An apparatus, method and system is provided for treating sewage sludge by heating the same in a container to drive off pathogens and/or pasteurize the sewage sludge while the material is tumbled in the container and with moisture gases being evaporated therefrom and drawn off from the container. After treatment the treated sludge is discharged from the container. There is provided at least one weight-responsive member on which the container is mounted, and a control is provided connected to the one or more weight-responsive member whereby the solids content of the treated material can be determined by measuring the difference in weight of material in the container, before and after moisture is drawn off from the material and prior to its discharge from the drum. The control is preferably effected by means of a computer.