Enhancement of biogas production from cattle manure using glycerine phase as a co-substrate in anaerobic digestion

This study investigated the effect of glycerine phase on the anaerobic digestion of cattle manure under mesophilic conditions. The process was carried out in semi-continuous stirred tank reactors at a constant organic loading rate of 2.3 g VS/L.d and a hydraulic retention time of 30 days. It was found that the addition of 10% (as volatile solids) glycerine phase to cattle manure produced 3.1-times more biogas than cattle manure alone (237.5 L vs. 76.4 L) and a 10% higher methane content (69% vs. 59%). Biogas formation during co-digestion was strongly correlated with the concentrations of ammonium nitrogen (r = 0.89, p < 0.05) and volatile fatty acids (r = -0.71, p < 0.05), which resulted in a decrease in biogas production over time despite a stable pH value. The proposed use of glycerine phase could provide an advanced anaerobic digestion system that is technologically simple, has a positive energy balance, and produces upgraded biogas, although additional monitoring of the concentration of volatile acids and ammonium nitrogen is needed to maintain stable biogas production. These findings will be useful for reducing demand for non-renewable energy resources, and more broadly, they will assist in the shift from a traditional economy to a circular bioeconomy.