Patent ID: 9187355
Filing Date: 2015-11-17
Classification: C02F,C12M,Y02E,Y02W

Abstract:
1. A method of removing excess water from raw sludge to produce concentrated sludge particles and a volatile fatty acid rich liquor stream comprising the steps of: (i) introducing the raw sludge with an initial solids concentration of between 1% and 5% weight/volume (w/v) and from 65 to 85% weight/weight organic matter into a fermentation vessel; (ii) fermenting the sludge under essentially anaerobic conditions at a temperature in the range of 30° C. to 42° C. using only indigenous bacteria present in the sludge to generate nascent biogas bubbles comprising greater than 80% carbon dioxide said fermenting being substantially completed in a period of between 12 hours and 120 hours under a substantially hydraulically quiescent condition leaving the sludge undisturbed to allow said bubbles to effect flotation of sludge particles present in the fermenting sludge to form a concentrated surface layer of said particles and in which said particles in said concentrated surface layer are digested and sink to the bottom of the vessel to form a layer of digested sludge thereby achieving a phase separation of the sludge during this period into three layers comprising: (iii) separately removing the solid phase layer and liquid phase layer; and (iv) deriving a volatile fatty acid liquor stream from the liquid phase layer.