Kinetic study of anaerobic digestion of olive mill wastewater previously fermented with Aspergillus terreus

Abstract

A kinetic study has been made of the anaerobic digestion of olive mill wastewater previously fermented with Aspergillus terreus. The anaerobic process was carried out in a digester 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 = G m [1—exp (− K A t)], from which the apparent kinetic constant, K A, was calculated. The kinetic constant was found to be scarcely influenced by the substrate concentration over the studied COD (chemical oxygen demand) range (viz. 3·9–8·8 g/litre). Its mean value was 1·45 days −1. This value 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 and the total phenolic compound content (analysed by high performance liquid chromatography HPLC) were reduced by 86·8 and 94·3% respectively as a result of the pretreatment. Finally, the average COD fraction removal was around 70% and the yield coefficient was 349 ml CH 4 STP/g COD, viz. 30% higher than that provided by untreated wastewater.