ABSTRACT
Hydrogen has emerged as a promising alternative to the petroleum-based fossil fuels because it is clean, renewable, has high energy density (per unit mass), and is carbon neutral. Biological hydrogen production from cheap and renewable resources has great potential to contribute to the supply of energy in the future. Moreover, it has an added advantage of waste management along with renewable energy generation. Among the various means of biological hydrogen production, the dark fermentation process has characteristic advantages such as it is independent of light, it can use a wide range of organic substrates, and it can be performed under ambient environmental conditions. In spite of its advantages, the dark fermentation process has low conversion efficiencies which limit its practical feasibility at the commercial scale. This chapter focuses on key principles behind the dark fermentative hydrogen production from organic substrates using mesophilic and thermophilic bacteria. The different metabolic pathways and enzymatic machinery involved in the facultative and obligate anaerobic bacteria are discussed in detail. Also, different approaches to enhance the hydrogen yields have been described with a specific emphasis on the effect of physicochemical operating conditions. Furthermore, the benefits and challenges of integrating dark fermentation with other technologies have been illustrated.
