Modeling of biogas production and biodegradability of date palm fruit wastes with different moisture contents

Abstract

Three mathematical models are implemented in this research to describe the hydrolysis kinetics and cumulative biogas production during the anaerobic digestion of wastes from date palm fruits. Kinetic modeling based on first-order, Gompertz, and surface-based models was performed to find out whether the controlling step is hydrolysis kinetics or bacterial growth. By using batch tests, the modeling was extended to include the digestion under mesophilic and thermophilic conditions at different blending fractions of 10, 15, 25, and 50% (weight of solid/weight of water) (w/w). The results showed that the highest and the lowest biogas yield were in the case of 15% w/w (182 L/kgVS) and the case of 50% w/w (84 L/kgVS), respectively. A 203 L/kgVS was the maximum biogas reached using recycled digestate wastes with 25% of the substrate content. The Gompertz model showed the best fit of these experiments’ results providing that bacterial growth is the limiting step in the generation of biogas from the wastes of date palm fruits. The maximum deviation between the model predictions and the experimental data was 6%, while the lowest deviation, 2%, was estimated in the case of 15% w/w.