Nitrification options for pig wastewater treatment

Nitrification is a necessary and often limiting process in animal waste treatment for removal of nitrogen as N2 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 × 20m 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-m3 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.