The　aim　of　this　work　is　to　study　the　effects　of　six　operational　variables,　i.e.,　dissolved　oxygen　(DO),　nitrate　recirculation　flow,　sludge　recycle　flow,　sludge　wastage　flow,　external　carbon　dosage,　and　anoxic　volume　fraction,　on　the　performance　of　nitrogen　removal　and　its　control　in　a　pre-denitrification　plant.　The　results　obtained　show　that　the　six　operational　variables　have　a　significant　influence　on　nitrogen　removal　in　such　a　system,　while　the　utilization　of　the　control　strategies　can　improve　the　situation　to　a　significant　extent.　The　control　of　DO　concentration　should　be　correlated　with　the　influent　ammonia　load,　the　effluent　requirement　and　nitrification　type.　The　anoxic　effluent　nitrate　concentration　should　be　controlled　at　ca.　2　mg/L　or　the　ORP　value　at　the　end　of　the　anoxic　zone　should　be　controlled　at　ca.　-90　mV.　The　control　of　the　sludge　recycling　flow　by　online　monitoring　of　the　sludge　blanket　height　(SBH),　is　an　alternative　to　the　conventional　control　of　the　constant　sludge　recycle　flow.　It　may　be　possible　to　achieve　the　automatic　control　of　sludge　wastage　flow　by　online　measuring　of　the　ammonia　concentration　and　the　nitrification　capacity　of　the　sludge.　The　recirculation　of　nitrate　and　external　carbon　dosage　should　be　simultaneously　controlled　to　optimize　nitrogen　removal.　The　anoxic　volume　fraction　should　also　be　optimized,　to　ensure　a　good　balance　between　nitrification　and　denitrification.