Environmental Engineering Reference
In-Depth Information
+ →+
()
2
CH COOH HO light H Oc
+
4
8
4
3
2
2
2
Overall reaction
:12H O
+ →+
light
12H
6O
2
2
2
2.3 Photo-Fermentation
(
)
CH COOH
++→+
2H O
light
4H
2CO
purple bacteria, microalgae
3
2
2
2
2.4
Water-Gas Shift Reaction
(
)
CO
+ →+
2
HO
HCOfermentative bacteria photosynthetic bacteria
,
2
2
2.5
Two-Phase Anaerobic Process
(
)
CH OHO4H
+ →+
2
2
HCOOH
+
2
CO
fermentative bacteria
6 26
2
2
3
2
(
)
2
CH COOH
→+
2
CH
2
CO
methanogenic bacteria
3
4
2
2.6
Hybrid Hydrogen Production System (Dark Fermentation
+ Photo-Fermentation)
Biohydrogen production methods can also be grouped into light independent pro-
cesses (dark anaerobic fermentation) and light dependent hydrogen production
methods with or without oxygen evolution (bio-photolysis) in terms of the energy
sources and electron donors used by microorganisms. Light-dependent hydrogen
results from the process of photosynthesis. Among photosynthesizing microorgan-
isms capable of evolving hydrogen most attention is paid to microalgae, heterocyst
cyanobacteria, and purple non-sulfur bacteria. Microalgae and cyanobacteria pos-
sess two photo-systems and can decompose water to release oxygen. Bacteria with
one photosystem (first of all purple and green sulfur and non-sulfur bacteria) are
incapable of evolving oxygen, and need more reduced electron donors than water to
affect photosynthesis. Biohydrogen processes can convert high carbohydrate con-
tent waste streams into useable renewable energy, while reducing waste disposal
costs and negative environmental impacts. The main criteria for the selection of