Page 255 - Lignocellulosic Biomass to Liquid Biofuels

Syngas fermentation to bioethanol 211

to maintain within the ranges of 37°C 40°C, whereas for thermophilic
bacteria it is 55°C 80°C [4].

6.6.4 Gas flow rate
The microbial growth rate and its metabolic activities are affected by the
substrates used in syngas fermentation. Consequently, the partial pressures
of syngas components should be carefully controlled and kept at optimum
values.

6.6.5 Mass transfer

The vital factor for syngas fermentation is limiting the mass-transfer rate
from gas to liquid. The efficiency of mass-transfer rate among different
fermenter can be compared by the evaluation of gas liquid volumetric
mass-transfer coefficient. This parameter also gives information about the
hydrodynamic condition of the bioreactor. Thus the design of the biore-
actor is very much significant for syngas fermentation.

6.6.6 Trace metals

The trace metal components contained in syngas and acted as an impurity.
It plays a significant role in enhancing the microbial growth during the
syngas fermentation. It has the ability to adopt an iron concentration of
10 times higher in comparison to the standard medium used for the
fermentation of C. carboxidivorans. As a result, the ethanol production is
doubled, and the production of acetic acid and butyric acid is reduced.

6.6.7 Reducing agent
The bioethanol production during syngas fermentation may affect the
level of oxygen concentration, which is required to be optimized. As a
result, the growth rate of the microorganisms can be maximized. In addi-
tion, higher levels of oxygen concentration can decrease the growth rate
of anaerobic bacteria.

6.7 Roles of nanoparticles on syngas fermentation

Nowadays, more attention has been taken for the enhancement of etha-
nol yield produced from the syngas fermentation. In this regard, different
types of nanoparticles are usually used for enhancing the production rate.
Zhu et al. [54] reported that the increase of H 2 yield is due to enhanced