Olive Mill Wastewater Anaerobically Digested: Phenolic Compounds with Antiradical Activity

The recovery of phenolic compounds, present in the olive fruits and its by-products, has been intensively studied by the antioxidant properties. Olive mill wastewater (OMW) is a phenolic-rich industrial effluent that can be advantageously valorized by the anaerobic digestion to the methane and agricultural fertilizer productions. The objective of this work was to evaluate the antiradical activity of OMW after anaerobic digestion in order to maximize the valorization of this type of effluents. The digested flow was obtained from an anaerobic hybrid reactor treating OMW at different organic loading rates (OLR), from 3.3 to 7.1 kg COD m(3) d(-1). OLR rise was applied by increasing progressively the OMW volume fraction from 8 % to 83 % in the feed mixture. The input and output streams, obtained at different OMW volume fractions, were characterized in terms of antiradical activity and phenolic compounds identification and quantification. Despite of the fraction decrease on total phenolic compounds provided by OMW anaerobic digestion, the antiradical activity is still significantly high (EC50 = 3.24) in the digested effluent. Oleuropein was the main phenolic compound present in the substrate before and after anaerobic digestion (about 15 % of the initial value). Others phenolic compounds present are: gallic acid, hydroxytyrosol, tyrosol, and quercetin. These data confirmed that, after the OMW anaerobic treatment to produce biomethane, the remaining flow yet contain useful compounds with antiradical activity.