Generation, utilization, and transformation of cathode electrons for bioreduction of Fe(III)EDTA in a biofilm electrode reactor related to NO_x removal from flue gas

A chemical absorption-biological reduction (CABR) integrated system, which employs iron chelate as a solvent, is under development for NO_x removal from flue gas. Biofilm electrode reactor (BER) is deemed as a promising bioreactor to regenerate the iron chelate. Although it has been proved that BER can significantly enhance the bioreduction of Fe(III)EDTA, the bioelectrochemistry mechanism involved in the bioreduction of Fe(III)EDTA remains unknown. This work aims to explore this mechanism via the analysis of the generation, utilization, and transformation of cathode electrons in the BER. The results indicate that the generation of cathode electrons follows Faradays law. The generated cathode electrons were used to produce H₂ and directly reduce Fe(III)EDTA in the BER. Meanwhile, the produced H₂ served as an electron donor for bioreduction of Fe(III)EDTA. The excess H₂ product was transformed to simple organics, e.g., methanol by the hydrogen autotrophy of Pseudomonas under the inorganic and anaerobic conditions. Overall, this work revealed that the reduction of Fe(III)EDTA in the BER was enhanced by both direct electrochemical reduction and indirect bioreduction using H₂ as an intermediate. It is also interesting that the excess H₂ product was transformed to methanol for microbial metabolism and energy storage in the BER.