INGENIEUR
INGENIEUR
Figure 3: Microbial fuel cell with two chambers; anode and cathode( PEM: proton exchange membrane).
modification is not of interest, mixing these wild types of microbes together during fermentation is seen as an alternative method, which is termed Simultaneous Saccharification and co- Fermentation( SSCF). It doesn’ t require sugar separation, and both glucose and xylose can be converted to ethanol. However, the drawbacks of mixed cultures include the difficulty in maintaining an optimum balance between both cultures, and the preparation of many inoculums before fermentation, which are a hassle for industrial applications. To overcome the limitations of using mixed cultures, genetic modification of a single microbe is desired to improve the feasibility of CBP method and improve the ethanol yield. This has been practiced by over expressing the genes from S. stipitis encoding xylose reductase( XR) and xylitol dehydrogenase( XDH) to enable xylose transportation into S. cerevisiae. Ethanol production was enhanced by over expressing the endogenous XK gene encoding xylulokinase. Another way is to carry out gene modification of natural ethanol producers to equip them with cellulotic properties. For example, yeast such as S. cerevisiae, P. stipitis, and various bacteria, namely Klebsiella oxytosa, Z. mobilis undergoing modification to include genes from cellulase producers( Trichoderma reesei, Aspergillus niger) to enable cellulase production.
From Lignocellulosic Biomass to Electricity
We can expand the potential utilisation of lignocellulosic biomass by transforming it into a more direct energy form, i. e. electricity. Green electricity, or some might term as renewable or sustainable electricity, has been extensively looked for all over the world. Green electricity is notably associated with electricity generator systems, for instance solar, wind and waterturbine energy systems that are now progressively being employed in commercialised projects by both developed and developing countries. Lignocellulosic based electricity in this instance, could also be one of those very promising near future green energy systems by incorporating it into a system called the bio-electrochemical system( BES).
One of the systematic tools in the BES principle is termed the microbial fuel cell( MFC). MFC is an emerging technology that generates electricity( bioelectricity) from biomass using bacteria. The liquid form of lignocellulosic or cellulosic biomass is oxidised by bacteria( anaerobes and / or aerobes) and the electrons released from the oxidation process are transferred to the electrode in an anode chamber and subsequently flows to a cathode chamber generating electricity( Figure 3).
60 VOL 75 JULY-SEPTEMBER 2018