Fine Bubble diffused aeration (FBDA) contract and ancillary works

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.[separator style_type=”single” top_margin=”10″ bottom_margin=”20″ sep_color=”#eaeaea” border_size=”” icon=”” icon_circle=”” icon_circle_color=”” width=”” alignment=”center” class=”” id=””]
Aeration Tank Details
No. of Aeration Tank: 2
Top of Tank Wall (mOD): 46.5
Operational TWL (mOD): 45.25
Tank Floor Level (mOD): 41.35
Tank Depth (meters): 3.9
Cell Length (meters): 19.5
Cell Width (meters): 19.5
Volume m3 per tank: 1483

The scope of the FBDA project included the following main elements of work:

  • Removal of existing surface aerators in each of the two tanks
  • Fully functional fine bubble diffused aeration (FBDA) system on stainless steel removable grids
  • Stainless steel piping
  • Three Aerzen D24S Hybrid positive displacement air blowers were installed (Duty Tank No.1/Duty Tank No.2 with 1xNo. common standby)
  • Two no. VSDs for existing RAS pumps
  • Mechanical and electrical installation
  • Adjustments to existing electrical system to cater for new FBDA system
  • Installation of power metering
  • Testing and commissioning

The aeration system installed utilised the Aquaconsult AEROSTRIP diffusers mounted on liftout grids with an intelligent control system to alternately switch on and off as required.
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Ancillary Works
In addition to the FBDA contract, Conway Engineering also completed the following ancillary works:

  1. Refurbishment of step screen to put back into operation, mechanical and electrical installation of same.
  2. Removal of existing stairs and handrailing to replace with triple height to 1200mm hand railing and new stairs so as to adhere to H&S regulations.