Abstract: The present invention provides methods for increasing soluble chemical oxygen demand (sCOD) in sewage sludge. These methods include passing the sewage sludge through one or more devices that contains (a) a hollow body provided with a straight-through passage of substantially constant cross-section, the passage having an inlet end and an outlet end for the entry and discharge respectively of the sewage sludge, (b) a transport fluid nozzle substantially circumscribing and opening into the passage intermediate the inlet and outlet ends thereof, (c) a transport fluid inlet communicating with the transport fluid nozzle for the introduction of a transport fluid, and (d) a mixing chamber being formed within the passage downstream of the transport fluid nozzle. The sewage sludge is then passed through a digester.