The　phenomenon　of　sludge　bulking,　which　can　be　classified　as　slight　or　serious　abnormal　operating　conditions　according　to　sludge　volume　index　(SVI),　is　a　widespread　problem　in　wastewater　treatment　process.　In　this　paper,　a　piecewise　sliding-mode　control　(PSMC)　strategy　is　developed　to　overcome　the　adverse　effects　and　furthermore　improve　the　operating　performance　for　wastewater　treatment　process　under　different　operating　conditions　of　sludge　bulking.　First,　a　soft　sensing　model　of　SVI　based　on　fuzzy　neural　network　is　established.　Then,　it　can　online　determine　the　state　of　sludge　and　whether　sludge　bulking　has　occurred.　Second,　in　view　of　the　specific　operating　condition　of　sludge,　a　piecewise　sliding-mode　controller　is　designed.　Then,　the　sludge　bulking　can　be　eliminated　by　regulating　the　concentration　of　dissolved　oxygen　and　nitrate　nitrogen.　Third,　the　boundary　condition　of　PSMC　is　evaluated.　Then,　the　stability　of　the　control　system　is　proved　on　the　basis　of　ensuring　the　boundary　condition　of　PSMC.　Finally,　the　performance　of　PSMC　is　verified　in　the　benchmark　simulation　platform.　The　results　further　demonstrate　the　effectiveness　of　the　proposed　control　method.　IEEE