Biomedical Engineering Reference
In-Depth Information
4
Challenges and Future Opportunities ...............................................................................
186
4.1
Challenges To Large-Scale Application ..................................................................
186
4.2
Future Directions ......................................................................................................
190
5
Conclusions........................................................................................................................
191
References ...............................................................................................................................
192
1 Introduction
Microbial fuel cells (MFCs) have emerged as a promising technology to meet the
dual goals of wastewater treatment and energy production in a sustainable way.
The idea of recovering electric energy from wastes through microbial metabolism
in MFCs has aroused tremendous interest and stimulated intensive research among
researchers and engineers all over the world. China in particular, as a country
constrained by both severe water pollution and energy crisis, has put great efforts
into the development of MFC technologies. In the past few years, China has
achieved significant progress in this field, as is shown by the dramatically
increased number of publications (Fig. 1 ). A comparison of the research activities
between China and the world clearly show that China is playing an increasingly
important role in this field. However, despite intensive studies and much progress,
there are significant challenges remaining.
The MFC in its basic form is a device that uses bacteria to catalyze electro-
chemical reactions and generate current. It typically consists of a bacteria-enriched
anode, a cathode and a separator between them [ 1 ]. A two-chamber or single-
chamber design can be adopted, each with specific advantages. A schematic
diagram of a typical two-chamber MFC is given in Fig. 2 . In such a two-chamber
setup, microorganisms oxidize organics in the anode chamber, producing protons
and electrons; electrons transfer through an external circuit (with resistor) to the
cathode and react with a final electron acceptor (mainly oxygen); the generated
protons continuously diffuse via the separator to the cathode chamber to sustain the
charge balance. However, researchers found that such two-chamber configurations
generally suffer from high aeration cost and are difficult to scale up due to high
overpotential. This has lead to the development of single-chamber MFCs [ 2 ].
In a single-chamber configuration, the cathode is exposed directly to the open air,
which enables more efficient oxygen utilization, no need for aeration, and a
compact reactor configuration. Moreover, membrane-less setups have been fre-
quently adopted in single-chamber systems to facilitate proton transfer. However,
this also increases the possibility of substrate loss and cathode biofouling. In recent
years, MFC configurations have further evolved from simple column or cube
reactors toward more bioreactor-type tubular systems [ 3 ] and integrated systems
[ 4 , 5 ], attributable to the rapid development of electrode and separator materials
[ 6 ] and the introduction of the biocathode concept. In a biocathode MFC, cost-
effective microorganisms instead of noble metals are used as the catalyst for
versatile cathode reduction reactions. Such a strategy has significantly expanded
the application scope of MFC technologies [ 7 ].
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