Example of the use of additives and separating the solids from the liquids using a filter bed separator with containers and stirrers for treatment with (1) slurry pumped into the separator, (2) coagulants added to the slurry pumped into the first container, and (3) polymers added to slurry transferred from the first to the second container. The additives may be added into the tubes transferring the slurry to the separator and between containers, or the additives may be added to the slurry in the containers that are equipped with a stirrer: vigorous stirring may break up the flocs.