Synergistic effect of electrotrophic perchlorate reducing microorganisms and chemically modified electrodes for enhancing bioelectrochemical perchlorate removal.

Perchlorate has been described as an emerging pollutant that compromises water sources and human health. In this study, a new electrotrophic perchlorate reducing microorganism (EPRM) isolated from the Atacama Desert, Dechloromonas sp. CS-1, was evaluated for perchlorate removal in water in a bioelectrochemical reactor (BER) with a chemically modified electrode. BERs were operated for 17 days under batch mode conditions with an applied potential of -500 mV vs. Ag/AgCl. Surface analysis (i.e., SEM, XPS, FT-IR, RAMAN spectroscopy) on the modified electrode demonstrated heterogeneous transformation of the carbon fibers with the incorporation of nitrogen functional groups and the oxidation of the carbonaceous material. The BERs with the modified electrode and the presence of the EAM reached high cathodic efficiency (90.79 ± 9.157%) and removal rate (0.34 ± 0.007 mol m-3-day) compared with both control conditions. The observed catalytic enhancement of CS-1 was confirmed by a reduction in the charge transfer resistance obtained by electrochemical impedance spectroscopy (EIS). Finally, an electrochemical kinetic study revealed an eight-electron perchlorate bioreduction reaction at -638.33 ± 24.132 mV vs. Ag/AgCl. Therefore, our results show the synergistic effect of EPRM and chemically modified electrodes on perchlorate removal in a BER.

Bioprospecting for electrochemically active perchlorate-reducing microorganisms.

This study evaluated the electrochemical capacity of four perchlorate-reducing microorganisms (PRMs) isolated from an Altiplanic Andean watershed naturally pressured with perchlorate. Three-electrode electrochemical cells were used to test the electrochemical activity of the obtained isolates. Electrochemical evaluation (i.e., cyclic voltammetry, electrochemical impedance spectroscopy, chronoamperometry) revealed that two isolates identified as Dechloromonas sp. CS-1 and Clostridioides sp. CS-2 are electrochemically active PRMs. Bacterial isolates exhibiting cathodic peaks at -651 mV and -303 mV (vs. Ag/AgCl) for CS-1 and CS-2, respectively. Electrotrophic perchlorate removal was demonstrated by a 6-days chronoamperometry with removal rates of 27 and 17 mg L-1 day-1 and cathodic efficiencies of 93% and 45%, for CS-1 and CS-2, respectively. Chemical and electrochemical results suggest two different mechanisms of electrotrophic perchlorate removal, a complete eight-electron bio-reduction (i.e., perchlorate to chloride) for CS-1 and a partial two-electron bio-reduction (i.e., perchlorate to chlorate) for CS-2. The observed differences could be linked to their enzymatic differences, as in their membrane compositions. Thus, the results of this work increase the limited number of known electrotrophic microorganisms and expand the application of bioelectrochemical systems to develop new perchlorate treatment and remediation technologies.