or NO 3
À . In a suboxic environment, it is MnO 2 or Fe(OH) 3 , and in a reducing
environment it is SO 4
2À or CO 2 (Fig. 1.3).
1.7 The Principle of Remedial Reduction Technologies
For reduction methods, reagents that easily release electrons are used as a reduction
agent, thus adjusting the conditions in the groundwater on the lower limit of water
stability or even below it (Fig. 1.1). If there are substances that are capable of
accepting electrons in the system, oxidation-reduction processes are then in progress.
The most commonly used reagents are sodium dithionites (Na 2 S 2 O 4 ) (Chung 1981),
calcium polysulfide (CaS x ) (Wazne et al. 2007), sodium metabisulfite (Na 2 S 2 O 5 )
(Chang 2003), sodium hydrosulfide (NaHS), sodium sulfite (Na 2 SO 3 ) (Bianco
Prevot et al. 2018), ferrous sulfate (Fe 2 SO 4 ) (Mončeková et al. 2016), and currently
metallic elements (zero-valent), namely Fe
0 (Tosco et al. 2014) iron, in the form of
chips or nanoparticles. In addition, organic waste from food production, e.g., whey,
which contains the anion of lactic acid (CH 3 CH(OH)COO
À ), can be biologically
degraded to CO 2 with the release of electrons. The reaction is similar to the general
degradation of organic compounds caused by oxygen, which is the opposite of
photosynthesis expressed by Eq. (1.1). The oxidation reaction for the abovementioned reducing agents can be expressed by the following equations
Fig. 1.3 Redox ladder of sequential oxidation of species in natural waters
12
M. Černík and J. Zeman
À . In a suboxic environment, it is MnO 2 or Fe(OH) 3 , and in a reducing
environment it is SO 4
2À or CO 2 (Fig. 1.3).
1.7 The Principle of Remedial Reduction Technologies
For reduction methods, reagents that easily release electrons are used as a reduction
agent, thus adjusting the conditions in the groundwater on the lower limit of water
stability or even below it (Fig. 1.1). If there are substances that are capable of
accepting electrons in the system, oxidation-reduction processes are then in progress.
The most commonly used reagents are sodium dithionites (Na 2 S 2 O 4 ) (Chung 1981),
calcium polysulfide (CaS x ) (Wazne et al. 2007), sodium metabisulfite (Na 2 S 2 O 5 )
(Chang 2003), sodium hydrosulfide (NaHS), sodium sulfite (Na 2 SO 3 ) (Bianco
Prevot et al. 2018), ferrous sulfate (Fe 2 SO 4 ) (Mončeková et al. 2016), and currently
metallic elements (zero-valent), namely Fe
0 (Tosco et al. 2014) iron, in the form of
chips or nanoparticles. In addition, organic waste from food production, e.g., whey,
which contains the anion of lactic acid (CH 3 CH(OH)COO
À ), can be biologically
degraded to CO 2 with the release of electrons. The reaction is similar to the general
degradation of organic compounds caused by oxygen, which is the opposite of
photosynthesis expressed by Eq. (1.1). The oxidation reaction for the abovementioned reducing agents can be expressed by the following equations
Fig. 1.3 Redox ladder of sequential oxidation of species in natural waters
12
M. Černík and J. Zeman