Integrated treatment of olive oil mill wastewater (OME): study of ozonation coupled with anaerobic digestion

The possibility of coupling a chemical treatment (ozonation) with a biological treatment (anaerobic digestion), is investigated for olive oil mill effluents (OME). Preliminary tests showed that both total phenols and unsaturated lipids are reduced to about 50% in 3 h of ozonation and that the total COD remains about unvaried. Nevertheless ozonated OME exhibit in general a longer lag phase and a lower yield in methane than OME themselves. These effects are more evident at higher OME concentrations. Methanogenic tests were also conducted on OME samples to which oleic acid or p-hydroxybenzoic acid and their ozonation products were added. Results indicate that the ozonation products of oleic acid are more inhibitory than the original substrate. The inhibitory effects of p-hydroxybenzoic acid (pHBA) and its ozonation products show a different dependence upon concentration: inhibition of ozonation products is remarkable at lower concentration but it increases more slowly as concentration increases. No effect of ozonation is observed on the acidogenic step of fermentation.