Above-ground continuously stirred tank reactor (CSTR)

A continuously stirred tank reactor is a medium-rate anaerobic tank, usually steel, mixed so the bacteria stay in contact with the feed. Working volumes in the reference designs run from about 200 m³ to about 10,000 m³.

Use it where an in-ground reactor will not fit, and on fibrous or oily feeds: shredded crop residues, fat, oil and grease, dairy, brewery, and similar industrial streams. Retention is longer than in a high-rate tank, which is why the process is more tolerant and why the footprint is still smaller than a lagoon. Primary settling is often unnecessary because the raw solids are digested in the tank.

See also in-ground digesters and biogas.