Increasing biological H2 production by employment of microbial electrolysis cells

Hydrogen (H2) is considered to be an important energy carrier in the near future. Biological H2 production represents a promising way for sustainable H2 production. Nevertheless, it is still in its infancies and faces some challenges. In this thesis five different approaches are pursued to increase H2 production using dark fermentation (DF) and microbial electrolysis cells (MECs). The first approach is the search for highly productive dark fermentative H2 producers by a meta-data analysis of existing literature on DF. Here bacteria of the taxonomic families Thermococcaceae, Clostridiaceae and Enterobacteriaceae were identified as promising candidates. The second approach is the use of extremophilic archaea for dark fermentative H2 production (DFHP). It could be shown, that the Crenarchaeon Desulfurococcus amylolyticus is able to use formate as substrate for microbial growth. The third approach is the use of a co-culture to increase H2 production. With a co-culture of Enterobacter aerogenes and Clostridium acetobutylicum and a H2 yield of 5.6 mol mol-1 glucose the Thauer limit of 4 mol mol-1 glucose was even exceeded. The fourth approach is the use of a MEC. Using the same co-culture as in the third approach, the beneficial effects of an applied voltage to the biological system could be shown. The fifth approach aimed to reduce unwanted side reactions in MECs. H2 consuming homoacetogenic bacteria were shown to decrease H2 production. A reduction of the H2 partial pressure by nitrogen sparging was shown to be one possible solution for this problem. These five approaches lead towards feasible biological H2 production systems and may help to prepare DFHP and MECs to large scale applications and industrial use. (author)