In an effort to convert waste streams to energy in a green process, glycerol from biodiesel manufacturing
has been used to increase the gas production and methane content of biogas within a mesophilic anaerobic
co-digestion process using primary sewage sludge. Glycerol was systematically added to the primary
digester from 0% to 60% of the organic loading rate (OLR). The optimum glycerol loading range was from
25% to 60% OLR. This resulted in an 82–280% improvement in specific gas production. Following the feeding
schedule described, the digesters remained balanced and healthy until inhibition was achieved at 70%
glycerol OLR. This suggests that high glycerol loadings are possible if slow additions are upheld in order to
allow the bacterial community to adjust properly. Waste water treatment plant operators with anaerobic
digesters can use the data to increase loadings and boost biogas production to enhance energy conversion.
This process provides a safe, environmentally friendly method to convert a typical waste stream
to an energy stream of biogas.