Kinetics of mesophilic anaerobic digestion of the two-phase olive mill solid waste

Abstract

A kinetic study of the anaerobic digestion of two-phase olive mill solid waste (OMSW) was carried out in a laboratory-scale completely stirred tank reactor at mesophilic temperature (35 °C). The reactor was operated at three different feed substrate concentrations: 34.5, 81.1 and 113.1 g COD/l. The hydraulic retention time (HRT) varied between 40.0 and 8.3 days for the first feed used and between 50 and 10 days for the other two feed substrate concentrations. The results were evaluated using the Chen–Hashimoto methane production model to determine the kinetic constants of the process. The kinetic constants ( μ max and K) were affected by the feed substrate concentration and decreased by 63 and 65%, respectively, when the feed concentration increased from 34.5 to 113.1 g COD/l. This behaviour is believed to be due to the higher levels of phenolic compounds and biotoxicity present in the most concentrated substrate used. Methane production was reproducible within 10% deviations.