Effect of monensin and 2-bromoethanesulfonic acid on fatty acid metabolism and methane production from cattle manure

Summary The effect of monensin and 2-bromoethanesulfonic acid (BESA) on methane production from cattle manure and on volatile fatty acids metabolism was tested. At 10 days retention time 0.81 biogas per liter cattle manure and day were produced. Methanogenesis was inhibited 20% by 3 mM BESA per liter and 45% by 2–5 mg monensin per liter. When the digestion was inhibited with either of the both drugs, the acetate pool increased drastically. Like in untreated fermentations the propionate pool increased in BESA-inhibited fermentations for several hours after substrate addition. After 24 h however it did not decrease to the low level reached in non-inhibited fermentations. When monensin was the inhibitor, the propionate pool did not change for 15 h, but then decreased with the same rate as in the control experiment. Adaptation processes or detoxification may be responsible for the delayed degradation.The degradation of low concentrations of buty-rate to acetate and the turn over rates of the butyrate pool are almost identical in cattle manure containing BESA, monensin, or no inhibitor. The turn over of ¹⁴C-acetate from butyrate degradation is delayed in BESA and monensin inhibited fermentations.From the data presented it can be concluded, that BESA mainly inhibits the methanogens, while monensin seems to inhibit both, methanogenic and nonmethanogenic organisms. However, a fast adaptation to or detoxification of the antibiotic seems to occur.