In this method the surface of sewage is agitated violently with the help of some mechanical equipment to encourage absorption of oxygen from atmosphere. There are two well known forms of mechanical aerator. Vertical surface aerator and Horizontal surface aerator
They consist of electrically driven propellers (vanes) mounted in either a floating or fixed supports. They throw the bulk liquid (sewage) through air and oxygen transfer occurs both at the surface of the droplets and at the surface of the bulk liquid and is then mixed by the currents produced by agitation. In this method the performance is seriously affected by ice formation in winter.