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