12 Chlorophenols Dechlorination Water Treatment Using …
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surface, or (3) formation of passive oxides blocking the ZVI reactive surfaces. Less
hydrogen gas formation with the Ni/Fe (Fig. 12.6) is consistent with the lower/partial
CP degradation observed using this system (Fig. 12.1).
The rate of hydrogen gas formation may vary depending on the characteristics of
the ZVI surface as well as the electron acceptors present in the systems. However,
the results showed that the rate of hydrogen gas accumulation with each CP was
approximately the same with some fluctuations observed with 2,4-DCP and seems
to be independent of the type of CP present in the system (Fig. 12.6).
The solution pH was measured at each sampling time with Ni/Fe and each CPs
and the data is presented in Fig. 12.6b. In general, an increase in the solution pH was
observed over the reaction duration. An increase in pH from 5.6 or 6.1 to 6.1 or 7.1
was noted during the initial reaction period (1–2 days) followed by a pH decrease over
the remaining duration of the experiment. After 25 days of reaction, the pH levels
between 6.3 and 6.9 were observed with all treatments (Fig. 12.6b). An increase
in solution pH occurs due to a consumption of protons during CP dechlorination
and production of hydroxide ions during metal corrosion. In addition, some studies
attributed the change in solution pH to the accumulation of daughter compounds with
different acid dissociation constants during the degradation of parent CP compound
using zero-valent metals (Kim 1999; Liu et al. 2001). Previous studies also have
reported an increase in solution pH during interaction of CPs with ZVI and/or ZVIbased bimetals (Choi et al. 2008; Kim and Carraway 2000; Liu et al. 2001; Wei et al.
2006).
12.3.4 Incorporation of Chlorophenols onto Ni/Fe Solid
Phase and Iron Oxides
Removal of the tested CPs from solution with Ni/Fe occurred due to concurrent
dechlorination and incorporation. The amount of extractable CP incorporated per unit
mass of Ni/Fe (C s , µmole CP/g of Ni/Fe) was calculated in each system as follows: C S
= [(C T − C W ) *V W )]/M Ni/Fe , where C T = total system CP concentration [µmole/l];
C W = aqueous phase CP concentration [µmole/l]; V W = volume of aqueous solution
[l]; and M Ni/Fe = initial amount of Ni/Fe used in the batch reactor [g]. The amounts
of extractable CP incorporated in the Ni/Fe solid phase are presented in Fig. 12.7.
A rapid increment in the amount of incorporated CPs was observed during
the initial reaction period up to 5 days (Fig. 12.7), which could be due to sorption of CPs on to the reactive and/or non-reactive sites of Ni/Fe particles and/or
physical entrapment/co-precipitation of CPs with the iron oxides (Noubactep 2009;
Noubactep 2008). In addition, the compounds present in the Ni/Fe bimetallic-water
system as well as the iron oxide phases forming on the Ni/Fe surface subject to
continuous change, thus could affect the amount of CPs incorporated with the oxide
phases during the reaction period. Approximately constant levels of incorporated
and extracted CP concentration demonstrated by some CPs at the later stages of the
289
surface, or (3) formation of passive oxides blocking the ZVI reactive surfaces. Less
hydrogen gas formation with the Ni/Fe (Fig. 12.6) is consistent with the lower/partial
CP degradation observed using this system (Fig. 12.1).
The rate of hydrogen gas formation may vary depending on the characteristics of
the ZVI surface as well as the electron acceptors present in the systems. However,
the results showed that the rate of hydrogen gas accumulation with each CP was
approximately the same with some fluctuations observed with 2,4-DCP and seems
to be independent of the type of CP present in the system (Fig. 12.6).
The solution pH was measured at each sampling time with Ni/Fe and each CPs
and the data is presented in Fig. 12.6b. In general, an increase in the solution pH was
observed over the reaction duration. An increase in pH from 5.6 or 6.1 to 6.1 or 7.1
was noted during the initial reaction period (1–2 days) followed by a pH decrease over
the remaining duration of the experiment. After 25 days of reaction, the pH levels
between 6.3 and 6.9 were observed with all treatments (Fig. 12.6b). An increase
in solution pH occurs due to a consumption of protons during CP dechlorination
and production of hydroxide ions during metal corrosion. In addition, some studies
attributed the change in solution pH to the accumulation of daughter compounds with
different acid dissociation constants during the degradation of parent CP compound
using zero-valent metals (Kim 1999; Liu et al. 2001). Previous studies also have
reported an increase in solution pH during interaction of CPs with ZVI and/or ZVIbased bimetals (Choi et al. 2008; Kim and Carraway 2000; Liu et al. 2001; Wei et al.
2006).
12.3.4 Incorporation of Chlorophenols onto Ni/Fe Solid
Phase and Iron Oxides
Removal of the tested CPs from solution with Ni/Fe occurred due to concurrent
dechlorination and incorporation. The amount of extractable CP incorporated per unit
mass of Ni/Fe (C s , µmole CP/g of Ni/Fe) was calculated in each system as follows: C S
= [(C T − C W ) *V W )]/M Ni/Fe , where C T = total system CP concentration [µmole/l];
C W = aqueous phase CP concentration [µmole/l]; V W = volume of aqueous solution
[l]; and M Ni/Fe = initial amount of Ni/Fe used in the batch reactor [g]. The amounts
of extractable CP incorporated in the Ni/Fe solid phase are presented in Fig. 12.7.
A rapid increment in the amount of incorporated CPs was observed during
the initial reaction period up to 5 days (Fig. 12.7), which could be due to sorption of CPs on to the reactive and/or non-reactive sites of Ni/Fe particles and/or
physical entrapment/co-precipitation of CPs with the iron oxides (Noubactep 2009;
Noubactep 2008). In addition, the compounds present in the Ni/Fe bimetallic-water
system as well as the iron oxide phases forming on the Ni/Fe surface subject to
continuous change, thus could affect the amount of CPs incorporated with the oxide
phases during the reaction period. Approximately constant levels of incorporated
and extracted CP concentration demonstrated by some CPs at the later stages of the