Abstract
Diversification of biofuel sources has become an important energy issue. Bio-hydrogen production from microalgae has received much attention recently. However, commercial production of microalgae biofuels including bio-hydrogen is still not feasible due to the low biomass concentration and costly downstream processes. It has been reported that exposing some species of algae to environmental stress, e.g., by depriving the algae of sulfur in light, it is possible to produce significant amounts of hydrogen gas. However, this technology is still in its infancy and there is significant potential for technology development and improvement at every level. This review discusses the biological hydrogen production by microalgae (direct bio-photolysis, indirect bio-photolysis, photo fermentation and dark fermentation) and optimization of key parameters to enhance hydrogen production. The effects of different stress reactions on production of the valuable components are described. This knowledge can be used to evaluate the possibilities for producing hydrogen and high value products efficiently in the same process. Further studies of these topics may result in a sustainable process where solar energy can be converted into hydrogen in an integrated manner, where production efficiencies are sufficient for an economic exploitation of algal technology using algal stress reactions.
Highlights
Our current energy consumption worldwide is in the proximity of 15 TW, while the energy consumption rate in 2050 has been estimated to be at least 27 TW (Lewis and Nocera, 2006). The majority of this energy is at the moment obtained from fossil fuels and any change requires improved technology for use of alternative energy sources
The use of fossil fuels cause excessive global climate change because emissions of greenhouse pollutants and the formation of compounds COx, Nitrous Oxide (NOx), SOx, CxHy, ash and other organic compounds that are released into the atmosphere as a result of combustion
Global warming is caused by the emission of greenhouse gases. 72% of the totally emitted greenhouse gases are Carbon Dioxide (CO2), 18% Methane (CH4) and 9% Nitrous Oxide (NOx)
Summary
Our current energy consumption worldwide is in the proximity of 15 TW, while the energy consumption rate in 2050 has been estimated to be at least 27 TW (Lewis and Nocera, 2006). Among various hydrogen production facultative aerobic bacteria, cyanobacteria and lower processes, microbial/algal (biological) methods are eukaryotes (i.e., green algae and protists) produce H2 known to be less energy intensive, for it can be carried
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