Environmental Engineering Reference
In-Depth Information
1.4
remediation market
Contaminated sites (soils and groundwater) vary in size from <100 m
2
to >10 km
2
. The number of contaminated sites, which
could benefit from n-ZVM treatment, is estimated at 350,000-400,000 in Europe, 235,000-355,000 in the United States [136,
162]. There are probably a similar number of contaminated sites in Canada, S. America, China, Russia, India, The Middle East,
Asia, Australia, and Africa. To date, only a few sites have been treated using n-ZVM.
1.4.1
remediation costs
A typical PCE/TCE/DCE groundwater remediation costs around $200-$700 kg n-Fe
0
used [137, 162], and utilizes less than
1-280
t
n-Fe
0
for each t PCE/TCE/DCE in the soil/aquifer [17, 137]. The cost comprises a n-Fe
0
cost (e.g., $30-$100 kg
−1
) + injec-
tion/infiltration + monitoring costs. Since the radius of influence of an injection well/infiltration point source is typically less
than 40 m [22, 23], reducing the n-Fe
0
cost will not necessarily reduce the costs associated with injection/infiltration and mon-
itoring. Remediation adds value by either allowing the land to be rehabilitated, for industrial, domestic, or agricultural applica-
tions, or by allowing the water to be used for municipal, industrial or agricultural purposes. The sustainable remediation cost is
a function of the overall value added by the remediation.
1.4.1.1 Reduction of Type A Remediation Costs
Type A remediation costs are reduced by (i) reducing both particle size and
the amount of ZVM injected (Eq. 1.3). Compare with Figures 1.1b, c, which both achieved greater than 99% removal of
25-88 mg TCE l
−1
H
2
O [17]; (ii) increasing groundwater temperature [130] (Eq. 1.4, and/or oxygen levels [138, 2, 139-141],
and/or increasing groundwater acidity [10, 103, 104, 135, 142] (Eqs. 1.4 and 1.9), in order to both accelerate the remediation
and reduce the overall amount of n-Fe
0
required. The catalytic model assumes that 1 mol n-Fe
0
can only generate 2 or 3 mol
e
−
(Appendix 1.C) and that increasing particle size will increase the active life of the n-Fe
0
[163]. The galvanic model assumes
that the perpetual oscillations [10] within the groundwater will allow a substantially greater amount of e
−
and H
+
to be formed
using a cyclic process. That is,
1. H
2
O
−
+ Fe
2+
= FeH
2+
+ OH
−
; H + Fe
2+
= FeH
2+
;
2. H
3
O
+
+ FeH
2+
= H
2
O + H
2
+ Fe
3+
; H
2
= 2H
+
+ 2e
−
; H
+
+ e
−
= H
3. H + Fe
3+
= H
+
+ Fe
2+
[132]
Fresh oxygen contained in recharge water entering the remediation zone will be initially removed [132] as O
2
+ Fe
2+
= O
2
−
+ Fe
3+
;
O
2
+ FeOH
+
= O
2
−
+ FeOH
2+
; O
2
+ Fe(OH)
2
= O
2
−
+ Fe(OH)
2
+
, O
2
+ Fe(OH)
3
−
= O
2
−
+ Fe(OH)
3
, etc. The O
2
−
interacts with FeO
x
H
y
n
+/−
,
H
2
O, O
2
H, OH and H to form O
−
, O
2−
, O
2
O
2
H, OH, H
2
O
2
and FeO
x
H
y
n
+/−
[132]. This allows recharge of oxygenated water (from
surface precipitation and subsurface flow) to provide a natural drive for the galvanic cell.
1.4.1.1.1 Reduction of Type A Remediation Costs: Catalytic Model
The cathodic model focuses on reducing particle size
and increasing temperature to increase remediation rates and reduce the amount of ZVM required. Figures 1.1b, c demonstrate
that the same degree of TCE remediation can be achieved using 3.9 kg n-Fe
0
(>1000 nm) m
3
soil and 0.009 kg n-Fe
0
(50-300 nm)
m
3
soil. The total n-Fe
0
surface area in Figure 1.1b is about 20 times greater than the n-Fe
0
surface area in Figure 1.1c. Brownfield
development land may economically sustain a remediation cost of $3-$6 MM/acre (i.e., $75-$1500 m
3
soil/aquifer), depending
on location and final use. Comparative costs for surface reactor treatment of industrial water and agricultural water to remove
chlorinated hydrocarbons and nitrates using ZVM in fixed/packed bed reactors are in the order of $0.03 m
−3
H
2
O for greater than
90% removal [10, 13].
1.4.1.1.2 Reduction of Type A Remediation Costs: Galvanic Model
The galvanic model indicates that the concentration
of Fe
2+
, FeO
x
H
y
n
+/−
ions and the presence of a controlled instability in the groundwater following ZVM injection (e.g.,
temperature variation, oxygen variation, acidification) controls the rate of Type A remediation. These factors facilitate
remediation through electron shuttle reactions [164-166]. A galvanic cell of this type (Fig. 1.2) can be sustained through
greater than 200,000 cycles/oscillations [151]. Application of this model to brownfield site remediation will (i) reduce the
amount of n-Fe
0
required to achieve a specific level of remediation within a specific timeframe; and (ii) reduce the
remediation time required using a specific amount of n-Fe
0
. Remediation time frames for TCE removal can be potentially
reduced from >1 year to <1 week.
