Abatement of long-chain fatty acid inhibition of methanogenesis by calcium addition

Abstract Long-chain fatty acids are versatile inhibitors for methanogenic bacteria. Research concerning lauric acid toxicity proved that addition of calcium chloride can reverse lauric acid inhibition of methanogenesis, provided the addition is applied within several minutes after the inhibitory lauric acid concentration has entered the methanogenic environment. The antagonistic effect of calcium chloride is caused by precipitation of the inhibitory long-chain fatty acids as calcium salts. It has been proved that lauric acid has a strong affinity for methanogenic sludge. The rapid reaction of lauric acid with methanogenic sludge causes the need for almost immediate addition of calcium chloride to prevent inhibition of methanogenesis. Of the methanogenic potential of granular sludge 50% was lost after only 7·5 min of exposure. Addition of calcium chloride after an exposure period of 6 h had no effect at all.