AUTHOR=Kubannek Fabian , Moß Christopher , Huber Katharina , Overmann Jörg , Schröder Uwe , Krewer Ulrike 

TITLE=Concentration Pulse Method for the Investigation of Transformation Pathways in a Glycerol-Fed Bioelectrochemical System

JOURNAL=Frontiers in Energy Research

VOLUME=6

YEAR=2018

URL=https://www.frontiersin.org/journals/energy-research/articles/10.3389/fenrg.2018.00125

DOI=10.3389/fenrg.2018.00125

ISSN=2296-598X

ABSTRACT=<p>We investigated transformation pathways and determined rate constants in a continuously operated glycerol-fed bioelectrochemical system under chemostatic conditions by applying concentration pulses of various intermediates. Our methodology does not require the interruption of the continuous operation and is thus in principle suitable for elucidating processes in continuously operated bioreactors in industry as well as in laboratory studies. Specifically for the example of glycerol electrooxidation, pulse responses of current density and effluent concentrations reveal that glycerol is first fermented to acetate, which is then oxidized electrochemically by the anode respiring bacteria. Microbial community analysis confirms this division of labor with a bioanode dominated by <italic>Geobacter</italic> species (92.8%) and a much more diverse fermenting community in the planktonic phase, containing mainly <italic>Desulfovibrio</italic> sp. (45.2%) and <italic>Spiroaetales</italic> (18.1%). <italic>Desulfovibrio</italic> and <italic>Geobacter</italic> species are identified as promising candidates for tailored communities for glycerol electro-oxidation. From an acetate concentration pulse experiment, growth rates and half saturation rate constants for the biofilm of 1.4 mol m<sup>-3</sup> and 933 mmol m<sup>-2</sup>d<sup>-2</sup> are obtained, respectively. Furthermore, 1,3-propanediol and glycerol concentration pulse experiments show that the reaction from glycerol to 1,3-propanediol is reversed at high 1,3-propanediol concentrations. The presented methodology allows one to study pathways and extract rate constants through simple experiments in a running system without irreversibly altering the microbial community or destroying the biofilm.</p>