Bioelectrochemical systems as tools to steer anaerobic digestion processes

摘要

Exoelectrogenic microorganisms have the ability to couple the oxidation of organic or inorganic electron donors to the transfer of electrons onto an anode surface. Hence, the organisms can catalyze the direct conversion of chemical energy into electrical energy. They typically use fermentation end products such as acetate as electron donors. The kinetics of the electron transfer process are dependent on the potential of the electrode. In other words, it is possible to control the respiratory and the substrate conversion rates via the working electrode potential. Here, we show that such a microbial anode can be used to steer anaerobic digestion processes. We constructed a model biogas reactor fed with corn silage in which we implemented microbial anodes based on carbon. Our data show that we can stoichiometrically steer methane production of the reactor by applying a suitable potential to the carbon electrodes. This allows overcoming process imbalances during the biogas process in which volatile fatty acids accumulate in the biogas reactor. Moreover, we can show that it is possible to use a bioelectrochemical system as a tool in a biorefinery process. Here, we fed the microbial anode with a dark fermentation plant percolate containing acetate, butyrate and propionate as organic carbon sources. This way, we were able to remove acetate and butyrate while propionate was not oxidized. It is possible to use the remaining propionate for a subsequent biotechnological process to produce the valuable platform chemical acetoin. Hence, it was possible to establish a biotechnological process for the conversion of biogenic residual and waste streams into valuable platform chemicals.