Ingenieur Vol. 75 ingenieur July 2018-FA | Page 63

Figure 4: Third/fourth generation microalgae-microbial fuel cell technology (Adapted from https://doi.
org/10.1016/j.biortech.2015.09.061).
The first observation of electrical current
generated by bacteria is generally credited to M.C.
Potter in 1911 and later, a few practical advances
in electro-physiological processes were achieved
(Lewis, 1966) which led to increasing interest in
fuel cells by the 1990s. In the recent decades,
great attention has been paid to MFC due to its
mild operating conditions and use of a variety of
biodegradable substrates, including lignocellulosic
biomass, as a feedstock. The customary MFC
consists of anode and cathode compartments
but there are single chamber MFCs that offer
more encouraging designs and electrical outputs.
By exploiting the active micro-organisms that
catabolise the substrate, the MFC could also be
utilised as a power generator in small devices
such as biosensors.
Numerous attempts of biomass substrate
utilisation in MFC systems that resulted in positive
electrical output have been recorded. Ranging
from agricultural by-products including corn
stover, farm manure, malt and yeast extracts, and
starch, to wastewaters from domestic, brewery,
industrial and food processing sources have been
used. It has been discovered that the presence of
fermentable substrates, for example, glucose and
acetate, that are easily derived from pre-treated
substrate biomass, could improve the power
generation of the MFC system. The use of glucose
has been found to stabilise the anode potential
through microbial activities, suggesting that this
substrate has a positive influence on current
generation. Not long after this generation was
actively used in real applications, the third and
most recent fourth generation biofuels evolved
involving algae and/or microalgae biomass. The
third generation is basically processing of algae
biomass while the fourth is about metabolic
engineering of algae in producing biofuels from
oxygenic photosynthetic micro-organisms. The
advancement of the third and fourth generations
in biofuel production have had an impact on MFC
processing as well.
Let’s first have a look at this current R&D trend
in integrating microalgae-photobioreactors into
the MFC system or in short, MP-MFC (Figure 4).
Although the challenges and prospects of this
integrated system have been outlined, the diverse
conditions in which algae can easily grow make
this system worthy of serious consideration.
The photosynthetic reaction by the microalgae
(Chlorella vulgaris) in the cathode chamber
produces oxygen that functions as an electron
acceptor. The residue or biomass from microalgae
61