Effect of cobalt on the anaerobic thermophilic conversion of methanol

AbstractThe importance of cobalt on the anaerobic conversion of methanol under thermophilic conditions was studied in three parallel lab‐scale UASB‐reactors and in cobalt‐limited enriched cultures. Reactors R1, R2, and R3 were fed with methanol in a bicarbonate‐buffered medium, supplied with iron and macronutrients: in R1 all metals were supplied (control), R2 was cobalt deprived, and in R3 all metals were deprived. In the 136 days of continuous experiment, a drop in performance was observed over the last 30 days. Particularly in R3, both methanol removal and methane formation dropped by 7.1% and 13.7%, respectively, compared to the control reactor, R1. When the medium was cobalt‐deprived, acetate was not produced and, as a consequence, the enriched consortium lost its capacity to degrade acetate, indicating that the acetotrophic microorganisms were washed out. The addition of 0.5 μM of cobalt to a cobalt‐deprived enrichment culture led to acetate accumulation. The results obtained in this study indicate that the mixed consortium requires a proper amount of cobalt, and its addition to a concentration of 0.1 μM leads to the highest methanol conversion rate, with methane as the sole end product from methanol. © 2004 Wiley Periodicals, Inc.