Environmental Engineering Reference
In-Depth Information
TABLE 4.7 The Main Advantages of Different Biological Hydrogen
Production Processes
Process
Advantages
Direct biophotolysis
It can produce H 2 directly from water and sunlight.
Solar conversion energy increased by 10-fold as
compared with trees and crops
Indirect biophotolysis
It can produce H 2 from water. Has the ability to fix N 2
from atmosphere
Photofermentation
A wide spectral light energy can be used by these
bacteria.
It can use different waste materials, such as distillery
effluents, and waste
Dark fermentation
It can produce H 2 all day long without light. A variety of
carbon sources can be used as substrates.
It produces valuable metabolites such as butyric, lactic,
and acetic acids as by products. It is anaerobic
process, so there is no O 2 limitation problem.
Hybrid reactor system (combined
dark and photofermentation)
Two-stage fermentation can improve the overall yield of
hydrogen
Source : Reproduced with permission from Nath and Das [66].
composition), is termed ''biohydrogen.'' Biological hydrogen production
processes are found to be more environment friendly and less energy inten-
sive as compared with thermochemical and electrochemical processes [62].
Researchers have started to investigate hydrogen production with anaerobic
bacteria since 1980s [63-65]. The main advantages of different biological
hydrogen production processes are given in Table 4.7 [66].
The processes of biological hydrogen production can be broadly classified
into two distinct groups. One is light-dependent and the other is light-
independent process. Specific ways in which microorganisms can produce
H 2 include biophotolysis of water using green algae and blue-green algae
(cyanobacteria), photofermentation, dark fermentation, and hybrid reactor
system [67].
There are three types of microorganisms of biohydrogen generation: cya-
nobacteria, anaerobic bacteria, and fermentative bacteria. The cyanobacteria
directly decompose water to biohydrogen and oxygen in the presence of light
energy by photosynthesis. Photosynthetic bacteria use organic substrates like
organic acids. Anaerobic bacteria use organic substances as the sole source
of electrons and energy, converting them into biohydrogen. Biological hydro-
gen can be generated from plants by biophotolysis of water using microalgae
(green algae and cyanobacteria), fermentation of organic compounds,
and photodecomposition of organic compounds by photo-synthetic bacteria
[63]. All processes of biological hydrogen production are fundamentally
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