Enhanced dissimilatory perchlorate reduction in the presence of humic acids or 2,6-anthraquinone disulfonate as quinone redox mediators

Humic acids (HA) and anthraquinone-2,6-Disulfonate (AQDS) are conceived as quinone-based redox mediators (QRM) in contaminant transformation processes, however, their effects on perchlorate (ClO4-) reduction remain unclear. This study explored the efficacy of quinone-mediated perchlorate reduction and the redox reactions occurred in QRM-amended systems. Relative to the average perchlorate reduction rate (k) in the control system, k was increased by 1.8, 1.9, and 2.3-fold in the presence of 100 mg/L commercial HA, extracted HA, and AQDS, respectively. Moreover, in AQDS-amended systems, k was further increased by 66.3% and 158.6%, respectively, with the addition of 0.003 g and 0.032 g hematite to the 200 mL culture. The critical redox reactions implying the electron transferring mechanism were explored and proven to be enzymatically driven. The presence of AQDS shortened the nitrate-induced lag of perchlorate reduction by stimulating nitrate exhaustion rate (2.83 mM NO3- h(-1) compared to 1.26 mM NO3- h(-1) in the control). Also, the inhibition of the 5-h aeration was alleviated (36.6% compared to 52.5% in the control) due to the higher redox-buffer capacity in AQDS-amended systems. Thaeura was predominant in all perchlorate-acclimated inocula, while the presence of QRM contributed to the enrichment of Desulfuromonas and Geobacter.