COMPARATIVE EFFECT OF DIFFERENT AEROBIC PRETREATMENTS ON THE KINETICSAND MACROENERGETIC PARAMETERS OF ANAEROBIC-DIGESTION OF OLIVE MILL WASTE-WATER IN CONTINUOUS-MODE

A comparative kinetic study was carried out on the anaerobic digestion of olive mill wastewater (OMW) and OMW that was previously fermented with Geotrichum candidum, Azotobacter chroococcum and Aspergillus terr eus. The reactors used were continuously fed and contained sepiolite a s support for the mediating bacteria. A kinetic model for multicompone nt substrate removal by anaerobic digestion has been used. The model i s based on the linear removal concept which is a special case of the b roader Monod equation. The second-order kinetic constant, k(2)(s), was found to be influenced by the pretreatment carried out, and was 4.2, 4.0 and 2.5 times higher for Aspergillus, Azotobacter and Geotrichum-p retreated OMWs than that obtained in the anaerobic digestion of untrea ted OMW. This was significant at 95% confidence level. This behaviour is believed to be due to the lower levels of phenolic compounds and bi otoxicity present in the pretreated OMWs. In fact, the kinetic constan t increased when the phenolic compound content and biotoxicity of the pretreated OMWs decreased. In addition, the macro-energetic parameters of the anaerobic digestion of OMW, i.e. the specific rate of substrat e uptake for cell maintenance, m, and the yield coefficient for the bi omass, Y, decreased by a factor of 2.4, 3.6 and 5.1 and increased by a factor of 1.9, 2.2 and 2.4 respectively, for the OMWs previously trea ted with Geotrichum candidum, Azotobacter chroococcum and Aspergillus terreus in relation to the observed values for the untreated OMW.