Previous works on the anaerobic treatment of olive oil mill effluents (OME) have shown that the inhibition of methane production is mainly caused by the presence of lipids. Saturation of unsaturated long-chain fatty acids (LCFAs) is the key factor to prevent inhibition of methanogenesis. This paper reports the experimentation carried out in a semi-continuous lab scale two-reactor system fed with diluted OME. Phase separation (acidogenesis and methanogenesis) was not complete in the two reactors. Indeed, a moderate methanogenic activity was allowed to be established in the first reactor. This scheme proved to be suitable to obtain an almost quantitative biotransformation of unsaturated LCFAs to palmitic acid in the first reactor, thus drastically lowering lipid inhibition on methanogenesis in the second reactor. The addition of an easily biodegradable substrate such as glucose did not improve biodegradation of polyphenols. A continuous flushing of N2/CO2 through the ‘acidogenic’ reactor did not promote the β-oxidation of palmitic acid. The two-reactor system with partial phase separation could find useful application for the anaerobic treatment of any lipid-containing wastewater.

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