Another strategy to improve H 2 productivity of dark fermentation is the addition
of metals. These are required as enzyme co-factors improving their activity and
consequently leading to an increase of H 2 production. The improvement of
microbial growth and enzyme activity by supplementation of certain metals like Cu,
Fe and Ni has been documented in several studies [69, 71]. Moreover, the incorporation of metal nanoparticles (NPs) to improve dark fermentation has been
investigated in the last years [69, 70, 89, 90]. It was demonstrated that the presence
of nanoparticles of silver, iron, titanium oxide and nickel enhance the efficiency,
yield and rate of hydrogen production [69, 70, 89]. The incorporation of FeO NPs
in a dark fermentation process was shown to increase the hydrogen production yield
up to 17% [91]. This improvement was explained by the zero valency of the NPs
that can react with oxygen promoting the decrease of dissolved oxygen levels in the
media, which may increase the efficiency of the oxygen sensitive hydrogenases.
A highly significant enhancement of hydrogen yield from dark fermentation of
dairy wastewater was also reported when Ni NPs were added [89]. Moreover, the
combination of Fe and Ni NPs allowed an increase of more than 200% in H 2
production from lignocellulosic wastes [92]. Significant improvements were
achieved for H 2 production from industrial wastewaters when a nickel-graphene
nanocomposite was also incorporated in the bioprocess (reaching an improvement
of more than 100%) [93]. TiO 2 NPs-enhanced BioH 2 production by pretreatment of
organic wastes. TiO 2 nanoparticles can degrade the polysaccharides and proteins
into smaller organic compounds that are further utilized by the H 2 -producing
microorganisms [94].
3.2 Biohydrogen Production from One-Carbon Substrates
Another attractive class of substrates for biohydrogen production are one-carbon
compounds like formate and carbon monoxide [95–97]. CO is a cheap compound
that is present in syngas and several industrial waste gases. Therefore, the production of BioH 2 from these CO-containing gases contributes also for waste
recycling and minimization of carbon emissions. On other hand, formate is an
efficient H 2 carrier [97, 98] and can be easily obtained by biomass processing or
hydrogenation of carbon dioxide [99–101].
Biological conversion of one-carbon substrates to H 2 is an environmentally
friendly and economical approach since high specificity and high yields can be
achieved with a minimum energy input [95, 97, 102].
3.2.1 Whole-Cell Biocatalysts for Formate-Driven H 2 Production
The first reports of H 2 bioproduction from formate were obtained with E. coli [103],
and since then several microorganisms belonging to distinct phylogenetic groups
have been reported as biocatalysts for formate conversion to H 2 [102]. The biological conversion of formate to H 2 proceeds according to the reaction:
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M. Martins et al.
of metals. These are required as enzyme co-factors improving their activity and
consequently leading to an increase of H 2 production. The improvement of
microbial growth and enzyme activity by supplementation of certain metals like Cu,
Fe and Ni has been documented in several studies [69, 71]. Moreover, the incorporation of metal nanoparticles (NPs) to improve dark fermentation has been
investigated in the last years [69, 70, 89, 90]. It was demonstrated that the presence
of nanoparticles of silver, iron, titanium oxide and nickel enhance the efficiency,
yield and rate of hydrogen production [69, 70, 89]. The incorporation of FeO NPs
in a dark fermentation process was shown to increase the hydrogen production yield
up to 17% [91]. This improvement was explained by the zero valency of the NPs
that can react with oxygen promoting the decrease of dissolved oxygen levels in the
media, which may increase the efficiency of the oxygen sensitive hydrogenases.
A highly significant enhancement of hydrogen yield from dark fermentation of
dairy wastewater was also reported when Ni NPs were added [89]. Moreover, the
combination of Fe and Ni NPs allowed an increase of more than 200% in H 2
production from lignocellulosic wastes [92]. Significant improvements were
achieved for H 2 production from industrial wastewaters when a nickel-graphene
nanocomposite was also incorporated in the bioprocess (reaching an improvement
of more than 100%) [93]. TiO 2 NPs-enhanced BioH 2 production by pretreatment of
organic wastes. TiO 2 nanoparticles can degrade the polysaccharides and proteins
into smaller organic compounds that are further utilized by the H 2 -producing
microorganisms [94].
3.2 Biohydrogen Production from One-Carbon Substrates
Another attractive class of substrates for biohydrogen production are one-carbon
compounds like formate and carbon monoxide [95–97]. CO is a cheap compound
that is present in syngas and several industrial waste gases. Therefore, the production of BioH 2 from these CO-containing gases contributes also for waste
recycling and minimization of carbon emissions. On other hand, formate is an
efficient H 2 carrier [97, 98] and can be easily obtained by biomass processing or
hydrogenation of carbon dioxide [99–101].
Biological conversion of one-carbon substrates to H 2 is an environmentally
friendly and economical approach since high specificity and high yields can be
achieved with a minimum energy input [95, 97, 102].
3.2.1 Whole-Cell Biocatalysts for Formate-Driven H 2 Production
The first reports of H 2 bioproduction from formate were obtained with E. coli [103],
and since then several microorganisms belonging to distinct phylogenetic groups
have been reported as biocatalysts for formate conversion to H 2 [102]. The biological conversion of formate to H 2 proceeds according to the reaction:
262
M. Martins et al.