Role of Lipids and Phenolic Compounds in the Anaerobic Treatment of Olive Oil Mill Effluents

Abstract

The inhibitory effects of olive oil mill effluents (OME) on methanogenesis were studied by using p-hydroxybenzoic acid (HBA) and oleic acid (OA) as model compounds for phenolic compounds and lipids respectively. The addition of HBA (0.3 g l⁻¹) to diluted OME (5.7 g COD l⁻¹) had a negligible effect on methanogenesis in terms of kinetics and final methane yield. Strong inhibition was observed only at high HBA concentrations (6 g l⁻¹). The OA inhibited methane production much more strongly. Indeed, 0.35 g l⁻¹ of OA were able to double the lag phase for methanogenesis from diluted OME. With both compounds, the presence of an easily biodegradable co-substrate (glucose) did not increase the rate of substrate degradation nor methane formation. OME acidogenesis was significantly less sensitive than methanogenesis to the inhibitory effects exerted by OA and HBA, even at relatively high concentrations of the model compounds.