Abstract: Apparatus for purifying a gas stream such as air laden with particulate matter and containing unwanted contaminant gases. A bladed rotor supporting a perforated tube therein is positioned near the bottom of a water column and is revolved at critically high speed, such as over 600 revolutions per minute while a gas-stream inlet communicates with the interior of the rotor via the perforated tube. At the critical rotational speed water from the water column is prevented from entering between the blades of the rotor, the rotation of which draws contaminant inlet gas thereto through the perforated tube. The gas stream drawn into the rotor through the perforated tube is thereafter expelled by centrifugal force from the blades of the rotor into the water column thus affording cleaning of the gas stream by the water in the column. Water from the column is preferably withdrawn and prepared for reuse, as by filtering, neutralizing, pumping and, if necessary, cooling.