Environmental Engineering Reference
In-Depth Information
Fig. 8.21
Operation performance of hydrogen and methane production from food waste in a two-
stage process. (Chu et al.
2010
)
simultaneously from waste potentially feasible on both economic and technical
grounds. Figure
8.21
shows the operation performance for hydrogen and methane
production from food waste from an average of two runs (Run1: 55 ºC H
2
reactor
35 ºC CH
4
reactor; Run2: 55.8 ºC H
2
reactor 55 ºC CH
4
reactor). In the hydrogen
production stage, biogas production rate was stable at 10.4 l/l/d and composed of
H
2
(52-56 %) and CO
2
(41-47 %) with no CH
4
detected. In the mesophilic or ther-
mophilic methanogenic phases, biogas production rate was stable at 4.7 l/l/d and
composed of CH
4
(70-80 %) and CO
2
(20-29 %). H
2
and CH
4
production appeared
to be more dependent on the composition of waste than fermentative temperature;
moreover the methanogenic reactor was more effective in hydrolysis and removal
of food waste at thermophilic temperatures.
Three important advantages of this process can also be emphasized. First,
enriching H
2
-producing bacteria can be achieved by optimizing design parameters
such as pH, HRT and temperature, and using mixed-seed organisms without any
inoculum pre-treatment. Second, hydrogenesis in thermophilic condition can replace
the pre-treatment of feedstock to kill pathogens in waste materials and suppress the
indigenous microorganisms; moreover diversity of H
2
producing microflora can
be achieved. Third, this study represents the first finding of the
Clostridium
sp.
strain Z6, which was found to be the predominant H
2
-producing bacteria, in this
thermophilic H
2
fermentative system.
8.5
Conclusions
Experience of applying dark fermentation to the treatment of various types of or-
ganic wastes is long-established and has already made a significant contribution
to improving the recovery of resources and providing local sources of renewable
energy in the form of bio-methane in a single-phase process. However, recent re-
search suggests that the potential for bio-hydrogen production is also significant
and further research and development may lead to economically viable two-stage
