A novel moving bed contactor has been used in filtration studies of municipal waste at various stages within a trickling filter plant. Granular, buoyant filter medium is slurried with process feed and introduced to the bottom of a column equipped with lateral retaining screens and filter medium harvesting machinery, both positioned toward the top of the column. Within the column, filter medium rises by buoyancy and forms a porous plug that traps suspended solids from the feed stream. Filtered liquid is removed from the lateral screen, and soiled filter medium is continuously removed from the column top, washed and recycled to the column bottom. The process operates stably and dependably on all feeds tested--raw wastewater, primary clarifier effluent, and trickling filter effluent. Filtration of alum-coagulated feed is less effective than that of untreated feed. Costs of the process, including equipment, power, construction, and amortization, were estimated.