Birr WwTP was constructed in 1989 and has a design P.E. of 12,000. The plant consists of inlet works with archimedean screw pumps, inlet screening and degritting facilities, two aeration tanks each with a working capacity of 1,483 m3, two clarifiers and two picket fence thickeners. Aeration in each aeration tank was provided by 1 xNo. 30kW vertical surface rotor driven by 30 kW Danfoss variable speed drives which were controlled by the dissolved oxygen setpoint in each tank.