中文摘要：

The effects of hydraulic retention time （HRT） on the nitrification activities and population dynamics of a conventional activated sludge system fed with synthetic inorganic wastewater were investigated over a period of 260 days. When the HRT was gradually decreased from 30 to 5 h, the specific ammonium-oxidizing rates （SAOR） varied between 0.32 and 0.45kg NH4＋-N （kg mixed liquor suspended solids （MLSS）·d）-1, and the specific nitrate-forming rates （SNFR） increased from 0.11 to 0.50kg NO3-N （kg MLSS·d）1l, showing that the decrease in HRT led to a significant increase in the nitrite oxidation activity. According to fluorescence in situ hybridization （FISH） analysis results, the proportion of ammonia-oxidizing bacteria （AOBs） among the total bacteria decreased from 33% to 15% with the decrease in HRT, whereas the fraction of nitrite-oxidizing bacteria （NOBs）, particularly the fast-growing Nitrobacter sp., increased significantly （from 4% to 15% for NOBs and from 1.5% to 10.6% for Nitrobacter sp.） with the decrease in HRT, which was in accordance with the changes in SNFR. A short HRT favored the relative growth of NOBs, particularly the fast-growing Nitrobacter sp., in the conventional activated sludge system.