Anaerobic digestion process for sewage sludge
OwnerYoshio Kobayashiinventor
Life of this patent
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Abstract
An anaerobic digestion process for sewage sludge comprises a first step of dewatering the raw sewage sludge to provide a solids content therein of at least 10 weight %. A portion of digested sludge resulting from methane fermentation is recirculated and added to the dewatered raw sludge, the weight ratio of digested sludge to dewatered raw sludge being at least 1:1. The resulting mixture is homogeneously kneaded and then subjected to methane fermentation. At least one of the dewatered raw sludge prior to the recirculating step and the kneaded sludge mixture during methane fermentation is subjected to thermal treatment at a temperature not less than 50.degree. C.
Claims8
An anaerobic digestion process for sewage sludge, comprising an acid formation step causing acid formation fermentation and a methanation step, said process comprising the steps of:
- dewatering raw sewage sludge to provide a solids content therein of at least 10 weight %;
- recirculating a portion of digested sludge resulting from acid formation fermentation;
- adding said dewatered raw sludge to said recirculated portion of digested sludge resulting from acid formation fermentation, the weight ratio of digested sludge to dewatered raw sludge being at least 1:1;
- homogeneously kneading the resulting mixture;
- subjecting the kneaded sludge mixture to acid formation fermentation;
- and
- subjecting products of the acid formation fermentation to methanation fermentation to generate methane;
- at least one of (a) said dewatered raw sludge prior to addition to said recirculated portion of digested sludge and (b) said kneaded sludge mixture in said acid formation fermentation step being subjected to thermal treatment at a temperature not less than about 50.degree. C.
Dependencies are inferred from the claim text.