The sludge remaining at the treatment plant is pumped into large tanks called anaerobic digesters, where microorganisms break down the organic matter into methane gas and a more stable sludge.
Jääkmuda pumbatakse suurtesse mahutitesse, mida kutsutakse anaeroobseteks metaankääritustankideks, kus mikroorganismid lagundavad orgaanilise aine metaangaasiks ja stabiilsemaks setteks.