Process for production of methane by anerobic fermentation

Claim 1

In a process for production of biogas containing methane by anaerobic fermentation, under conventional fermentation conditions, of a fermentation medium comprised of an organic substrate of animal, vegetable or industrial origin, said medium being rich in at least one of cellulose, hemicellulose or lignocellulose, the improvement which comprises adding to said fermentation medium, between 0.001 and 0.35 millimoles per liter of fermentation medium, of at least one unsaturated fatty acid or ester thereof, wherein said fatty acid is selected from the group consisting of: linoleic acid, linolenic acid, arachidonic acid, clupanodonic acid, acids from linseed oil, esters of said acids and mixtures of said acids and wherein the yield of said biogas containing methane is at least 114% of that obtained without said fatty acid after a fermentation period of 30 days.