THE EFFECTS OF THE MOST IMPORTANT PHENOLIC CONSTITUENTS OF OLIVE MILLWASTE-WATER ON BATCH ANAEROBIC METHANOGENESIS

The most important phenolic constituents of Olive Mill Wastewater (OMW ), i.e. tyrosol, oleuropein and caffeic, p- hydroxybenzoic and protoca techuic acids, were added at various concentrations to aliquots of dom estic anaerobic sludge in Hungate serum bottles and these were incubat ed at 35 degrees C. The concentration of methane in the headspace gas was monitored to determine if the phenolics were fermented to methane or if they inhibited the anaerobic process. Only tyrosol and p- hydrox ybenzoic add were fermented to methane. At 600 mg l(-1) (but not at 40 0 mgl(-1)) oleuropein reduced the rate and the amount of methane produ ced. The ortho-diphenols (caffeic and protocatechuic acids) were inhib itory at 1000 mg l(-4) but not at 500 mg l(-1). In cultures supplement ed with acetic and propionic acids (VFA), and in unsupplemented cultur es, tyrosol at concentrations up to 600 mg l(-1) was fermented to meth ane. Between 900 and 1300 mg l(-1) tyrosol methane production was neit her enhanced nor inhibited relative to control cultures containing no tyrosol. Inhibition of methane production was evident when tyrosol was present at greater than or equal to 2000 mg l(-1). In similar experim ents with p-hydroxybenzoic acid enhanced methane production was observ ed at concentrations of less than or equal to 500 mg l(-1); no enhance ment or inhibition was observed at 700 mg l(-1); and inhibition was no ted when p-hydroxybenzoic acid was present at greater than or equal to 1000 mg l(-1).