A targeted study on possible free ammonia inhibition of Nitrospira

Batch tests were carried out with Nitrospira in mixed and pure cultures using concentrations of free ammonia widely believed to be inhibitory to nitrite-oxidizing organisms. The mixed culture batch tests were conducted with mixed liquor from a bench scale completely stirred tank reactor (CSTR) treating a synthetic wastewater having a low C:N ratio. Nitrospira were confirmed as the dominant nitrite oxidizers via RNA slot blotting. Nitrospira moscoviensis were used for the pure culture trials. The results from this study suggest that free ammonia (NH 3 -N) concentrations of up to 10 mg/L were not inhibitory to Nitrospira either in situ or in pure culture. Key words: fatty acid methyl esters, free ammonia inhibition, molecular methods, nitrification, nitrite, Nitrobacter, Nitrospira, nitrous acid, nitrous oxide, RNA slot blotting, wastewater treatment.