Hydrogen has the highest energy content per unit mass when compared to fuel types. When used as fuel, the product released to the atmosphere is only water or water vapor. Hydrogen gas can be produced by solar energy, wind, wave and biomass. Although biohydrogen studies help determine the biomass types that can serve as an alternative to fossil fuels while having a lower environmental impact, the selected biohydrogen production methods should also be cost-effective and sustainable at an industrial scale. Since pretreatments and their supply and some high-cost microorganism species affect the cost of hydrogen production, they should be taken into account to determine the economic applicability of a given biomass. The paper reviews the current gaps in the related information by classifying the biomass (according to whether pretreatment was used or not) used in the biohydrogen production through dark fermentation and anaerobic decomposition contains the following: (i) synthetic wastewaters. (ii) non-synthetic wastes/wastewaters; (a) Biohydrogen production using non-pretreated wastes/wastewaters and mixed microorganisms, (b) Biohydrogen production using non-pretreated wastes/wastewaters and certain microorganism species, (c) Biohydrogen production using pretreated wastes/wastewaters and mixed microorganisms, (d) Biohydrogen production using pretreated wastes/wastewaters and certain microorganism species.
