Evolution of control parameters in biochemical methane potential tests of olive mill solid waste (OMSW), thermal pre-treated OMSW, and its co-digestion with Dunaliella salina

Abstract

The aim of the present work was to compare the mesophilic anaerobic digestion of untreated olive mill solid waste (OMSW), soft hydrothermal pre-treated OMSW (SHP OMSW), and a co-digestion mixture of 95% OMSW and 5% microalga Dunaliella salina (co-OMSW). During the co-digestion experiment, the volatile fatty acid accumulation decreased in comparison with that obtained for OMSW and SHP OMSW, reducing the slight inhibition observed during the OMSW and SHP OMSW experiments. Final values of methane yield of 380 ± 1 mL CH4 g−1 VSadded for the OMSW, 424 ± 2 mL CH4 g−1 VSadded for the SHP OMSW, and 491 ± 1 mL CH4 g−1 VSadded for the co-OMSW were determined. Two mathematical models, first-order kinetics and modified Gompertz model, were employed to fit the experimental data with the aim of elucidating the anaerobic biodegradation and obtain the kinetic constants. Both models allowed for adequately fitting the experimental results of methane production with time. The kinetic constant, k, of the first-order model increased by 12% for the co-OMSW compared with the values achieved for OMSW and SHP OMSW. The modified Gompertz model revealed that the maximum methane production rate, Rm, for the co-OMSW and SHP OMSW increased by 34.7% and 10.3% compared with the value obtained for OMSW.