Environmental Engineering Reference
In-Depth Information
Fig. 10.3 Schematic
diagram of microbial
desalination cell (  AEM
anion exchange membrane,
CEM cation exchange
membrane)
oxygen, while cations (such as Na + ) in the middle
chamber transfer across the CEM to the cathode.
This proceeds to water desalination in the middle
chamber, without consuming additional external
energy. On top of it, electricity can be produced
from the treatment of wastewater by exoelectro-
genic bacteria in anode (Cao et al. 2009 ; Chen
et al. 2011 ). The electrode reactions create an
electric potential gradient up to about 1.1 V (open
circuit condition with acetate as organic source
at pH = 7 and partial pressure of oxygen in air is
0.2 atm) (Kim and Logan 2013 ). This potential
drives the process of desalination as explained
above.
On compilation of various studies for the
minimum and maximum salinity removal by
MDCs, it was found between 11 % and 100 %,
respectively, using 30 g/L salt water (Jacobson
et al. 2011 ). Salinity removals can be above 90 %
when the salt water concentration is increased to
35 g/L NaCl solutions which have similar con-
ductivities like marine water (Cao et al. 2009 ;
Kim and Logan 2011 ). However, very high sa-
linity removals require large volume of nonsalty
water in both anolyte and catholyte with 55-133
times the volumes of desalinated water (Kim and
Logan 2013 ). The use of stacked MDCs can re-
duce the need for large amounts of nonsalty elec-
wastewater is used as the source of the organic
matter that required for development of potential
gradient, the MDC can achieve three goals such
as desalination, energy production and wastewa-
ter treatment (Kim and Logan 2013 ). Basic de-
sign of MDCs consists of three chambers sepa-
rated by two membranes (Fig. 10.3 , Table 10.3 ).
As the desalination chamber is fixed in middle,
both anode and cathode chambers were attached
to the both sides of the desalination chamber.
Anode and desalination chambers separated by
anion exchange membrane (AEM) whereas,
cathode and desalination chambers separated by
cation exchange membrane (CEM). In another
way, it can be viewed as inserting an AEM next
to the anode and a CEM next to the cathode of
a MFC, with the salt solution to be desalinated
filled in the middle desalination chamber. The
electricity-generating mechanism of MDC is
similar to that of MFC. Current is generated by
the bacteria on the anode from oxidization or-
ganics, and electrons and protons are released to
the anode and anolyte, respectively (Logan et al.
2006 ; Chen et al. 2011 ). As cations are prevented
from leaving the anode chamber by the AEM,
anions (such as Cl ) move from the middle de-
salination chamber to the anode. In the cathode,
protons are consumed in the reduction reaction of
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