12 Chlorophenols Dechlorination Water Treatment Using …
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the Raman analysis, of all Ni/Fe samples reacted with CPs, it was observed that the
spectra of different iron oxides present overlapped extensively, which indicated the
presence of a mixture of oxide phases. The presence of a mixture of oxide phases made
it complex for clear identification of individual oxide phases in the observed spectra. Therefore, multivariate curve resolution with alternating least squares (MCRALS) within MATLAB (Mathworks
® ) was used for quantification of specific iron
oxides (Jaumot et al. 2005). The green rust oxides were excluded and not considered
for the group of reference spectra, as they are reported as unstable and subject to
transformation to other oxides under the conditions used in the present study.
The effect of Ni/Fe treatment on the concentration of different CPs degraded
after 25 days reaction period was compared using statistical analysis (one-way and
two-way analysis of variance) and SPSS statistical software (IBM SPSS Statistics
version 20.0.0 [SPSS Inc., USA]). The effect of Ni/Fe treatment on the amount of CP
degraded, levels of extractable CPs incorporated as well as H 2 gas accumulated after
25 days reaction were compared. The differences were considered as significant at
95% confidence level.
12.3 Results and Discussion
12.3.1 Dechlorination of Chlorophenols Using Ni/Fe
The degradation of four CPs (PCP, 2,3,4,6-TeCP, 2,4,6-TCP, 2,4-DCP) using Ni/Fe
and the subsequent formation of daughter compounds is presented in Fig. 12.1. After
25-day reaction period, the CPs reactivity with Ni/Fe in the order of highest to lowest
was: PCP > 2,3,4,6-TeCP > 2,4,6-TCP ≈ 2,4-DCP (Fig. 12.1). After 25 days reaction,
approximately 55% of PCP, 46% of 2,3,4,6-TeCP, 34% of 2,4,6-TCP, and 30% of 2,4DCP, which was initially introduced to each system, were removed from the aqueous
phase (Fig. 12.1). Among the four CPs tested, PCP showed a significantly higher
amount of dechlorination (p < 0.05), whereas 2,4,6-TCP showed a significantly lower
amount of dechlorination (p < 0.05) after 25 days of reaction with Ni/Fe.
Dechlorination of PCP and 2,3,4,6-TeCP using Ni/Fe resulted in accumulation of
CPs with a lower degree of chlorination, with trace amounts of phenol being detected
(Fig. 12.1b, c).
The CPs with a lower degree of chlorination continuously forming and accumulating in the system during the reaction of PCP or TeCP with Ni/Fe bimetal (Fig. 12.1b,
c) can create a competition for the same electrons and reactive sites on the Ni/Fe
and ZVI surfaces for dechlorination. Hence, the formation and gradual accumulation
of CPs with a lower degree of chlorination may create adverse impacts on the rate
of dechlorination of PCP or TeCP by Ni/Fe. Such a competitive effect between the
parent CP and daughter CPs (with a lower degree of chlorination) can lead to partial
dechlorination of PCP or TeCP. On the other hand, when 2,4,6-TCP was reacted with
Ni/Fe, small concentrations of DCPs and monochlorophenols (MCPs) were observed
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the Raman analysis, of all Ni/Fe samples reacted with CPs, it was observed that the
spectra of different iron oxides present overlapped extensively, which indicated the
presence of a mixture of oxide phases. The presence of a mixture of oxide phases made
it complex for clear identification of individual oxide phases in the observed spectra. Therefore, multivariate curve resolution with alternating least squares (MCRALS) within MATLAB (Mathworks
® ) was used for quantification of specific iron
oxides (Jaumot et al. 2005). The green rust oxides were excluded and not considered
for the group of reference spectra, as they are reported as unstable and subject to
transformation to other oxides under the conditions used in the present study.
The effect of Ni/Fe treatment on the concentration of different CPs degraded
after 25 days reaction period was compared using statistical analysis (one-way and
two-way analysis of variance) and SPSS statistical software (IBM SPSS Statistics
version 20.0.0 [SPSS Inc., USA]). The effect of Ni/Fe treatment on the amount of CP
degraded, levels of extractable CPs incorporated as well as H 2 gas accumulated after
25 days reaction were compared. The differences were considered as significant at
95% confidence level.
12.3 Results and Discussion
12.3.1 Dechlorination of Chlorophenols Using Ni/Fe
The degradation of four CPs (PCP, 2,3,4,6-TeCP, 2,4,6-TCP, 2,4-DCP) using Ni/Fe
and the subsequent formation of daughter compounds is presented in Fig. 12.1. After
25-day reaction period, the CPs reactivity with Ni/Fe in the order of highest to lowest
was: PCP > 2,3,4,6-TeCP > 2,4,6-TCP ≈ 2,4-DCP (Fig. 12.1). After 25 days reaction,
approximately 55% of PCP, 46% of 2,3,4,6-TeCP, 34% of 2,4,6-TCP, and 30% of 2,4DCP, which was initially introduced to each system, were removed from the aqueous
phase (Fig. 12.1). Among the four CPs tested, PCP showed a significantly higher
amount of dechlorination (p < 0.05), whereas 2,4,6-TCP showed a significantly lower
amount of dechlorination (p < 0.05) after 25 days of reaction with Ni/Fe.
Dechlorination of PCP and 2,3,4,6-TeCP using Ni/Fe resulted in accumulation of
CPs with a lower degree of chlorination, with trace amounts of phenol being detected
(Fig. 12.1b, c).
The CPs with a lower degree of chlorination continuously forming and accumulating in the system during the reaction of PCP or TeCP with Ni/Fe bimetal (Fig. 12.1b,
c) can create a competition for the same electrons and reactive sites on the Ni/Fe
and ZVI surfaces for dechlorination. Hence, the formation and gradual accumulation
of CPs with a lower degree of chlorination may create adverse impacts on the rate
of dechlorination of PCP or TeCP by Ni/Fe. Such a competitive effect between the
parent CP and daughter CPs (with a lower degree of chlorination) can lead to partial
dechlorination of PCP or TeCP. On the other hand, when 2,4,6-TCP was reacted with
Ni/Fe, small concentrations of DCPs and monochlorophenols (MCPs) were observed