oxidation of aniline. Zero removal efficiency in Fig. 14.6 means that no changes in
the concentrations of selected contaminants were observed during the pilot test,
especially in the case of blank: xylenes, cresols, chlorophenols, dichlorophenols,
nitrobenzene.
Based on the obtained results of the pilot-field application, the combination of the
two oxidizing agents seems to be a promising way for quick removal of a wide range
of organic contaminants. It can not only be used for groundwater remediation but
also for wastewater and other types of water purification by ex situ methods.
Although ferrates used independently in model solutions exhibit strong oxidative
effects, they rapidly deteriorate without noticeable effects on chemically stable
contaminants in highly polluted real waters. The efficiency of the reaction can be
increased by addition of hydrogen peroxide to the formed ferric sludge. The properties of the two reagents can therefore be combined—efficiency of ferrates alone
(oxidation, coagulation) and subsequently efficiency of radical oxidation, which is
initiated after the addition of hydrogen peroxide to ferric sludge. In this specific case,
the formed sludge acts most likely as a catalyst for radical degradation of hydrogen
peroxide. Therefore, the removal efficiency is comparable to the Fenton oxidation.
On top of that, ferrates utilization does not lead to increased salinity of water and no
other substances are introduced to an aqueous environment (as sulfates, acids, etc.).
From the viewpoint of the environmental protection, the proposed combination
represents no risk—ferrates are reduced to Fe
3+ /Fe
2+ and precipitate in the form of
polyhydroxy complexes and hydroxides, which commonly occur in nature, and
hydrogen peroxide is degraded to O 2 and H 2 O.
14.3.3 Results of Pilot In Situ Application
The purpose of this type of ferrate application was to verify the results obtained from the
laboratory experiment employing the method of in situ remediation. It is necessary to
emphasize that the pH was adjusted only before the first application round; in another
application round, only H 2 O 2 was added into the application borehole. The reason for
this step was to verify if the remaining ferric sludge, which was detected in the borehole
even during the second and the third application round, would react with a new dose of
hydrogen peroxide even without pH adjustment. After all applications of hydrogen
peroxide, the reaction in the borehole was relatively tempestuous, but it lasted only a few
hours. Between all application rounds, regular monitoring was carried out. In the
following graphs (Fig. 14.7a–c) physicochemical parameters are shown. It is obvious
that rapid increase in the E h and dissolved oxygen (DO) was observed after the
application in all cases, as a consequence of H 2 O 2 decomposition. Decrease in the pH
was also observed in all cases. In the first application round it was the consequence of
target pH adjustment. In other application rounds, when the pH was not adjusted, it was
the result of acidic nature of H 2 O 2 itself.
According to the graph showing CE contamination development (Fig. 14.7d), it is
obvious that a rapid decrease was observed after each application. It made no
14 Field Study V: Combined Oxidation Technology Using Ferrates (Fe
IV–VI
). . .
327
the concentrations of selected contaminants were observed during the pilot test,
especially in the case of blank: xylenes, cresols, chlorophenols, dichlorophenols,
nitrobenzene.
Based on the obtained results of the pilot-field application, the combination of the
two oxidizing agents seems to be a promising way for quick removal of a wide range
of organic contaminants. It can not only be used for groundwater remediation but
also for wastewater and other types of water purification by ex situ methods.
Although ferrates used independently in model solutions exhibit strong oxidative
effects, they rapidly deteriorate without noticeable effects on chemically stable
contaminants in highly polluted real waters. The efficiency of the reaction can be
increased by addition of hydrogen peroxide to the formed ferric sludge. The properties of the two reagents can therefore be combined—efficiency of ferrates alone
(oxidation, coagulation) and subsequently efficiency of radical oxidation, which is
initiated after the addition of hydrogen peroxide to ferric sludge. In this specific case,
the formed sludge acts most likely as a catalyst for radical degradation of hydrogen
peroxide. Therefore, the removal efficiency is comparable to the Fenton oxidation.
On top of that, ferrates utilization does not lead to increased salinity of water and no
other substances are introduced to an aqueous environment (as sulfates, acids, etc.).
From the viewpoint of the environmental protection, the proposed combination
represents no risk—ferrates are reduced to Fe
3+ /Fe
2+ and precipitate in the form of
polyhydroxy complexes and hydroxides, which commonly occur in nature, and
hydrogen peroxide is degraded to O 2 and H 2 O.
14.3.3 Results of Pilot In Situ Application
The purpose of this type of ferrate application was to verify the results obtained from the
laboratory experiment employing the method of in situ remediation. It is necessary to
emphasize that the pH was adjusted only before the first application round; in another
application round, only H 2 O 2 was added into the application borehole. The reason for
this step was to verify if the remaining ferric sludge, which was detected in the borehole
even during the second and the third application round, would react with a new dose of
hydrogen peroxide even without pH adjustment. After all applications of hydrogen
peroxide, the reaction in the borehole was relatively tempestuous, but it lasted only a few
hours. Between all application rounds, regular monitoring was carried out. In the
following graphs (Fig. 14.7a–c) physicochemical parameters are shown. It is obvious
that rapid increase in the E h and dissolved oxygen (DO) was observed after the
application in all cases, as a consequence of H 2 O 2 decomposition. Decrease in the pH
was also observed in all cases. In the first application round it was the consequence of
target pH adjustment. In other application rounds, when the pH was not adjusted, it was
the result of acidic nature of H 2 O 2 itself.
According to the graph showing CE contamination development (Fig. 14.7d), it is
obvious that a rapid decrease was observed after each application. It made no
14 Field Study V: Combined Oxidation Technology Using Ferrates (Fe
IV–VI
). . .
327