Generation of biogas using crude glycerin from biodiesel production as a supplement to cattle slurry

The influence of crude glycerin on biogas production and methane content of the produced biogas was studied, when added to cattle slurry. The experimental design consisted of 5% wt (Gli 5), 10% wt (Gli 10), and 15% wt (Gli 15) of crude glycerin added to cattle slurry, and one control digester without addition of crude glycerin. Anaerobic digestion was carried out in 4 laboratory size CSTR-type biogas digesters with a working volume of 3 L, in semi-continuous regime at mesophilic conditions, over a period of 10 weeks. The highest biogas yields (825.3 mL g−1 and 825.7 mL g−1, respectively) relative to mass of volatile compounds added, were produced by the treatments Gli 5 and Gli 10. The control treatment produced 268.6 mL g−1, whereas the treatment Gli 15 produced 387.9 mL g−1. This low value was due to the breakdown of the process. Compared to the control, methane contents was increased by 9.5%, 14.3%, and 14.6%, respectively, for the treatments Gli 5, Gli 10, and Gli 15.