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 conduct ed 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 we re used as indicator of process efficiency. Counts of the main microbi al groups involved in methanogenesis were determined to study microorg anisms behaviour with different process conditions. The best COD remov al (70-80%) was obtained with 2 days retention time and organic load o f 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 proc ess was not inhibited. Acidogenic and methanogenic bacteria significat ively decreased, when the digester operated at high organic load.