Abstract: An odor control system for a settling tank containing a pool of wastewater to be clarified in which suspended particles are removed by gravitational settling and the water at the surface of the pool is clarified. Supported within the tank is an elongated effluent trough having a weir at one side thereof which extends upwardly therefrom to permit clarified water from the pool to spill over into the trough. Mounted over the trough along its full length is a hood having a side wall which extends into the pool at a position displaced from the weir the hood being constituted by a series of sections. The hood acts to capture noxious gases emitted into a region above the surface of the water therebelow as the clarified water spills over into the trough.