An inlet assembly for a burner comprising a combustion chamber, said inlet assembly comprising: an inlet nozzle defining an inlet aperture coupleable with an inlet conduit adapted to provide an effluent gas stream for treatment by said burner, a non-circular outlet aperture, a nozzle bore extending along a longitudinal axis between said inlet aperture and said outlet aperture for conveying said effluent gas stream from said inlet aperture to said outlet aperture for delivery to said combustion chamber of said burner, said nozzle bore having an inlet portion extending from said inlet aperture and an outlet portion extending to said non-circular outlet aperture, a baffle coupling said inlet portion with said outlet portion, said baffle defining a baffle aperture (270, 270A, 270B) positioned within said nozzle bore, said baffle aperture having a reduced cross-sectional area compared to that of said outlet portion adjacent said baffle, wherein said baffle aperture is configured to generate a vortex in said effluent gas stream within said outlet portion and a secondary gas stream nozzle is positioned to inject a secondary gas stream to flow tangentially to said vortex and said secondary gas stream nozzle coupleable with a secondary gas stream conduit providing said secondary gas stream, said secondary gas stream nozzle being positioned to mix said secondary gas stream with said effluent gas stream within said nozzle bore wherein said vortex has an inner flow region proximate said baffle aperture and an outer flow region proximate said outlet portion nozzle bore and said secondary gas stream nozzle is positioned to inject said secondary gas stream to flow tangentially with a direction of flow of said vortex in said inner flow region. an inlet aperture coupleable with an inlet conduit adapted to provide an effluent gas stream for treatment by said burner, a non-circular outlet aperture, a nozzle bore extending along a longitudinal axis between said inlet aperture and said outlet aperture for conveying said effluent gas stream from said inlet aperture to said outlet aperture for delivery to said combustion chamber of said burner, said nozzle bore having an inlet portion extending from said inlet aperture and an outlet portion extending to said non-circular outlet aperture, a baffle coupling said inlet portion with said outlet portion, said baffle defining a baffle aperture (270, 270A, 270B) positioned within said nozzle bore, said baffle aperture having a reduced cross-sectional area compared to that of said outlet portion adjacent said baffle, wherein said baffle aperture is configured to generate a vortex in said effluent gas stream within said outlet portion and a secondary gas stream nozzle is positioned to inject a secondary gas stream to flow tangentially to said vortex and said secondary gas stream nozzle coupleable with a secondary gas stream conduit providing said secondary gas stream, said secondary gas stream nozzle being positioned to mix said secondary gas stream with said effluent gas stream within said nozzle bore wherein said vortex has an inner flow region proximate said baffle aperture and an outer flow region proximate said outlet portion nozzle bore and said secondary gas stream nozzle is positioned to inject said secondary gas stream to flow tangentially with a direction of flow of said vortex in said inner flow region.