Similar to CoCl2, pulse addition of vitamin B12 also supplied enough cobalt to maintain full methanol degradation during more than 35 days after the pulse. However, the specific methanogenic activities (SMAs) of the sludge in the vitamin B12 supplied reactor were around 3 times higher than the SMA of the sludge from the CoCl2 supplied reactor at the same sampling times, indicating that vitamin B12 may be playing a role more significant than the one of being just a cobalt source.