Integrated treatment of olive oil mill effluents: Effect of chemical and physical pretreatment on anaerobic treatability

Difficulties met in the anaerobic treatment of olive oil mill effluents (OM E) suggest the use of a chemicophysical pretreatment for the removal of bio recalcitrant and/or inhibiting substances (essentially lipids and polypheno ls) as selectively as possible before anaerobic digestion. Laboratory scale experiments were carried out in order to identify pretreatment type and co nditions capable of optimizing OME anaerobic digestion in terms both of kin etics and methane yield. Ultrafiltration, even if it allowed very high remo vals of lipids and polyphenols, was affected by poor selectivity (indeed, l arge amounts of biodegradable COD were also removed). Centrifugation turned out to be preferable to sedimentation owing to smaller volumes of separate d phase. Results of great significance were obtained by adding Ca(OH)(2) (u p to pH 6.5) and 15 g/l of bentonite, and then feeding the mixture to the b iological treatment without providing an intermediate phase separation. Ind eed, the biodegradable matter adsorbed on the surface of bentonite was grad ually released during the biotreatability test, thus allowing the same meth ane yield (referred to the total COD contained in untreated OME) both in sc arsely diluted (1 : 1.5) pretreated OME and in very diluted (1 : 12) untrea ted OME. Application of a continuous process combining pretreatment (with C a(OH)(2) and bentonite) and anaerobic digestion without intermediate phase separation is suggested. (C) 1999 IAWQ Published by Elsevier Science Ltd. A ll rights reserved.