Anaerobic oxidation of diclofenac coupled with dissimilatory iron reduction: Kinetics, mechanism, and microbial community function succession

Diclofenac (DCF) is frequently detected in the environments; however, the mechanisms for its anaerobic biodegradation coupled with dissimilatory iron reduction (DIR) are still unclear, particularly the key microbial community and function gene involved in this bioprocess have been rarely identified. The present study firstly demonstrated the microbial-mediated anaerobic oxidation of DCF coupled with DIR. 82.6 +/- 2.0 % of DCF (10.0 mg/L) was eliminated with a maximum rate constant (k) of 0.22 day(-1) during 90 days' incubation. The amorphous Fe(III) minerals and neutral pH (pH = 7.0) were critical to induce higher dissimilatory iron reducing bacteria (DIRB) availability for the anaerobic DCF biotransformation. DCF could undergo favorable oxidation through transferring electron between DCF and Fe-(III), while the hydroxylation of anilines and biotic cleavage of the C-N bond mainly contributed to the transformation. Paraclostridium, Ruminococcaceae_UCG-009, Prevotella_7 and Anaerofilu would be the main functional microorganisms, synergistically facilitating the DCF degradation. The kyoto encyclopedia of genes and genomes (KEGG) predictive functional profiling analysis showed that the effective improvement (16.94 %similar to 98.83 %) in the abundance of iron reduction-related genes was induced during the anaerobic bioprocess, thus potentially promoting the biotransformation of DCF. This study would provid a novel insight into the mechanism underlying the anaerobic biotransformation of DCF.