Upflow anaerobic sludge blanket digestion
Upflow anaerobic sludge blanket (UASB) technology, normally referred to as UASB reactor, is a form of anaerobic digester that is used for wastewater treatment. The UASB reactor is a methanogenic (methane-producing) digester that evolved from the anaerobic clarigester.
Source: Wikipedia — Upflow anaerobic sludge blanket digestion (CC BY-SA 4.0)