Aerators: Aerators are devices used in sewage treatment plant to mix the atmospheric air with the sewage in proper ratio to induce bacterial processes. In diffuser type aerator, the liquid flow generated by an impeller causes negative pressure to form on the impeller vanes and draw in air from atmosphere. The aspirated air mixed with water viciously by mechanical forces inside the impeller and guide van transform into tiny bubbles. Moreover, the mixed flow of air and water is evenly discharged in multiple directions along the circumference. The compounded action of the air lift and convective currents that are generated in the process makes aeration and agitation very efficient and increases the amount of oxygen dissolved in the water. Jet type Aerator is a submersible pump combined with a venturi and jet based diffuser. The primary purpose is to transfer oxygen to the liquid or sludge. Jet aerators are easily configured into any basin geometry including circular, rectangular , looped reactors and sloped wall basins. In this aerator the aspirated air mixes with water and is ejected through the diffuser simultaneously agitating and aerating the ponded water. The mixed air water is ejected powerfully in one direction which effectively agitates the water across a wide area.