Enhancement of the anaerobic digestion of olive mill wastewater by the removal of phenolic inhibitors

Abstract

Olive mill wasterwater (OMW) has a high organic pollutant load (45–130 g COD/litre) including various phenolic compounds, of which caffeic acid, thyrosol and hydroxythyrosol occur in the highest proportions. These two features make it impossible to purify OMW anaerobically unless a prior dilution is effected. Partial removal of some of the organic matter and phenolic compounds, by aerobic pretreatment with Geotrichum candidum is described. This provides a partially purified effluent that, for the same COD level as that of the original OMW, is degraded anaerobically more rapidly than original OMW as a result of the increase in methanogenic activity by 39 ml CH 4 STP /g VSS day for a COD of 7 g /litre. Finally, the presence of a sepiolite support (Pansil) in the digestors is shown to increase the biodegradability of the OMWs and the yield coefficient of the product (Y p).