Extracellular electron transfer of biocathodes: Revealing the potentials for nitrate and nitrite reduction of denitrifying microbiomes dominated by Thiobacillus sp.

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The use of biocathodes in bioelectrochemical systems (BES) for the removal of nitrate in wastewater has become a vital field of research. However, the elucidation of the underlying extracellular electron transfer (EET) fundamentals of denitrifying biocathodes is still lacking, but required for a deeper BES understanding and engineering. This study reports for the first time on the thermodynamics of microbial cathodes for nitrate and nitrite reductions using microbial microcosms isolated from a running denitrifying BES. Cyclic voltammetry showed that nitrate and nitrite reduction proceed at - 0.30 V, and - 0.70 V vs. Ag/AgCl, respectively, by surface associated EET sites. The biocathodes were predominantly covered by Thiobacillus sp. contributing with a nitrate reductase (narG) to the major function of the microcosms. In conclusion, the EET characteristics of denitrifying biocathodes are demonstrated for the first time ​
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