Nitrification is a necessary and often limiting process in animal waste treatment for removal of nitrogen as N-2 through biological nitrification/denitrification systems. We evaluated three technologies for enhancing nitrification of pig lagoon wastewater prior to denitrification: overland flow, trickling filter, and a bioreactor using nitrifying pellets. The overland flow system consisted of a 4 x 20-m plot with 2% slope with a subsurface impermeable barrier receiving a total N loading rate of 64-99 kg N ha(-1) day(-1). Total N removal efficiency ranged from 36 to 42%, and 7% of the total N application was recovered in the effluent as nitrate. The trickling filter consisted of a 1-m(3) tank filled with marl gravel media which supported a nitrifying biofilm. Lagoon wastewater was applied as a fine spray on the surface at hydraulic loading rates of 684 litres m(-3) day(-1) and total N loading rates of 249 g m(-3) day(-1). The media filter treatment transformed up to 57% of the inflow total N into nitrate when wastewater was supplemented with lime. The nitrifying pellets technology used acclimated nitrifying cells immobilised in 3-5 mm polymer pellets. Pig wastewater was treated in an aerated fluidised reactor unit with a 15% (w/v) pellet concentration. Nitrification efficiencies of more than 90% were obtained in continuous flow treatment using total N loading rates of 438 g N m(-3) day(-1) and hydraulic residence time of 12 h. Two conclusions are suggested from this research: (1) that substantial nitrification of pig lagoon wastewater can be attained particularly using aerobic treatments with enriched nitrifying populations, and (2) that large mass removal of N from pig wastewater may be possible by sequencing nitrification and denitrification unit processes.