Environmental Engineering Reference
In-Depth Information
Table 1.3 Comparison of coulombic efficiencies (CCE or RCE) obtained in various MFC
studies
Reference
Value (%)
Definition
Substrate
Comments
a,b
Rabaey et al. (2005) [44]
75
CCE
Acetate
b
59
Glucose
a,b
Freguia et al. (2007) [48]
70-100
CCE
Acetate
b
40-60
Glucose
a,b
Lee et al. (2007) [21]
71
CCE
Acetate
b
49
Glucose
a,b
Torres et al. (2007) [21]
86
RCE
Acetate
b
49
Ethanol
a,b
Rozendal et al. (2006) [49]
92
RCE
Acetate
a
Min and Logan (2004) [18]
65
RCE
Acetate
28-50 Butyrate
14 Glucose
a
Acetate was the non-fermentable substrate, leading to low byproduct formation and biomass
production.
b
An alternate electron acceptor was used for these studies (ferricyanide or water),
eliminating the diffusion of oxygen into the reactor (J
O2
0).
TE near 1 indicates an efficient removal of COD, which is a desirable
attribute for a wastewater treatment process. A small TE, close to zero, indi-
cates poor effluent quality, especially for MFCs with a high initial COD
in
, and it
may indicate a requirement for post treatment to improve the COD removal. A
poor TE can result from disproportionately high influent COD and the pre-
sence of refractory organic compounds.
FoSaC evaluates the degree to which the electrical current achieved the
stabilization of COD. The definition of the FoSaC is
FoSaC
¼
AJ
e
=
A
ð
J
e
þ
J
H
;
gas
þ
J
O2
Þ
(1
:
23)
Since a major goal of operating an MFC is to achieve stabilization through
generating electrical current, a high FoSaC value is generally desirable. In contrast,
stabilization through J
O2
is undesirable, because the energy value of waste is lost.
High stabilization as removal J
H,gas
has mixed benefits. Depending on the gas
quality, byproducts such as hydrogen and methane can be collected to generate
useful energy. However, if these gaseous byproducts are not used for energy
generation, the energy value of the CODremoved is lost.When gaseous byproducts
are H
2
SandCH
4
, these gases must be captured to prevent environment pollution.
Once the coulombic efficiency and voltage efficiency are known, the final
ECE can be calculated as the product of both efficiencies:
E
out
E
substance
ECE
¼
VE
CCE
¼
VE
FoSaC
TE
¼
(1
:
24)
CCE is simply a product of TE and FoSaC. ECE is the fraction of the total
energy contained in the original waste or substrate (E
substrate
) that was
