INTERACTION BETWEEN ACIDOGENESIS AND METHANOGENESIS IN THE ANAEROBIC TREATMENT OF OLIVE OIL MILL EFFLUENTS

The treatment of olive oil mill effluents (OME), even when performed w ith the most appropriate technology (i.e. anaerobic digestion) meets g reat difficulties in reaching the depuration efficiencies required by national regulations all over the Mediterranean area. This paper was a imed at gaining better insight into the degradation of the main compou nds contained in the OME; in particular, the interaction between the t wo successive stages occurring in the anaerobic digestion, the acidoge nesis and the methanogenesis, was investigated. First of all, the best operating conditions were identified. Most of the lipids were degrade d both in acidogenesis and methanogenesis tests. On the other hand, po lyphenol-like substances were not degraded at all in acidogenic condit ions, whereas they were partially removed in methanogenic conditions. A little methanogenic activity, established in acidogenic conditions b ecause of the partial degradation of the chemical inhibitor, seems to be the key factor determining lipids degradation even in acidogenesis tests. Synthetic solutions were also tested. Oleic acid was degraded b oth in acidogenesis and methanogenesis tests, provided that an easily biodegradable substrate (glucose) was added to the solution. The prese nce of glucose was also required for the degradation of p-hydroxybenzo ic acid in methanogenic conditions. This acid was not degraded at all in acidogenic conditions, thus confirming the results obtained in the tests on OME. Even if slightly lower, bioconversion yields of OME in a cidogenesis are remarkably less sensitive to the effect of pH and subs trate conditions than in methanogenesis. This result suggests that a t wo-phase anaerobic digestion might be adopted as a suitable process fo r optimizing OME degradation.