(621c) Biogas Production Using Glycerol, the Biodiesel by-Product, as the Carbon Source

With the increasing popularity of biodiesel, there has been an increase in production of crude glycerol as a by-product. This increase has flooded the market and has driven the price of glycerol down. Over the past 3 year(s), the price of glycerol has fallen from $0.95/lb in 2003 to $0.49/lb in 2005. New uses of glycerol need to be identified. An option being investigated at Mississippi State University is the anaerobic digestion of glycerol to produce biogas. By using mesophilic microorganisms to consume the glycerol by-product, gases such as carbon dioxide and methane can be produced. Instead of flaring the biogas, as is typically done in a wastewater treatment plant, the biogas could serve as a source of recovered energy. This energy could then be used to provide heating and electrical power for biodiesel plants. This project has examined the effect of four different added nutrient concentrations. Preliminary results indicate that samples with a lower concentration of added nutrients produce methane at a greater rate (1/10 and ½ of the recommended nutrients produced at rates of 0.000125 and 0.000168 moles of CH4 per day) than those with samples with greater concentrations of nutrients (2X the concentration of the recommended nutrients produced at a rate of 0.0000486 moles of CH4 per day). This indicates that the methanagens responsible for consuming the glycerol may prefer oligotrophic conditions. This project also provides a comparison between pure glycerol and crude glycerol as a carbon substrate source for the microorganisms. Changes in pH and chemical oxygen demand (COD) were monitored throughout the duration of the project.