Biological nitrogen and phosphorus removal are being recommended at several wastewater treatment facilities in the U.S. to control eutrophication in water bodies receiving their effluent. In several instances, nitrogen removal is being recommended on a year round basis at plants located in the temperate climates. Concerns have been raised regarding the cost of additional reactors and clarifiers required for nitrogen removal in winter using activated sludge systems. Several facilities do not have the space to construct additional units. This research was undertaken to evaluate the potential for reducing reactor and clarifier requirements, maximize use of existing facilities, and economize costs for year round nitrification and nitrogen removal. The purpose was to develop Integrated Fixed Film Activated Sludge Systems in which biofilm support media was installed in the activated sludge basins to enhance nitrogen removal. The objectives were to evaluate the COD removal, nitrification and denitrification kinetics, which would help develop design and mathematical models for the process, and optimize the layout in terms of costs and media required for nitrogen removal. A bench scale pilot study was undertaken in conjunction with two full scale studies with two types of media: (i) free floating media and (ii) media fixed in frames. Amongst biofilm support media in the first category, sponge cuboids (Captor) were selected. For the second category, rope type Ringlace media was selected. Following preliminary screening for satisfactorily simulation of full scale conditions in a bench scale system, the IFAS-Sponge system was selected for kinetic coefficient evaluation and IF AS system model development. / Ph. D.