Abstract
Three airlift reactors with sponge-carriers were operated by a stepwise increase of ammonium loading rate at different temperatures, 25, 30, 35°C, to investigate effects of temperature and ammonium concentration on partial nitrification to nitrite. A high ammonium loading rate (1kg NH4+-N·m-3.·day-1) caused nitrite accumulation accompanied with remaining ammonium. The ratio of nitrite accumulation to ammonium oxidation strongly correlated with free ammonia more than ammonium concentration or temperature. The free ammonia concentration of 8mg NH3·L-1 allowed the almost occurrence of partial nitrification having the ratio of 0.8. The result suggests free ammonia must be a crucial factor to control partial nitrification. Cloningresults of sludge samples showed Nitrospira genus of nitrite-oxidizing bacteria was a predominant microorganism under the complete nitrification condition, while ammonia-oxidizing bacteria predominated under the partial nitrification condition.
