Microbial Fuel Cells for Wastewater Treatment - Biotechnologies and Biomimetics for Civil Engineering - page 409

(Min et al. 2005 ) and U-shaped MFCs (Milliken and May 2007 ) (Fig. 18.2 a, b). In
the H-configuration, the membrane is clamped in the middle of the tubes connecting
the bottle. Although H-shape systems are usually available for basic parameter
research, they generate low power densities. This may attribute to high internal
resistance and electrode-based losses. Oh and colleagues demonstrated that the
power densities had a close relationship with the relative sizes (cross sections) of the
cathode to that of the anode and the membrane (Oh et al. 2004 ; Oh and Logan 2006 ).
Ringeisen and colleagues provided a miniature configuration of MFC (Mini-
MFC) with a total volume of 1.2 cm 3 (Fig. 18.2 c) (Ringeisen et al. 2006 ). As the
result of its specific structure, the mini-MFC maintains a large surface area to
volume ratio when graphite felt electrodes were used, enabling high power den-
sities to be attained. Min and Logan ( 2004 ) designed a Flat Plate MFC (FPMFC) to
treat domestic wastewater. The FPMFC was comprised of a single channel formed
between two nonconductive (polycarbonate) plates that were separated into two
halves by the electrode/PEM assembly (Fig. 18.2 d). The anode electrode was a
plain porous carbon paper (10 9 10 cm 2 ), while a carbon cloth combining a
platinum catalyst (0.5 mg/cm 2 catalyst containing 10 % Pt) servers as cathode
electrode. The wastewater was fed into the anode chamber and dry air could pass
through the cathode chamber without any catholyte, both in a continuous flow
mode. Average power density was obtained at 72 mW/m 2 (Min and Logan 2004 ).
Another reactor design, named upflow MFC (UMFC) working in continuous
flow mode, was first tested by He et al. ( 2005 ) (Fig. 18.2 e). Its configuration was
improved by combining the advantages of upflow anaerobic sludge blanket sys-
tem, which were operated in continuous mode. Another UMFC with a U-shaped
cathode installed inside the anode chamber was developed based on the above
configuration (He et al. 2006 ) (Fig. 18.2 f). A U-shaped cathode compartment with
a 2 cm diameter was constructed by gluing two tubes made from PEM into a
plastic base connector. In addition to a practical configuration, UMFC achieved
promising power outputs with a maximum volumetric power density of 29.2 W/m 3
with an overall internal resistance of 17.3 X (He et al. 2006 ). They suggested that
the main limitation to power generation was the internal resistance. Overall, these
systems seem to be more available for practical implementation as they are rel-
atively easy to scale up.
18.3.2 Single-Chamber MFC Systems
In the single-chamber MFC (SCMFC), the cathode is exposed directly to the air by
eliminating the cathodic compartment containing air-sparged solution (Park and
Zeikus 2003 ; Liu and Logan 2004 ; Liu et al. 2004 ) (Fig. 18.1 b). They typically
possess only an anode chamber without the requirement of aeration in the cathode
chamber. In comparison with dual chamber system, a SCMFC provides the sim-
plified design, increased mass transfer to the cathode, cost savings and an overall
decrease in reactor volume.