Extremophilic Microbes in Biohydrogen Production
Anniina T. Kivistö,
Ville P. Santala,
Matti T. Karp.
Hydrogen is considered a promising alternative for replacing fossil fuels in the future because of its high
energy content and non-polluting properties. Currently, biological production processes such as dark fermentation suffer
from contamination and efficiency issues. Extremophilic anaerobes that produce hydrogen via anaerobic fermentation are
promising organisms for the conversion of biomass and organic wastes to hydrogen in open (non-sterile) systems in which
the extreme process conditions efficiently prevent the growth of H2-consuming microorganisms. Furthermore,
extremophilic microorganisms are viable candidates for processing harsh (hot, highly saline, acidic or alkaline) organic
waste streams to valuable products. Recent studies have mainly focused on thermophiles due to the high H2 production
yields achieved at high temperature, while investigation on H2 production by other extremophilic organisms is still scarce.
This review discusses various groups of anaerobic extremophiles, including thermophiles, halophiles, acidophiles and
alkaliphiles, as hydrogen producers with emphasis on advantages, current challenges, production efficiencies, economical
substrates and process design.
Keywords: Acidophile, alkaliphile, alkalithermophile, bioenergy, biofuel, dark fermentation, extremophile, haloalkaliphile,
halophile, hydrogen, hydrogenase, light-independent, organic waste, plant biomass, renewable energy, thermophile.
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