Enhanced Reactive Red 2 anaerobic degradation through improving electron transfer efficiency by nano-Fe3O4 modified granular activated carbon

Abstract

In this study, nano-Fe3O4 supporting on granular activated carbon (NFGAC) were prepared, characterized and used as an individual additive to promote the anaerobic digestion of azo dye Reactive Red 2 (RR2) wastewater. Results showed that organics removal and methane production were effectively promoted with the addition of NFGAC. Compared with the control reactor, the RR2 removal efficiency increased by 117.9% and the methane production increased by 167.2% in the 0.18-NFGAC added reactor when sole RR2 used as the substrates. Further analysis indicated that during the RR2 anaerobic digestion process the electron transfer system (ETS) activity was effectively improved with the addition of NFGAC. One of the possible mechanism was that the loading nano-Fe3O4 on the surface of GAC could increase the number of functional groups in NFGAC, which were beneficial to enhancing the electron accepting capacities (EAC) and electron donating capacities (EDC). Microbial community analysis showed that the bacteria (Halomonas, Pseudomonas and Bacillus) relevant to RR2 removal were enriched in NFGAC added reactors, which played an important role during RR2 removal process. In addition, the addition of NFGAC could promote potential direct interspecies electron transfer (DIET) between Pseudomonas and Methanosarcina.