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

The inhibitory effect of CH(3)F 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 CH(4) and CO(2). The results showed that the inhibitory effect increased with the initial CH(3)F concentration up to 5%. The CH(3)F 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% CH(3)F was initially added to the headspace, which resulted in 870 μM dissolved CH(3)F 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 CH(3)F (≥5%) suppressed hydrogenotrophic methanogenesis as well. The stable inhibition lasted for at least 6d as the CH(3)F concentration decreased slowly with incubation time. These results suggested that CH(3)F could be used for investigating methanogenic processes in anaerobic granular systems after the CH(3)F concentration and incubation time for specific inhibition of acetoclastic methanogenesis were carefully determined. In the present system, CH(3)F concentration of 5% was suggested to be optimal.