A filter-adsorption media, such as activated carbon, is supplied to one end of a screw conveyor having a variable pitch along its length with the greater pitch being at the supply end. Sewage, such as from a marine toilet, is passed through a macerator and chemically treated before being introduced into the central portion of the screw conveyor to be mixed with the filteradsorption media and compacted as the screw conveyor is rotated. The compacting produces a mixture of filter-adsorption media and sludge at the discharge end while the liquid is passed through the conveyor in counter-flow relationship, to the incoming filter-adsorption media and through the filter-adsorption media, and then to a discharge.