Environmental Engineering Reference
In-Depth Information
4.1 Introduction
The development of remediation technology of soil and groundwater contaminated with
priority pollutants, including chlorinated compounds, inorganic ions, and heavy met-
als, has recently received much attention [1-6]. However, the contamination of soil and
groundwater is enormous and dificult to clean up because of the inherent complex-
ity of the soil and groundwater properties [7]. Several technologies, such as perme-
able reactive barriers (PRBs),
in situ
bioremediation, and air sparging have been applied
for the remediation of contaminated soils and groundwater. Laboratory-scale and ield
studies have demonstrated that PRBs packed with zerovalent metals (ZVMs) such as
Fe, Cu, Al, Si, Zn, and Mg have been shown to be a promising strategy for the removal
of organic and inorganic pollutants in contaminated subsurface environments [8-10].
Table 4.1 shows the reduction of priority pollutants by ZVMs under anaerobic condi-
tions. Many halogenated hydrocarbons, including carbon tetrachloride (CT), tetrachlo-
roethylene (PCE), and trichloroethylene (TCE), can be reductively degraded by ZVMs
[9,11-13]. Of various materials used, zerovalent iron (ZVI) and bimetallic iron systems
are the most often used materials because of their suitable redox potential for the reduc-
tion of halogenated compounds, no obvious toxic effect, and abundance in the earth's
crust.
ZVI is a moderate reducing agent with relatively low redox potential (
V
= −0.44 V vs. SHE
at 25°C). ZVI can react with dissolved oxygen (DO) and/or water to form ferric oxides. In
the early 1990s, Gillham and coworkers found that ZVI has an excellent ability in dechlo-
rination of chlorinated hydrocarbons under anaerobic conditions [14,15]. It is quickly rec-
ognized that the reduction of organic compounds by metal iron is a well-known classic
electrochemical/corrosion process to both organic chemists and corrosion scientists. Much
of the emphasis on the use of ZVI for the decomposition of priority pollutants came from
the work of Matheson and Tratynek [16], who proposed the major pathways for reductive
dechlorination in an anoxic Fe
0
-H
2
O system. On the basis of the relation of redox potential
TABLE 4.1
Reduction of Priority
Pollutants by ZVM under Anaerobic Conditions
Metal
pH
Target Compound
k
obs
(h
−1
)
Products
References
Fe
5-8
TCE
0.165
cis
-DCE, 1,1-DCE, VC
[53-56]
Neutral pH
PCE
0.025
TCE,
cis
-DCE, 1,1-DCE
[57-59]
CT
0.19-0.41
CF
[60]
5.5
Nitrate
0.059-0.34
Ammonia
[61-63]
7
Pentachlorophenol
0.0039
Tetrachlorophenol
[64]
Si
8.3
PCE
0.0034
TCE
[44]
8.3
CT
0.34
CF
[44]
Mg
4-Chlorophenol
0.23
Chlorophenol
[50]
Endosulfan
10.5
Bicyclo(2,2,1)hepta(2,5)diene
Zn
7.0
CT
2.29
CF
[65]
7.0
CF
0.398
DCM
[65]
Al
4<, 11>
4-Chlorophenol
0.46
1,4-Biphenol
[47,48]
