In　this　paper,　an　adaptive　interval　type-2　fuzzy-neural　sliding　mode　control　(AT2FSC)　method　using　a　disturbance　observer　is　developed　for　wastewater　treatment　process　(WWTP)　with　unknown　external　disturbance.　Firstly,　to　overcome　the　modeling　complexity　of　WWTP,　a　simplified　interval　type-2　fuzzy　neural　network　(IT2FNN)　is　used　to　approximate　the　uncertainty　dynamics　of　WWTP.　Then,　the　network　update　parameters　are　reduced　while　ensuring　the　modeling　accuracy.　Secondly,　the　nonlinear　disturbance　observer　is　designed　in　AT2FSC　to　estimate　the　unknown　external　disturbance.　Then,　the　robustness　of　AT2FSC　under　the　influence　of　external　disturbances　can　be　guaranteed.　Thirdly,　the　adaptive　sliding　mode　gain　is　designed　to　achieve　stable　control　of　WWTP.　The　Lyapunov　theory　has　finally　demonstrated　that　the　proposed　AT2FSC　approach　can　guarantee　system　stability.　The　outcomes　of　the　simulation　demonstrate　the　ability　of　the　proposed　AT2FSC　approach　to　provide　efficient　control　performance　and　suppress　external　disturbances　in　WWTP.　©　2022　IEEE.