Environmental Engineering Reference
In-Depth Information
Table 2.3 Comparison of stoichiometrical and economical parameters of partial biodesaturation
of saturated soil with 50 % porosity
Electron
donor
Use of
electron
donor
(kg/m 3
Use of electron
acceptor
(sodium
nitrate) (kg/m 3
of N 2 )
Cost of
electron
donor ($/
kg)
Cost of
electron
acceptor
($/kg)
Estimated cost of
electron donor and
acceptor for 10 %
desaturation of soil ($/
m 3
of
N 2 )
of N 2 )
Ethanol
$0.60-0.70
$0.4-0.5
$0.25-$0.31
3.4
7.6
Acetic
acid
$0.60-0.70
$0.4-0.5
$0.25-$0.31
3.4
7.6
Glucose
$0.60-0.80
$0.4-0.5
$0.25-$0.31
3.4
7.6
The stoichiometrical parameters of these reactions are almost same: con-
sumption of electron donor is 3.4 kg/m 3 of N 2 and consumption of electron
acceptor (sodium nitrate) is 7.6 kg/m 3 of N 2 . The consumption of electron donor
and acceptor for 10 % (volume of gas/volume of water) desaturation of soil with
porosity 50 % is 0.55 kg/m 3 of saturated soil. Production of carbon dioxide in
reactions 2.1 - 2.3 , which is from 120 to 159 g/m 3 of N 2 or from 12 to 16 g/m 3 of
water in saturated soil with 50 % porosity, is not accounted for desaturation of soil
because solubility of CO 2 in water at 10 C is 2500 g/m 3 .
There is almost no cost difference between these electron donors: the cost of
electron donor is from $0.5 to $0.7/kg, the cost of electron acceptor (sodium
nitrate) is from $0.4 to $0.5/kg, so the estimated cost of electron donor and
acceptor for partial desaturation is from $5.1 to $6.2/m 3 of N 2 . The estimated cost
of electron donor and acceptor for 10 % (volume of gas/volume of water) desat-
uration of soil with porosity 50 % is from $0.25 to $0.31/m 3 of saturated soil.
However, even stoichiometrical and economic parameters of the electron donors
are similar, ethanol could be more preferable electron donor then acetic acid or
glucose sirup for geotechnical applications because it is liquid with neutral pH and
not corrosive substance with low viscosity.
Biocementation of loose sand using a MICP process to increase the liquefaction
resistance of sand has also been reported by DeJong et al. ( 2006 ), Montoya et al.
( 2012 ). It was shown (Montoya et al. 2012 ) that the resistance of sand to lique-
faction, as measured by a decrease in the excess pore water pressure ratio, was
significantly increased after MICP. However, sufficiently strong biocementation of
saturated sand, at the level of unconfined compressive strength 250-500 kPa,
could be at the content of precipitated calcium carbonate of 75-100 g/kg of sand
(Ivanov et al. 2012a; Cheng et al. 2013 ). Therefore, it could be material-con-
suming process requiring about 88 kg CaCl 2 and 96 kg of urea per 1 m 3 of sand,
which will cost at least $41/m 3 of saturated soil. This value is about 140 times
higher than 10 % desaturation of soil using biogas production in situ. So, bioce-
mentation of soil to mitigate liquefaction could be too expensive to be applicable
for large-scale geotechnical practice.
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