Anaerobic digestion of olive mill wastewater pretreated with Azotobacter chroococcum

Abstract

Abstract We carried out a kinetic study of the anaerobic digestion of olive mill wastewater that was previously fermented with Azotobacter chroococcum. The process was carried out batchwise in a bioreactor containing sepiolite as support for the mediating bacteria. The anaerobic digestion process was found to follow first-order kinetics and the experimental methane volume (G)-time (t) data to conform to an equation of the form G=Gm[1−exp(−K0t)], from which the apparent rate constant, Ko, was calculated. This kinetic constant (average value 1.21 day−1) was found to be scarcely influenced by the substrate concentration over the studied COD range (viz. 4.2−8.5 g/l). The specific rate of methane production was substantially higher than that obtained in the anaerobic digestion of untreated olive mill wastewater, and the process seemingly involved no inhibition phenomena as the biotoxicity of the waste was reduced by 30% as a result of the pretreatment. Finally, the average COD fraction removal was 73% and the yield coefficient was 313 ml CH4 STP/g COD.