A heated digester performs the same biological function as a lagoon in a much shorter time because of the higher temperature. This concentration can be achieved by underfloor scrapers or managed pull plug manure collection. A conservatively designed heated mixed digester is sized for a 20 day retention time. Lagoons vs. Digesters - Costs Per unit of volume, a heated concrete digester will cost more than a lagoon. However, a heated digester requires a much smaller volume than a lagoon.
Costs vary between regions, soil types and digester types.
Substitution of a digester investment for lagoon investment yields excess methane which is essentially a free energy source. Additional savings are realized by reduction of lagoon surface area and land application costs. Also, the stored effluent is of uniform quality and will not be an odor source when land applied. AgSTAR AgSTAR is a voluntary program that promotes recovery and use of methane from animal manure. AgSTAR is one of many voluntary initiatives under the US Climate Change Action Plan to Reduce Greenhouse Gases.