Landfill leachate is treated by two-stage UASB-A/O process.Batch tests were conducted with the activated sludge taken from A/O reactor

which is of good properties of biological nitrogen removal. The impacts of salinity shocks on SOUR

ammonia oxidation rate

and nitrite accumulation rate of different microorganisms

as well as profile of pH

are investigated

especially

its effect on N2O production during nitrite denitrification.The results show that the order of inhibition strength by salinity is follows:NOB>AOB>carbon oxidation bacteria;while the reaction for salinity shocks:carbon-oxidizing bacteria and NOB are better than AOB.For all microorganisms tested

the ammonia oxidation rate decrease gradually with increase of salinity

but the reduction level is quite different.At the same concentration of initial ammonia

nitrite accumulation rate goes slightly up with the increase of salinity

from 93.1% at 5 g稬-1 salt to 98.6% at 35 g稬-1 salt.The curve of pH can be used as on-line control parameters

indicating the end of short-nitrification and short-denitrification by salinity shock.The delay of nitrite denitrification and the increase of N2O peak concentration would appear during the process of salinity shock.