Oleic Acid (C18:1) is an unsaturated Long Chain Fatty Acid (LCFA), described as
especially problematic in anaerobic digestion processes. In this work, a sludge heavily loaded with
5985 mgCOD.gVSˉ¹ was studied in terms of its capability to biodegrade oleic acid in batch assays,
in concentrations ranging from 100 to 1500 mg.lˉ¹. Lag phases before the onset of methane
production increased with the oleic acid concentration, up to 17 days for 1500 mg.lˉ¹and methane
production did not exceed 50% recovery for the highest concentrations tested (1000 and 1500
mg.lˉ¹). After the mineralization of the biomass-associated substrate, and for the same
concentration range, maximum lag phases of three days and methane recoveries up to 80% were
obtained, evidencing an improving capacity of the sludge to biodegrade oleic acid. Also the
specific methanogenic activity with acetate and H2/CO2 as individual substrates increased 3.6 and
2 times respectively, after the mineralization of the biomass associated substrate, confirming the
reversibility of the inhibitory effect of LCFA, even when the sludge was heavily loaded with more
than 5 g COD.gVSˉ¹.Fundação para a Ciência e a Tecnologia (FCT) - POCTI/CTA/46328/2002
