A solid bowl screw centrifuge includes a housing and a rotor rotatably mounted in the housing. The centrifuge has a rotatable drum having an axis of rotation, the drum having a cylindrical section having a length L1 and a conical section having a length L2. The centrifuge also has a first inlet for feeding a suspension to be processed into the drum and a liquid outlet arranged in the cylindrical section of the drum and a solids outlet arranged in the conical section of the drum. A screw is arranged in the drum and rotatable at a differential speed relative to the rotatable drum, the drum and the screw together forming the rotor. The centrifuge also a second inlet for supplying an additive to a solid phase within the drum.