Microbial electricity driven anaerobic phenol degradation. Microbial electricity driven anaerobic phenol degradation in microbial electrochemical reactors

Microbial electrochemical technologies (MET) are promised to allow efficient removal of pollutants from different bodies of water and sediments. Thereby, removal of phenol, an industrial pollutant with high toxicity and persistence, was examined several times. Yet, due to contradicting previous research it is still undeciphered, if anaerobic phenol degradation using anodes as sole terminal electron acceptor is feasible. Here we provide strong indications for an anaerobic phenol degradation using microbial anodes by identifying key metabolites of the anaerobic pathway (4-hydroxybenzoic acid, benzoic acid). Furthermore, we demonstrate that the experimental design (one-chamber or two-chamber reactors, anode potential of +0.2 V or +0.4 V vs. SHE) has only a minor influence on phenol degradation. One-chamber reactors (+0.4 V) exhibited an average phenol removal rate of 3.5±0.2 mg L−1 d−1, two-chamber reactors showed 3.6±0.1 mg L−1 d−1 and 2.6±0.9 mg L−1 d−1 at anode potentials of +0.4 V and +0.2 V, respectively. The experimental design certainly influenced the microbial community leading presumably to different mechanisms for anaerobic phenol degradation. Geobacter and Arcobacter were enriched in two-chamber reactors, whereas the increased availability of cathodically produced H2 led to a dominance of sulfate-reducing microorganisms in one-chamber reactors. Interestingly, a phylotype affiliated to the genus Syntrophorhabdus that is known for syntrophic phenol degradation exhibited similar abundances in all experiments indicating its key role for anaerobic phenol degradation. Further studies, especially on single pure and co-cultures, are required for deciphering the food web of electricity driven anaerobic phenol degradation.