In　order　to　meet　increasingly　stringent　discharge　standards,　new　applications　and　control　strategies　for　the　sustainable　removal　of　nitrogen　from　wastewater　have　to　be　implemented.　In　the　past　years,　numerous　studies　have　been　carried　out　dealing　with　the　application　of　fuzzy　logic　to　improve　the　control　of　the　activated　sludge　process.　In　this　paper,　fuzzy　control　strategies　of　predenitrification　systems　are　presented　that　could　lead　to　better　effluent　quality　and,　in　parallel,　to　a　reduction　of　chemicals　consumption.　Extensive　experimental　investigations　on　lab　scale　plant　studies　have　shown　that　there　was　excellent　correlation　between　nitrate　concentration　and　ORP　value　at　the　end　of　the　anoxic　zone.　Results　indicated　that　ORP　could　be　used　as　an　on-line　fuzzy　control　parameter　of　nitrate　recirculation　and　external　carbon　addition.　The　optimal　value　of　ORP　to　control　nitrate　recirculation　and　external　carbon　addition　was　-　86　+/-　2　mV　and　-　90　+/-　2　mV,　respectively.　The　results　obtained　with　real　wastewater　also　showed　the　good　performance　and　stability　of　the　fuzzy　controllers　independently　from　external　disturbances.　The　integrated　control　structure　of　nitrate　recirculation　and　external　carbon　addition　in　the　predenitrification　system　is　also　presented.