Waste to Renewable Energy: A Sustainable and Green Approach Towards Production of Biohydrogen by Acidogenic Fermentation - Sustainable Biotechnology: Sources of Renewable Energy - page 152

Ta b l e 5 Details of some of elements which may stimulate fermentative H 2 production process

Substance Function Reference

Mg +2 Activates the -subunit of catalytic site of E1 of

pyruvate dehydrogenase complex (PDC)
Activates the cytochromes for the efficient
electron transfer

α [127, 128]

Ni +2 Important component for cell growth and [Ni-Fe]

hydrogenase activity

[91, 129]

Fe +3 Acts as micronutrient and mediates between

hydrogenase and nicotinamide adenine
dinucleotide (NADH)- ferredoxin reductase as
electron carrier

[54]

Mn +

Activates the Ni-hydrogenases and Ni-Fe
hydrogenases

[127, 128]

Nitrogen Helps in bacterial growth as nutrient and

important constituent of all enzymes

[104]

Phosphorous Has nutritious value and provides buffering

capacity

[91]

Phosphoenol
pyruvate

Activates the α -subunit of the catalytic site of E1 [127, 128]

of PDC

Adenosine
mono
phosphate

Activates the α -subunit of the catalytic site of E1 [127, 128]

of PDC

Activates the NADH-dehydrogenase for the H +
removal from the redox mediator (NAD + )
facilitaing H 2 formation

Acidic pH [127]

[Ni-Fe] hydrogenases have a higher substrate affinity [131]. During H 2 production
process catalyzed by the [Ni-Fe] hydrogenases, electrons are transported through
an intra-molecular electron transfer chain from the redox partner such as NADH or
NADPH to the active site, meanwhile, H + are also transferred to the active site, and
gets reduced by the e - to produce H 2 [132, 133]. Since nickel is a fundamental com-
ponent in [Ni-Fe] hydrogenases, it may influence the fermentative H 2 production by
influencing the activity of [Ni-Fe] hydrogenases and thus plays an important role
in fermentative H 2 production [91, 129]. A trace level of nickel is required for acti-
vation or function of [Ni-Fe] hydrogenases and thus is conducive to fermentative
H 2 production [134]. Enhanced H 2 production potential was observed with increas-
ing Ni 2+ concentration from 0 to 0.1 mg/l [91]. Trace metals such as magnesium,
sodium, zinc and iron showed considerable affect on the fermentative H 2 produc-
tion with magnesium being the most significant one [134]. A nutrient formulation
containing these four trace metals has shown a 66% enhanced H 2 production rate
as compared to the control. Iron is an important element which helps to mediate
between hydrogenase and nicotinamide adenine dinucleotide (NADH)-ferredoxin
reductase [135, 136]. Low iron concentration limits hydrogenase activity to effi-
ciently mediate a reversible reaction between H 2 and an electron donor such as
reduced ferredoxin, thereby limiting H 2 production [2]. About a 1.59-fold increase