A crankcase ventilation system for separating oil particles from crankcase blow-by gases of an internal combustion engine, ICE, comprising a housing; a disc stack separator arranged within the housing comprising a chamber; a rotor comprising an oil separating element arranged within the chamber and spaced from one or more walls of the chamber; and a shaft configured to rotatably mount the oil separating element; a first gas inlet for supplying the crankcase blow-by gases to the oil separating element along the shaft; and a first gas outlet for discharging the at least partially oil-separated gases; characterized in that the system further comprises a filter element comprising a second gas inlet, a second gas outlet, and a filter arranged between the second gas inlet and the second gas outlet, wherein the filter is composed of a layer of arranged fibers; and wherein the first gas inlet is configured to be connected to a crankcase blow-by outlet of the ICE, wherein the first gas outlet is connected to the second gas inlet, and wherein the filter element is not connected to the shaft. a housing; a disc stack separator arranged within the housing comprising a chamber; a rotor comprising an oil separating element arranged within the chamber and spaced from one or more walls of the chamber; and a shaft configured to rotatably mount the oil separating element; a first gas inlet for supplying the crankcase blow-by gases to the oil separating element along the shaft; and a first gas outlet for discharging the at least partially oil-separated gases; characterized in that the system further comprises a filter element comprising a second gas inlet, a second gas outlet, and a filter arranged between the second gas inlet and the second gas outlet, wherein the filter is composed of a layer of arranged fibers; and wherein the first gas inlet is configured to be connected to a crankcase blow-by outlet of the ICE, wherein the first gas outlet is connected to the second gas inlet, a chamber; a rotor comprising an oil separating element arranged within the chamber and spaced from one or more walls of the chamber; and a shaft configured to rotatably mount the oil separating element; an oil separating element arranged within the chamber and spaced from one or more walls of the chamber; and a shaft configured to rotatably mount the oil separating element; a first gas inlet for supplying the crankcase blow-by gases to the oil separating element along the shaft; and a first gas outlet for discharging the at least partially oil-separated gases; characterized in that the system further comprises a filter element comprising a second gas inlet, a second gas outlet, and a filter arranged between the second gas inlet and the second gas outlet, wherein the filter is composed of a layer of arranged fibers; and wherein the first gas inlet is configured to be connected to a crankcase blow-by outlet of the ICE, wherein the first gas outlet is connected to the second gas inlet, a filter element comprising a second gas inlet, a second gas outlet, and a filter arranged between the second gas inlet and the second gas outlet, wherein the filter is composed of a layer of arranged fibers; and wherein the first gas inlet is configured to be connected to a crankcase blow-by outlet of the ICE, wherein the first gas outlet is connected to the second gas inlet,