Effects of nickel and cobalt on kinetics of methanol conversion by methanogenic sludge as assessed by on-line CH4 monitoring

When metals were added in a pulse mode to methylotrophic-methanogenic bioma ss, three methane production rate phases were recognized. Increased concent rations of Ni and Co accelerated the initial exponential and final arithmet ic increases in the methane production rate and reduced the temporary decre ase in the rate, When Ni and Co were added continuously, the temporary decr ease phase was eliminated and the exponential production rate increased. We hypothesize that the temporary decrease in the methane production rate and the final arithmetic increase in the methane production rate were due to m icronutrient limitations and that the precipitation-dissolution kinetics of metal sulfides may play a key role in the bioavailability of these compoun ds.