Microbial Fuel Cells for Wastewater Treatment - Biotechnologies and Biomimetics for Civil Engineering - page 423

organics and diverse microorganisms such as methanogens. This may lead to an
inferiority of electroactive biofilm due to methanogenic competition or metabolic
diversity. The low ionic strength of real wastewater can limit the power output of
MFCs as well (Rozendal et al. 2008 ). In addition, there are physical constraints
with regard to linearly scaling up MFCs. Excessive pressure because of hydrostatic
head could require variable permeability to regulate water loss and cathode
hydration in the case of permeable membrane. Most importantly, the greatest
hindrance lies in the increasing electrical losses and overpotentials with enlarged
size (Oh et al. 2010 ). All of this means that innovative reactor designs are required
for practically useful MFCs. As a consequence, after more than two decades of
development, in which numerous studies have focused on MFC's application for
wastewater treatment (Habermann and Pommer 1991 ), successful full-scale

application is still relatively rare.
In view of the concept of MFCs with current wastewater treatment system,
several types of MFCs have been proposed. In order to enhance the quality of
effluent, Logan ( 2008 ) proposed an integrated bioprocess, which combined the
post-treatment process, e.g., solids contact (SC) process or membrane bioreactor
(MBR) with MFC system (Fig. 18.6 a and b). However, performance of post
bioreactor can be inhibited due to consumption of most organic matter in the
preceding MFC. The MFC can be combined into the existing wastewater treatment
facilities as well. Min and Angelidaki ( 2008 ) developed a submersible MFC by
immersing an air-cathode MFC in an anaerobic reactor. Similarly, Cha et al.
( 2010 ) submerged a single chamber MFC into the aeration tank of the activated
sludge process to optimize the cell configuration and electrode materials. The
submersible MFC can be applied to the anaerobic (or aerobic) facility as an anode
(or cathode) chamber without additional constructions (Min and Angelidaki 2008 ;
Cha et al. 2010 ) (Fig. 18.6 c, d). Yu et al. ( 2011 and Feng et al. ( 2013b ) designed
another configuration for decentralized wastewater treatment through immersing
the anode into an anaerobic tank and the cathode into an aerobic tank of the A/O
system, respectively (Fig. 18.6 e). These types of configuration enable MFCs to be
applied to existing wastewater treatment systems.
Meanwhile, the work on scaling up MFCs for wastewater treatment is moving
forward. According to some information on the Internet or public literatures, there
are at least two pilot-scale MFCs for wastewater treatment available for practical
implementation. The first large-scale test of tubular MFCs was located at Foster's
brewery in Yatala, Queensland (Australia) ( http://www.microbialfuelcell.org ).
This system was constructed by the Advanced Water Management Center of the
University of Queensland, led by Jurg Keller and Korneel Rabaey. MFCs consisted
of 12 modules with an entire volume of 1 m 3 . The anodes and cathodes are made
of carbon fiber based on a brush design. Another pilot-scale multi-anode/cathode
MFC (MAC MFC) was developed by researchers of University of Connecticut and
their collaborators (Fuss and O'Neill, and Hydroqual Inc.) in the USA (Jiang et al.
2011 ). The MAC MFC contained 12 anodes/cathodes with a total volume of 20 L.
The reactors contain graphite rods as the anode, with Cu-MnO 2 or Co-MnO 2
catalyzed carbon cloth cathodes. The systems are treating wastewater, achieving