An air stripper apparatus comprising: a cabinet having a fluid inlet port for admitting a contaminant-entrained fluid, a clean fluid discharge port adjacent a lower area of the cabinet, a clean air inlet port, and a contaminant-entrained air discharge port adjacent an upper end of the cabinet; a plurality of trays removably supported within the cabinet in a horizontal orientation; a plurality of tray support members for supporting the trays removably within the cabinet; a plurality of floor sections disposed fixedly within the cabinet and respectively adjacent the plurality of trays; a central vertical wall which divides the cabinet into two vertically arranged sections; each of the trays having a plurality of perforations for allowing air to be blown in an upward direction through each tray and through the contaminant-entrained fluid collecting on each tray, wherein the air flowing through the contaminant-entrained fluid residing on each tray removes and entrains contaminants therein from the contaminant-entrained fluid; a plurality of downcomers disposed within the cabinet and respectively adjacent the plurality of floor sections for helping to control a flow of the contaminant-entrained fluid through the cabinet; and a plurality of weirs located respectively adjacent the plurality of downcomers and operable to help the contaminant-entrained fluid collect on the trays, wherein each of the downcomers is pivotally movable in a first direction away from the associated weir in response to a rising level of the contaminant-entrained fluid on the associated floor section, and in a second direction into contact with the associated weir to block air flow between the associated weir and the downcomer. a cabinet having a fluid inlet port for admitting a contaminant-entrained fluid, a clean fluid discharge port adjacent a lower area of the cabinet, a clean air inlet port, and a contaminant-entrained air discharge port adjacent an upper end of the cabinet; a plurality of trays removably supported within the cabinet in a horizontal orientation; a plurality of tray support members for supporting the trays removably within the cabinet; a plurality of floor sections disposed fixedly within the cabinet and respectively adjacent the plurality of trays; a central vertical wall which divides the cabinet into two vertically arranged sections; each of the trays having a plurality of perforations for allowing air to be blown in an upward direction through each tray and through the contaminant-entrained fluid collecting on each tray, wherein the air flowing through the contaminant-entrained fluid residing on each tray removes and entrains contaminants therein from the contaminant-entrained fluid; a plurality of downcomers disposed within the cabinet and respectively adjacent the plurality of floor sections for helping to control a flow of the contaminant-entrained fluid through the cabinet; and a plurality of weirs located respectively adjacent the plurality of downcomers and operable to help the contaminant-entrained fluid collect on the trays, wherein each of the downcomers is pivotally movable in a first direction away from the associated weir in response to a rising level of the contaminant-entrained fluid on the associated floor section, and in a second direction into contact with the associated weir to block air flow between the associated weir and the downcomer.