Continued growth in digester projects
By EPA AgStar
By EPA AgStar
in digester projects
There are now 125 livestock manure anaerobic digester
systems in operation in the U.S., according to the Environmental
May 4, 2009 – There are now 125 livestock manure anaerobic digester systems in operation in the U.S., according to the Environmental Protection Agency.
In 113 of the operational systems, the captured biogas is used to generate electrical power, with many of the farms recovering waste heat for the electricity-generating equipment for on-farm use. These systems generate about 244,000 megawatt-hours (MWh) of electricity per year. The remaining 12 systems use the gas in boilers, upgrade the gas for injection into a natural gas pipeline, or simply flare the captured gas for odor control. Most digester systems (78 percent) operate at dairy farms and are largely concentrated in the Midwest, West, and Northeast.
The majority of commercially operating digesters (78 percent) are plug flow and complete mix systems operating at mesophilic temperatures (95ºF – 105ºF). The next most popular system is covered lagoons, operating at ambient temperature. More specific details about the systems are posted in AgSTAR’s Anaerobic Digester Database.
Although the majority of systems are still farm-owned and operated with only livestock manure as the feedstock, other approaches are emerging. These include the codigestion of high strength organic wastes (e.g., food processing wastes) to increase gas production per unit volume of reactor; third-party owned/operated systems; centralized systems handling manure from multiple farms; and direct gas sales to customers or gas utilities.