Keeping the Neighbors Happy - Reducing Odor while Making Biogas

Controlled anaerobic digestion with biogas recovery is one method to stabilize manure, reduce odor, and produce an energy resource that offers a return on investment. Substituting a digester for the treatment portion of a lagoon results in a very low cost supply of methane for use on the farm. The installation cost of treatment volume at an Iowa sow farm collecting manure at 3% total solids is approximately $21/sow in a 12' deep unlined lagoon, or $35/sow in a concrete, heated, mixed digester. The lagoon produces no benefit as propane replacement while the digester would produce $9/sow/yr. Cost and benefit comparisons for nursery and- finishing -farms are included with supporting assumptions. The calculated conclusions are supported by previously built digester systems. Digesters at Rocky Knoll Farms of Lancaster, PA (I 982 - 800 sows farrow-to- finish) and Valley Pork in 7 Valleys, Pennsylvania (1986 - 1,500 sows, farrow-to-finish) stabilized manure, collected usable biogas and satisfied the odor objections of the neighbors, town council and state regulators. The systems had simple cash paybacks in less than 5 years. In the last 2 years, at least a dozen farms have installed anaerobic digesters. Seven farms were assisted by the EPA, USDA, and DOE sponsored AgSTAR program. AgSTAR provided technical assistance through out the development, installation, start-up and operating phases of these anaerobic digestion projects. Three dairy plug flow digesters (NY, CT, OR), three covered pig manure lagoons (NC, VA, IA) and one heated mixed pig manure digester (EL) have been placed in operation since January 1997 with AGSTAR technical assistance. The farms and their digester systems are described. The cost and benefits of the digester systems are summarized.