Biological hydrogen production: Dark fermentation

Over the past few decades, the global population and the demand for energy have been growing at an exponential rate. Fossil fuels are the major source of energy (about 80%) in modern society (Demirbas, 2007). On the basis of the current consumption rate, it is estimated that the present known reserves of fossil fuels will last from 41 to 700 years (Goldemberg and Johansson, 2004; Goldemberg, 2007). The limited life and the unfettered use of fossil fuels and concerns about energy security have had a negative impact on the environment because of the emission of greenhouse gases (CO₂, CH₄, and CO), which has resulted in global warming and environmental pollution (Koh and Ghazoul, 2008; Saratale et al., 2008). For these reasons, in the present century, significant efforts are being made globally toward the development of technologies that generate clean, sustainable energy sources that can be a substitute for fossil fuels. One of these is biofuel (Gong et al., 1999; Ragauskas et al., 2006).