Environmental Engineering Reference
In-Depth Information
6. Organic compounds including Methyl
tert
-butyl Ether (MTBE) [87], aromatics (e.g., BTEX) [88-91]), hydrocarbons
[21, 92-98], hormonal pollutants [99]. Metal carbonyl pollutants (e.g., Fe(CO)
5
, Fe(CO)
4
) can be reduced to n-Fe
0
(5-15 nm) by thermolysis in the presence of functional polymers [100].
7. Most metals, metalloids, and nonmetals, including their oxides, hydrides, hydroxides, peroxides, nitrates, nitrites,
sulfides, sulfates, halides, carbonates, bicarbonates, and phosphates. ZVM is used to adjust the Eh and pH. This
shifts the water redox environment into a redox environment, which will allow either direct precipitation, or
precipitation by substitution of Fe in a precipitated Fe corrosion product [10, 101-113]. Examples of contaminant
ions and the associated precipitated products, which can be formed by the presence of ZVM, are summarized in
Appendix 1.B.
8. Microbiota [10, 114-128] including
Escherichia coli
[115-118, 123, 124, 128], colliforms (e.g.,
Enterococcus faecium
,
Enterococcus faecilis
) [128],
Klebsiella pneumoniae
[125],
Salmonella typhimurium
[10]
, Salmonella enterica
[124],
Salmonella paratyphi
[125]
, Shigella
spp. [125],
Salmonella
spp.[124],
Staphylococcus aureus
[117, 118],
Streptococci
spp. [126],
Bacillus cereuis
[118],
Bacillus subtilis var. niger
[116, 119, 123],
Dehalococcoides
spp. [123],
Pseudomonas
spp.
[118],
Pseudomonas fluorescens
[116, 118, 123],
Pseudomonas aeruginosa
[125],
Vibrio parahaemolyticus
[118],
Vibrio cholerae
[126], phiX174/FX174 [120, 128], T1 [121], Aichi virus [120], adenovirus 41 [120], MS-2 [116, 120,
128], Hepatitis A [122], norovirus [122], rotavirus [122], f2 virus [128],
Alcaligenes eutrophus
[123],
Aspergillus versi-
color
[116, 119, 122],
Cryptosporidium
spp. [126],
Naeglaeria
spp. [126]
, Naeglaeria fowleri
[128],
Giardia
spp. [126],
Hartmannella veriformis
[128],
Tetrahymena pyriformis
[128],
Daphnia magna
[116],
Pseudokirchneriella subcapitata
[116],
Dunaliella tertiolecta
[116],
Thalassiorsria pseudonana
[116],
Isochrysis galbbana
[116], fungi [127], prions
[127], viruses [127], protozoa [127], bacteria [127], algae [127], etc. n-Fe
0
(20-30 nm) rapidly inactivates microorgan-
isms by coating them with Fe(OOH) [119]. Inactivation is by one or more of Eh:pH changes and the interaction of Fe
corrosion products (oxides, hydroxides, and peroxides), for example, [114, 119].
9. Macrobiota. n-Fe
0
in soil (0.1 to >1 g n-Fe
0
kg
−1
soil) adversely affect worms (e.g.,
Eisenia fetida
and
Lumbricus rubellus
)
and springtails (e.g.,
Folsomnia candida
) [123].
10. Plants. Concentrations of n-Fe
0
in excess of 250 mg kg
−1
soil have been found to stunt the growth of rye grass and
clover [123].
1.3
remediation mecHanisms
The mechanisms associated with ZVM remediation are the subject of conflicting, overlapping, and competing hypotheses, and
more than one mechanism applies in each remediation environment. The principal hypotheses are
1.
Catalyst Model:
ZVM acts as a Langmuir-Hinshelwood catalyst (e.g., [55, 95], that is, adsorption of reactants on ZVM
surface and desorption of products [55, 130, 131]), or Eley-Rideal catalyst (e.g., [95, 129], i.e., adsorption of one or more
reactants on the ZVM surface with reaction of the adsorbed species with one or more fluid-phase reactants that are not
adsorbed on the ZVM surface to produce a product [129-131]), or acid catalyst (Fe-H
n
+
) [10, 21, 96-98].
2.
Redox Model:
ZVM changes the water Eh and pH, thereby forcing remediation by changing both K and ΔG for the reme-
diation reaction [10]. Under this model, n-ZVM reactions are essentially fluid phase electrochemical reactions, or contact
surface reactions [10].
3.
Galvanic Model:
ZVM ionization (Appendix 1.B, Appendix 1.C) results in n-ZVM acting as self-charging galvanic
cells (Fig. 1.2) that adjust the water pH and Eh. This adjustment forces a change in the cation:anion equilibrium
state within the water [10]. The change in equilibrium state forces the reduction/oxidation of specific cations and
anions, and a change in the Gibbs Free Energy associated with the remediation reaction [103, 104]. The presence of
ZVM (and ZVM-ion adducts) in water creates (in a diabatic environment) a perpetual oscillation between higher
and lower Eh and higher and lower pH [10] (Fig. 1.1b-j). This oscillation, which can be interpreted as alternating
charging and discharging of the galvanic cells (Fig. 1.2): (i) creates, discharges, and adsorbs H
+
(protons, H
3
O
+
,
H
5
O
2
+
, H
7
O
3
+
, H
9
O
4
+
, FeH
2+
, FeH
2
+
), e
−
(H
−
, H
2
O
−
, electrons), O
−
, O
2−
, O
2
−
, H
2
O
2
, OH, OH
−
, O
2
H, and O
2
H
−
; (ii) cre-
ates a unique (ZVM specific) trajectory of Eh/pH change with both residence time and space velocity [10]. This
galvanic discharge-recharge mechanism results in substantial water consumption (>0.18
t
H
2
O
t
−1
n-Fe
0
), but drives
fluid phase (and ZVM/ion surface) Fenton Reactions, electron shuttle reactions, proton shuttle reactions, and oxide
(H
x
O
y
(
c
+/−)
) shuttle reactions within water [10, 96]. These reactions undertake the reduction/oxidation of pollutants,
