The treatment of landfill leachate obtained from municipal solid waste (MSW) by using a lab-scale sequencing batch reactor(SBR) was studied.The aim of achieving and stabilizing partial nitrification and denitrification and the characteristics of advanced nitrogen removal were investigated.The experimental results showed that for 95 days running

stable partial nitrification with nitrite accumulation rate above 92.5% was achieved and maintained successfully.The stable biological nitrogen removal via partial nitrification and denitrification was realized and the average removal efficiency of NH+4 -N and TN were above 97.2% and 91.7%

respectively.The DO

ORP and pH could be used as the process control parameters for SBR reactor

because the characteristic points on the profiles indicated exactly the nitrification and denitrification end point.The nitrite oxidizing bacteria (NOB) was more sensitive than ammonia oxidizing bacteria (AOB) to the free ammonia (FA) and free nitrite acid (FNA)

so the activity of NOB was inhibited by the synergetic effect of highly concentrated FA and FNA in the SBR nitrification.Furthermore

the key factor of achieving and stabilizing partial nitrification and denitrification for a long time was optimization of nitrifying microbial population by the assistance of process control

which was proved by FISH analysis.