Simultaneous CO 2 and CO methanation using microbes

ABSTRACT In this study, we developed a method for simultaneous bio-methanation of CO 2 and CO with H 2 in a single bioreactor using a combination of carboxydotrophic bacteria and methanogenic archaea for industrial applications. Methanogenic archaea generally use H 2 and CO 2 to produce methane, whereas very few methanogenic archaea methanize CO, and these grow slowly and consequently produce low reactant gas turnover rates. Thus, to achieve fast and simultaneous transformation of CO and CO 2 , we identified a combination of carboxydotrophic and hydrogenogenic bacteria and methanogenic archaea that can produce H 2 and CO 2 from CO, and then methanize CO 2 and H 2 . The present screening experiments identified carboxydotrophic bacteria and methanogenic archaea that can cohabitate at the same thermophilic temperature and pH ranges and in the same growth medium. In these experiments, combinations of Carboxydocella thermautotrophica (DSM 12326), Carboxydocella sporoproducens (DSM 16521), and three thermophilic rod-shaped methanogenic archaeal cultures from MicroPyros GmbH formed unique microbial co-cultures that transformed CO 2 , H 2 , and CO to methane. The successful combination of these microbes could be used to gasify biowastes, such as sewage sludge, as alternative sources of hydrogen for microbial power-to-gas processes. Accordingly, gasification under these conditions produced H 2 -rich gas containing CO 2 and CO, theoretically allowing various types of biowastes to be converted to biomethane, which is CO 2 -neutral, storable, and widely applicable as an energy source.