An effluent processing apparatus is provided for a vehicle air brake charging system. The effluent processing apparatus has an inlet port through which effluent from a purge valve of an air dryer can be received and an outlet port. The effluent processing apparatus further has a quadric surface defining an effluent flow chamber that is connected in fluid communication between the inlet port and the outlet port. The quadric surface is provided for extracting contaminants from an effluent stream as the effluent stream flows from the inlet port along the quadric surface to the outlet port.