There are four general categories of Anaerobic Digester designs:
- Covered anaerobic lagoon digester: Sealed with flexible cover, with methane recovered and piped to the combustion device. Some systems use a single cell for combined digestion and storage.
- Plug flow digester: Long, narrow concrete tank with a rigid or flexible cover. The tank is built partially or fully below grade to limit the demand for supplemental heat. Plug flow digesters are used at dairy operations that collect manure by scraping.
- Complete mix digester: Enclosed, heated tank with a mechanical, hydraulic, or gas mixing system. Complete mix digesters work best when there is some dilution of the excreted manure with water (e.g., milking center wastewater).
- Dry Digestion: Upright, silo-style digesters made of concrete and steel with rigid cover. Dry digesters operate at 20 to 42 percent total solids, which allow them to combine high dry matter manure and crop residuals with very dilute liquid manures or co-substrates.