Abstract: Scale is removed, and its formation is reduced or prevented in the effluent section of a sewage treatment plant, by adding a solution containing a small amount of phosphonate and a terpolymer of acrylic acid. The treatment is especially effective in anaerobic areas of the plant, which includes transfer lines from sludge handling systems, pumps, piping, valves, overflow lines, and possibly centrifuges, etc., and particularly where the Ca+ 2 exceeds about 600 ppm, and the system alkalinity varies from about pH 6-9.