Environmental Engineering Reference
In-Depth Information
Mesophilic
Hyper-thermophilic
Thermophilic
Cellulose
Seed sludge
Continuous Dark Fermentation
Hydrogen yield
Stability
Cellulose degradation
Microbiology
Fig. 8.5
Development of direct bioconversion of cellulose to hydrogen by continuous dark
fermentation using anaerobic mixed microflora. (Gadow et al.
2012
)
yield reaches the theoretical maximum of 4 mol H
2
/mole glucose, whereas at
mesophilic and thermophilic conditions, the hydrogen yield is typically less than
2 mol hydrogen per mole glucose.
2.
Pathogens are reduced
. High temperature minimizes contamination by hydro-
gen consumers such as methanogenic archaea, since the hydrogen-producing
reaction is favoured at high temperatures, and hydrogen utilization processes are
negatively affected with temperature increase.
Studies on the microbial hydrogen production structure of mixed cultures have been
carried out in the mesophilic and thermophilic temperature ranges. While a few
studies have been focused on hyper-thermophilic ranges using pure cultures, none
have involved the use of mixed microflora according to the approach in Fig.
8.5
,
which we now describe in more detail.
8.3.4
Temperature and Stability of Bio-Hydrogen Production
In the research approach in Fig.
8.5
, continuous H
2
fermentation was carried out
using three different temperatures (37, 55 and 80 ºC) in order to identify the best
conditions for H
2
production from cellulose, using the detailed configuration in
Fig.
8.6
. While a stable but low hydrogen production was obtained under mesophilic
temperatures, hydrogen production was higher and more stable under thermophilic
and hyper-thermophilic temperature conditions.
This experiment showed that the degradation efficiencies of cellulose and
hydrogen yield were increased as the temperature increased from mesophilic
through thermophilic to hyper-thermophilic temperatures. At 55 and 80 ºC, tem-
perature enhanced the ability of mixed culture to degrade cellulose to hydrogen,
consistent with other studies. At 37 ºC on the other hand, hydrogen and methane
were produced. The different reaction pathways at the three temperature ranges are
shown in Fig.
8.7
.
