Enhancement of brown algae of the Ionian sea through the anaerobic digestion process

The growing demand for fossil fuels, combined with the uncertainty in their supply and the rapid increase in oil prices, has stimulated the search for sustainable alternatives linked to the use of biomass, such as macroalgae. In this research work, a sample of algae composed of a mix of Dictoma and Cystoseira (DC sample) was collected on the beach of Crotone (Italy) to evaluate, for the first time, its Biochemical Methane Potential (BMP) through anaerobic digestion process. The Dictoma–Cystoseira sample was characterized in terms of carbohydrates, proteins, lipids, carbon, nitrogen, total solids (TS), volatile solids (VS), moisture and ashes. The thermal and chemical properties of the Dictoma–Cystoseira sample have been investigated using X-ray diffractometry and Fourier-transform infrared spectroscopy. The BMP was evaluated after 20 days by an automated methane potential system test (AMPTS® II). Three kinetic models, such as the First order kinetic Model, Logistic function, and modified Gompertz Model, were used to find the kinetic parameters. The analyzed sample turns out to be composed of (37.90 ± 0.78) % of carbohydrates, (5.68 ± 0.23) % of proteins, (0.30 ± 0.01) % of lipids, C/N ratio equal to 36.37, (88.29 ± 1.84) % of TS, (35.13 ± 0.55) % of VS, (53.16 ± 1.93) % of ashes. The Theoretical Biochemical Methane Potential (BMPth) of this sample was 475.53 NmL/gVS. The experimental BMP (BMPex) was 87.03 ± 5.89 Nml/gLVS. The low yield is due to the high C/N ratio and the high ash content, i.e. inorganic material.