Environmental Engineering Reference
In-Depth Information
2013
). By employing the
Desulfovibrio desulfur-
icans
which is a sulphate-reducing bacteria dem-
onstrated electricity generation along with 99 %
of sulphate removal (Zhao et al.
2008
). Sharma
et al. (
2013
) investigated various materials such
as activated carbon fabric and stainless steel for
cathodic SRB biofilm formation, and it was re-
ported that stainless steel as the more suitable
material for sulphate reduction.
pneumoniae
in the anodic compartment and bio-
mineralized manganese oxides were deposited
through electrochemical reduction reaction in the
cathode compartment by
Leptothrix discophora
.
The cathodic reduction reaction occurs directly
by accepting electrons on graphite electrode sur-
face. These depositions of manganese oxide do
not need any mediators. It was also demonstrated
that biomineralized manganese oxides are supe-
rior to oxygen by two times. To further explore
the viability of such a biocathode, Shantaram
et al. (
2005
) also used manganese anode sedi-
ment MFC, which is different from conventional
MFCs. Here, the oxidation of manganese helps
to drive the electrons from magnesium oxidation.
On complete oxidation, the anode needs to be re-
placed. Due to the high redox potential of man-
ganese oxide, this BES produced a maximum
voltage of 2.1 V. The voltage was further ampli-
fied to 3.3 V, which was sufficient to power a
wireless sensor. The study demonstrated, for the
first time, the application of BES to power small
electronic sensors and manganese compounds as
promising biocathodes for sediment BES. Iron,
which is also an abundant element also showed
its function in biocathode reduction. Although
iron compounds have been used as electron me-
diators in abiotic cathodes, previous studies have
revealed that Fe(II) is oxidized to Fe(III) through
microbial activity by
Thiobacillus ferrooxidans
(Nemati et al.
1998
). Researchers have adopted
this process to oxidize organics in an electrolytic
cell in which electrical energy is converted into
chemical energy, requiring an external voltage
supply (Lopez-Lopez et al.
1999
). In the cath-
ode chamber of this reactor,
T. ferrooxidans
was
grown to regenerate the ferric irons by obtaining
energy from the reaction and methanol was oxi-
dized in anode. A study by Lefebvre et al. (
2013
)
used metal scraps as cathodes and it was found
that metal scraps can be recycled in BES for en-
ergy generation. Even though this study was not
focused on any remediation, but it is providing
future possibilities microbial electroremediation
of metals oxides.
10.5.2
Metal Oxidation/Reduction
Metal oxide-reducing bacteria have been discov-
ered over the last 30 years. The microbes, ca-
pable for metal oxide reduction, were called as
dissimilatory metal-reducing bacteria (DMRB).
These bacteria have more interest due to their
applications in geobiological phenomena, biore-
mediation and biotechnology. Organisms such as
Clostridium
(Park et al.
2001
),
Geobacter
(Bond
and Lovley
2003
; Holmes et al.
2006
),
Aeromo-
nas
(Pham et al.
2003
),
Rhodoferax
(Chaudhuri
and Lovley
2003
),
Desulfobulbus
(Holmes et al.
2004
), and
Shewanella
(Chang et al.
2006
) in-
cluded in DMRB group. All of these DMRB have
also been shown to produce current in MFC sys-
tems (Bond and Lovley
2003
; Logan et al.
2006
)
as well as provens as good biocatalysts to produce
higher current densities.
Shewanella oneidensis
MR-1 is a Gram-negative facultative anaerobe
capable of utilizing a broad range of electron ac-
ceptors for bioelectricity generation.
S. oneiden-
sis
MR-1 can reduce Mn(IV) and Fe(III) oxides
and can produce current in MFCs. Deletion mu-
tants of this bacteria were generated and tested
for current production and metal oxide reduction
was evidenced that cytochromes play a key role in
bioelectricity generation (Bretschger et al.
2007
).
Metal oxidation is also possible in biocathode
configured BESs. Microorganisms present on
biocathode assist the oxidation of transition metal
compounds, such as Mn(II) or Fe(II), for electron
delivery to oxygen. In addition, bacteria in the
cathode benefited the reaction by supplying oxy-
gen. Rhoads et al. (
2005
) have operated a MFC
in which glucose was oxidized by
Klebsiella
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