Quantification of the inhibitory effect of methyl fluoride on methanogenesis in mesophilic anaerobic granular systems

The inhibitory effect of CH3F on methanogenesis in mesophilic anaerobic granules was tested at different concentrations (0–10% v/v, in the gas phase) and verified by the stable carbon isotopic signatures of CH4 and CO2. The results showed that the inhibitory effect increased with the initial CH3F concentration up to 5%. The CH3F concentration causing 50% metabolic inhibition was 0.32%. Complete inhibition of acetoclastic methanogenesis with a 91% reduction in total methanogenic activity was achieved when 5% CH3F was initially added to the headspace, which resulted in 870 μM dissolved CH3F in the liquid. It was much higher than that applied in other natural anoxic non-granular systems, indicating that the layered granular structure influenced the inhibitory effect. The obvious increase in hydrogen content indicated that high concentrations of CH3F (⩾5%) suppressed hydrogenotrophic methanogenesis as well. The stable inhibition lasted for at least 6 d as the CH3F concentration decreased slowly with incubation time. These results suggested that CH3F could be used for investigating methanogenic processes in anaerobic granular systems after the CH3F concentration and incubation time for specific inhibition of acetoclastic methanogenesis were carefully determined. In the present system, CH3F concentration of 5% was suggested to be optimal.

► Inhibition by CH3F for quantifying methanogenic pathways in granules was studied.
► The weakened inhibitory effect was possibly due to the layered granular structure.
► Hydrogenotrophic pathway was nonspecifically inhibited at high CH3F levels.
► CH3F concentration gradually decreased and methanogenesis recovered after 6 d.