The CAPTOR process had been proposed as a method of quickly and economically uprating existing activated sludge processes. A full-scale evaluation was initiated for uprating the activated sludge plant and Freehold Water Reclamation Works (near Stourbridge, England) to achieve year-round nitrification. The process suffered from several major operational problems. The report describes how these problems were tackled by pilot-scale work and in a demonstration plant at Freehold before implementation on the full-scale plant at Freehold. The work showed that it was possible to raise the biomass concentration in the CAPTOR unit to 6000 - 8000 mg/l, but it also showed that the respiration rate of the biomass in the pads is less than the same biomass if freely suspended and less than normal activated sludge. Several variants of the CAPTOR process were tried out in the pilot and full-scale systems. An economic evaluation of the CAPTOR variants was carried out.