Characterization of Cynara cardunculus L. stalks and their suitability for biogas production

There is emerging interest in the production of biomethane as a biocombustible either through anaerobic digestion of biomass and/or energy crops. Cynara cardunculus L. is a crop with high biomass yields used in the production of bioenergy, with the seeds being used for biodiesel production and the remaining biomass used as solid fuel in biomass plants. This work aims to present results concerning the obtainable methane yield of Cynara stalks when submitted to anaerobic digestion, and the effects of selected pre-treatments (mechanical, thermal and thermochemical). For this purpose, two batch anaerobic digestion experiments (Trial I and Trial II) were performed. Minimum cumulative methane was achieved for the untreated substrate yielding 0.3 L CH4/g VS0. A maximum methane yield of 0.5–0.6 L CH4/g VS0 was achieved depending on the selected pre-treatment. Thermochemical pre-treatment using NaOH was revealed to be a very efficient hydrolysis method.

► The results achieved show that Cynara stalks are a good substrate for biogas and methane production in Mediterranean countries. ► Cynara stalks cumulative methane yield is higher than 0.3 L CH4/g VSadded depending on the pre-treatment applied. ► Mechanical and thermal pre-treatments with NaOH greatly improved VS reduction and cumulative methane yield.