Effects of biomass densification on anaerobic digestion for biogas production

In order to elucidate the possibility of applying biomass densification in anaerobic digestion, pelleting and briquetting were typically investigated for biogas production, and the anaerobic digestion using densified biomass at higher solid content was discussed as well. In addition, the logistic cost, including harvest, transportation, and storage, was also evaluated to check the economic feasibility once biomass densification was employed for biogas production. The results demonstrated that the main composition, including cellulose, hemicellulose and lignin, of the pelleted and briquetted corn stover exhibited some degradation compared with their corresponding undensified corn stover. Both pellets and briquettes had no adverse impacts on anaerobic digestion. The cumulative biogas production from pellets was 349.9 mL g⁻¹ VS (VS: volatile solid), which was 25.8% higher than unpelleted corn stover (278.1 mL g⁻¹ VS, respectively), moreover, the cumulative CH₄ production from pellets was 185.7 mL g⁻¹ VS compared with 135.1 mL g⁻¹ VS of unpelleted corn stover. Biogas production from briquettes was also slightly higher than that of the unbriquetted corn stover, however, improvement was not statistically significant. Increasing the organic loading, relatively higher biogas and CH₄ production can be achieved from briquettes compared with the unbriquetted corn stover. This was mainly attributed to more free water in the anaerobic digestion of briquettes. Especially, there was 11.7% improvement on biogas production as the organic loading was increased to 80 g TS per kg (TS: total solid). As the briquettes were employed for biogas production with the digestor scale of 3000 m³, the logistic cost could be curtailed by 36.1%. Evidently, the biomass densification can be employed in anaerobic digestion for biogas production to potentially solve the extra high cost of logistic issues.