Anaerobic biodegradation of oleate by a highly loaded biomass before and after degrading the associated substrate

Abstract

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.