Fine Bubble diffused aeration (FBDA) contract and Ancillary Works

The total flow to the Castletroy Wastewater Treatment Works in 2013 was 2,586,025m3 with the average daily flow to the plant during 2013 at 7,085 m3/day. Basing the calculation on an average BOD of 230 mg/l for the influent waste stream, this equates to a P.E. of 27,159 P.E.

The upgraded aeration tanks No.1 and No.2 shall be suitable for treatment of wastewater for a population equivalent of 35,000 PE (2,100 kg/day BOD).

Plant operational details are as follows:

Design Parameters Original Design Parameters Current (2013 Report by LCC to EPA) Required in Upgrade
Population Equivalent (PE) 29,477 27,178 35,000
BOD loading kg/day 1,769 1,631 2,100


Aeration Tank Dimensions/Volume

Castletroy WWTP Aeration Tank Details Based on Current Operational Level Max @ Inlet Pipe Invert Level
No. of Cells 2 2 No.
TWL 10.25 10.4 mOD
Floor of Ditch 5.25 5.25 mOD
Total Depth 5 5.15 M
Free Board 1.2 1.2 M
Length 32.5 32.5 m
Width 16.25 26.25 m
Height to TWL 5 5.15 m
Volume per tank 2640.63 2719.84 m3
Total Volume
(Tank1 & Tank 2 combined)
5281.25 5439.69 m3


The overall scope of this project was to replace the existing vertical surface aerators with a Fine Bubble Diffused Aeration System to cater for a design population of 35,000 PE

The scope included the following main elements of work:

  • Removal of existing aeration equipment.
  • Fully functional fine bubble diffused aeration (FBDA) system on stainless steel removable grids
  • Stainless steel piping
  • Design, manufacture and installation of 4 no. bridges to provide access for all valves on FBDA System
  • Five no. blowers Aerzen Hybrid D24S positive displacement blowers
  • Complete mechanical and electrical installation
  • Adjustments to existing electrical system and PLC/SCADA to cater for new FBDA system
  • Testing and commissioning

In addition to the FBDA contract, Conway Engineering also completed the following ancillary works:

  1. Removal of existing stairs and handrailing on both aeration tanks to replace with triple height to 1200mm hand railing and new stairs so as to adhere to H&S regulations
  2. Supply and M&E installation of 2 no. step screens. Manufacture and installation of horizontal screw conveyor to complete screening system at inlet works
  3. Refurbishment of Jones Atwood 900 series grit removal system to put back into operation
  4. Refurbishment of Salsnes Filter to put back into operation including M&E installation of corresponding pump and air blower