Abstract: A single treatment compartment has a liquid metal inlet and outlet and a connection to a liquid metal-input trough. A treatment gas is injected into the liquid metal arranged in at least one sidewall of a ladles. The liquid metal inlet and outlet have an orifice positioned so as to be entirely underneath a level of the liquid metal during the treatment, in order to prevent entry of ambient air into the compartment during treatment. The treatment compartment includes an upstream part and a downstream part. The gas injection is accomplished in the upstream part. The compartment further has a filter located in the downstream part for degassing and filtering the liquid metal. Injection and filtration occur in close proximity to one another and within the same single treatment compartment.