| Summary: | Conductive materials (CM) improve the efficiency of methane production (MP) in anaerobic digestion (AD) processes (Martins et al. 2018), but little is known on the impact of CM directly on methanogens. Different species of methanogens were shown to be differentially affected by carbon nanotubes (CNT) (Salvador et al. 2017; Zhang, Zhang, and Lu 2018). For instance, CNT increased significantly the activity of an hydrogenotrophic methanogen (Methanobacterium formicicum) (Salvador et al. 2017), but other methanogenic species were less affected (Salvador et al. 2017; Zhang, Zhang, and Lu 2018). In this study, we evaluated the effect of other CM (activated carbon (AC) and magnetite (Mag), at 0.5 g/L) on the activity of both hydrogenotrophic (M. formicicum and Methanospirillum hungatei) and acetoclastic (Methanosarcina barkeri and Methanosaeta harundinacea) pure cultures of methanogens. The presence of AC resulted in reduced lag phases preceding the MP, and faster initial MP rates (IMPR), which was more evident in M. formicicum cultures (IMPR increased 15 times). Magnetite inhibited the activity of M. formicicum, and showed a minor impact in the activity of the other methanogens.
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