Abstract: A method of biological treatment of effluent and the like in a packing tower or bed. Individual plastic packing elements are disposed in open-weave or open-mesh sacks, and are arranged in the tower or bed. Effluent is then passed through the tower or bed, bacteria and the like forming as a biological film on wetted surfaces of the packing elements. The open-weave arrangement allows the passage of air to the biological film, and allows passage of the biological film out of the tower when it becomes loosened from time to time. The sacks are disposed permanently in the tower, no cleaning or the like thereof being necessary.