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in H 2 production and six-fold increase in hydrogenase activity was observed by
increasing the FeSO 4 concentration from 2.7 to 10.9 mg/l [137]. The role of metal
ions (Mn + ,Mg +2 ,Fe +3 , etc.) as well as primary and secondary metabolites (adeno-
sine mono phosphate, phosphoenolpyruvate, etc.) which have stimulation effects on
the enzymatic activity pertaining to fermentative H 2 production need to be studied
to enumurate their specific function.
7.7 Molecular Engineering
Metabolic engineering is one of the promising areas which can be advanta-
geously used to enhance H 2 production rate in dark fermentation processes. By
the use of recombinant DNA technology one can try to restructure metabolic
network to improve the production of H 2 . Microbial metabolic manipulation by
gene over expression, mutation and gene knocking out techniques were used for
this purpose. H 2 molar yields can be increased significantly through metabolic engi-
neering efforts [109]. Table 6 documents some of the work carried out in this area
pertaining to fermentative H 2 production. By engineering the genetic expression of
microorganisms the H 2 production rate can be influenced directly or indirectly.
8 Microbial Fuel Cell (MFC) - Bioelectricity Generation
from Acidogenic Fermentation
Although H 2 produced from dark fermentation process is considered as a viable
alternative fuel and energy carrier of the future, H 2 storage, purification, low pro-
duction rates and the requirements of separate fuel cell systems for the generation of
energy (electricity) are some of the inherent limitations. Alternatively, the microbial
fuel cell (MFC) facilitates in situ conversion of energy in the form of bioelectricity
from wastewater treatment by dark fermentation [111, 147-158]. MFC is a hybrid
bio-electrochemical system, which converts the substrate directly into electricity by
the oxidation of organic matter in the presence of bacteria (bio-catalyst) at ambi-
ent temperature/pressure [155, 156]. The potential developed between the bacterial
metabolic activity [reduction reaction generating electrons (e - ) and protons (H + )]
and electron acceptor conditions separated by a membrane manifests bioelectricity
generation. In an acidogenic microenvironment, single and dual chambered MFC
systems were evaluated for the production of bioelectricity using various types
of wastewater viz., chemical wastewater, designed synthetic wastewater, domes-
tic sewage and vegetable waste employing mixed cultures as anodic biocatalysts
[147-158] (Table 7). The higher activity of intracellular e - carriers which will help
in the translocation of e - from bacteria to the outside of the cell might be the rea-
son for higher current generation observed under acidic pH operation [156]. Apart
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