
C in a
Quaternary aquifer in a winter period. The anode destruction caused a temperature
decrease again and it remained until the end of the experiment.
4.3.2.1 Evaluation of the pH Course
Well IS4 monitors the situation in the middle of the electrode lines. During the whole
monitoring period, the pH value ranged between 7 and 8 independently of the
installed technologies (Fig. 4.16). In the area of the cathode (IS4-CAT), the pH
was strongly dependent on the DC field causing a reduction in the water and thus the
formation of OH
À ions. During the initial period of approximately 6 weeks, there
was a gradual increase in the pH up to a value greater than 12.5, where the pH
stabilized and was not affected by the gradual degradation of the anodes. In M35,
i.e., 10 months after the DC field was connected, there was a sudden decrease in the
pH due to anode dysfunction. After the anodes were replaced, there was again a rapid
increase in the pH back to a constant value of approximately 12.5. This process was
repeated during the whole pilot test.
6
7
8
9
10
11
12
13
Eh (mV)
pH (-)
pH IS4
pH IS4-CAT
TODA
TODA
NF 25S
NF 25S
DC on
New anodes
New anodes
New anodes
DC off
Eh IS4
Eh IS4-CAT
time (months)
M0
M10
M20
M30
M40
M50
M60
600
400
200
0
-200
-400
-600
-800
Fig. 4.16 Development of pH and E h in the test polygon
4 Combination of Electrokinetics and nZVI Remediation
81