Anaerobic digestion of olive mill effluents : microbiological and processing aspects

Olive mill effluents have been treated by anaerobic digestion, using a laboratory scale, fixed bed, upflow digester. The process was conducted with two different retention times (2 and 1 days); organic load was increased up to 40 kg COD/m(3)d. COD removal and biogas production were used as indicator of process efficiency. Counts of the main microbial groups involved in methanogenesis were determined to study microorganisms behaviour with different process conditions. The best COD removal (70-80%) was obtained with 2 days retention time and organic load of 5.5-9.5 kg COD/m(3)d By working with an organic load of 40 kg COD/m(3)d at 1 day retention time, plant performances decreased but the process was not inhibited.