Modeling of sludge and flax anaerobic co-digestion based on combination of first order and modified Gompertz models: influence of C/N ratio and headspace gas volume
Résumé
The goal of this study is to improve biogas yields from the co-digestion of primary sludge (PS)
and flax, based on their carbon-to-nitrogen (C/N) ratio, and the effects of the headspace gas vol-
ume fraction (HSVF) in the batch reactor. The work was carried out in two stages. First, five mix-
tures of PS and flax at different C/N ratios were prepared for biogas production. The highest biogas
production was observed at a C/N ratio of 20, and the lowest at a C/N ratio of 10. In the second
stage, the optimum C/N ratio of 20 was used in batch reactor experiments to test five different
HSVFs. The highest biogas productions were obtained at an HSVF of 2.33. However, the high-
est methane content was recorded at an HSVF of 1.5 (62.33%). The theoretical and stoichiometric
methane yields of the feedstock used were estimated. Biochemical Methane Potential (BMP) tests
showed the presence of two fractions: one immediately biodegradable to methane and another, less
biodegradable, which required a lag phase to transform into biogas. A new kinetic model repre-
senting these two phases was proposed to accurately describe the results of the experiment.