2.6.7 Hybrid System Using Photosynthetic and Fermentative
Bacteria:
Hybrid systems comprise of two systems as dark fermentation with photofermentation process which involves both non-photosynthetic and photosynthetic
bacteria. Dark fermentation produces hydrogen at high rates with simple reactor
design along with the by-products as volatile fatty acids. These volatile fatty acids
become substrate for the second stage in hybrid system as photofermentation which
convert them to hydrogen. This will ultimately increase the hydrogen concentration
and overall yield.
The combination of the two systems enables to have high hydrogen production
yield and also decreases the amount of the light energy required for photosynthetic
bacteria (Lam et al. 2019).
2.6.8 Microbial Electrolysis Cell
Microbial fuel cells convert organic substrate to electricity to exoelectrogens.
Exoelctrogens are microorganism which convert organic substrate to electrons not
hydrogen. Hydrogen can be produced by modifying microbial fuel cells to microbial
electrolysis cells by adding small voltage to the fuel cell produced by bacteria and
creating anaerobic conditions. Microbes will decompose organic substrate in the
anode chamber and this anode act as an electron acceptor. There are two stages: first
is dark fermentation in which microbes produces hydrogen and second is
electrohydrogenesis.
Microbial electrolysis cell uses a wide range of organics as substrates along with
microbes such as Geobacter, Pseudomonas and Shewanella spp. Microbial electrolysis cells generally give high hydrogen rate in terms of electron recovery (Singh and
Das 2019).
Biohydrogen produced by different methods have advantages over thermochemical methods as they can be produced at less atmospheric temperatures and less
energy-intensive, environment friendly but also utilized renewable energy resources
(Das and Veziroǧlu 2001; Merlin Christy et al. 2014; Rahman et al. 2015; Bardhan
et al. 2019; Lazaro and Hallenbeck 2019; Usman et al. 2019).
2.6.9 Biohydrogen Production from Algae
Algae are third-generation renewable feedstock for the production of hydrogen.
They are beneficial over other feedstock with the fact that it requires no land to be
used and also they have high photosynthetic efficiencies. Algae are of two types:
microalgae and macroalgae. Macroalgae are seaweeds mainly observed in marine
2 Application of Microorganisms for Biofuel Production
55
Bacteria:
Hybrid systems comprise of two systems as dark fermentation with photofermentation process which involves both non-photosynthetic and photosynthetic
bacteria. Dark fermentation produces hydrogen at high rates with simple reactor
design along with the by-products as volatile fatty acids. These volatile fatty acids
become substrate for the second stage in hybrid system as photofermentation which
convert them to hydrogen. This will ultimately increase the hydrogen concentration
and overall yield.
The combination of the two systems enables to have high hydrogen production
yield and also decreases the amount of the light energy required for photosynthetic
bacteria (Lam et al. 2019).
2.6.8 Microbial Electrolysis Cell
Microbial fuel cells convert organic substrate to electricity to exoelectrogens.
Exoelctrogens are microorganism which convert organic substrate to electrons not
hydrogen. Hydrogen can be produced by modifying microbial fuel cells to microbial
electrolysis cells by adding small voltage to the fuel cell produced by bacteria and
creating anaerobic conditions. Microbes will decompose organic substrate in the
anode chamber and this anode act as an electron acceptor. There are two stages: first
is dark fermentation in which microbes produces hydrogen and second is
electrohydrogenesis.
Microbial electrolysis cell uses a wide range of organics as substrates along with
microbes such as Geobacter, Pseudomonas and Shewanella spp. Microbial electrolysis cells generally give high hydrogen rate in terms of electron recovery (Singh and
Das 2019).
Biohydrogen produced by different methods have advantages over thermochemical methods as they can be produced at less atmospheric temperatures and less
energy-intensive, environment friendly but also utilized renewable energy resources
(Das and Veziroǧlu 2001; Merlin Christy et al. 2014; Rahman et al. 2015; Bardhan
et al. 2019; Lazaro and Hallenbeck 2019; Usman et al. 2019).
2.6.9 Biohydrogen Production from Algae
Algae are third-generation renewable feedstock for the production of hydrogen.
They are beneficial over other feedstock with the fact that it requires no land to be
used and also they have high photosynthetic efficiencies. Algae are of two types:
microalgae and macroalgae. Macroalgae are seaweeds mainly observed in marine
2 Application of Microorganisms for Biofuel Production
55