1.1 Equipment

An anaerobic reactor with a working volume of 1 litre equipped with magnetic stirring and placed in a thermostatic chamber at 35 °C was used. The reactor had an upper settling zone designed to minimize loss of the biomass responsible for the process. The reactor was fed daily by means of an external feeder and liquid effluent removed daily through a hydraulic seal, comprising 25 cm liquid column, designed to prevent air from entering the reactor and biogas from leaving. This reactor has been described in detail elsewhere (Martin et al., 1991).

The methane volume produced in the process was measured using a 5 litre Mariotte reservoir fitted to the reactor. A tightly closed bubbler containing a NaOH solution (3 M) to collect the CO2 produced in the process was intercalated between the two elements. The methane produced displaced a given volume of water from the reservoir, allowing ready determination of the gas (Martin et al., 1991).

1.2 Inoculum

The reactor was inoculated with methanogenically active biomass from a laboratory-scale anaerobic reactor processing olive mill wastewater. The composition and features of the biomass used were: pH, 7.2; total solids (TS), 60.3 g/L; mineral solids (MS), 19.3 g/L; volatile solids (VS), 41.0 g/L; total suspended solids (TSS), 59.9 g/L; mineral suspended solids (MSS), 18.8 g/L; volatile suspended solids (VSS), 41.1 g/L.