Study of anaerobic co-digestion of crude glycerol and swine manure for the production of biogas

Abstract

Crude glycerol and swine manure are large-scale effluents produced by the biodiesel industry and swine breeding, respectively. The use of such effluents for the production of biogas would contribute to increase the supply of renewable fuels and to decrease emissions of greenhouse gases. The present study evaluated the production of biogas from the anaerobic co-digestion of crude glycerol with swine manure through the use of response surface methodology (RSM). A central composite design was employed with two factors, four axial points and four central points. The two factors evaluated were crude glycerol and swine manure concentrations, which were examined in the range of 4 to 10 g L-1 and 5 to 15 g L-1, respectively. Activated sludge obtained from an urban sewage treatment plant was used as inoculum. The carbon:nitrogen ratio (C/N) in the reactors ranged from 17.9:1 to 63.6:1. Positive, significant linear effects (p<0.05) on biogas production were observed for the two factors evaluated. The maximum biogas production observed was 521.5 mL per gram of initial COD when the co-digestion was conducted with 4 g L-1 of crude glycerol and 5 g L-1 of swine manure after 35 days. The highest biogas yield was obtained with a C/N ratio of 29.4 and pH close to 6.5.